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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 677-681 
    ISSN: 1572-8854
    Keywords: Anthraquinone ; crystal structure ; intramolecular hindrance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the monoclinic space group, P21/c;a=12.938(1),b=11.041(1),c=19.285(2) Å, β=104.314(8)°,Z=4. Refinement based on 1660 unique observed reflections converged toR=0.054. The anthraquinone moiety is distorted due to intramolecular steric hindrance from the tosylate groups.
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  • 2
    ISSN: 1572-8854
    Keywords: Organoiron complex ; dinuclear complex ; crystal structure ; phosphonium ylid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the centrosymmetric monoclinic space group P21/n withZ=4. The cation consists of two (η5-C5h5)Fe(CO) units which are linked via a metal-metal bond (Fe(1)−Fe(2)=2.530(1) Å), a bridging carbonyl ligand (Fe(1)−C(4)=1.912(8) Å. Fe(2)−C(4)=1.940(9) Å) and a bridging phosphonium ylid ligand (Fe(1)−C(1)=1.991(6) Å, Fe(2)−C(1)=1.985(6) Å and C(1)−P(1)=1.781(6) Å).
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 747-752 
    ISSN: 1572-8854
    Keywords: Phosphine oxide ; quaternary ammonium ; water-soluble phosphine ; crystal structure ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the centrosymmetric triclinic space group $$P\bar 1$$ withZ=4. The crystallographic asymmetric unit contains two independent cations; interatomic distances within these include P=O=1.47(1) and 1.47(1) Å, P−C6H5=1.78(2)–1.81(1)Å and P−CH2CH2NMe3 +=1.80(1) and 1.81(1) Å. The phosphine oxide moiety is involved in intermolecular hydrogen bonding ()...H−C, with O...H≥2.42Å) and the iodide is involved in I...H−C contacts with I...H≥3.10Å.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 185-189 
    ISSN: 1572-8854
    Keywords: Solid-solid reaction ; inclusion compound ; p-toluidine ; cholic acid ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Cholic acid undergoes solid-solid reactions with some aromatic molecules to form inclusion compounds. Simple shaking of a mixture of powdered cholic acid andp-toluidine results in formation of the 1∶1 (host:guest) inclusion compound which has the same structure as that formed by conventional crystallization methods: monoclinic space groupP21 witha=13.577(4),b=8.078(2),c=14.182(6) Å, β=114.42(3)°,Z=2 andR 1=0.061 for 2680 unique reflections.
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  • 5
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; disordered structure ; crystal structure ; solvate ; triphenylphosphine ; bipyridyl
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru{4,4′-(t-Bu)2bpy}2(PPh3)Cl+][ClO 4 − ·0.5(toluene)·0.5(MeCN), where 4,4′-(t-Bu)2bpy=4,4′-di(t-butyl)-2,2′-bipyridyl crystallizes with an ordered racemic mixture of the chiral cations in the centrosymmetric triclinic space group $$P\bar 1$$ (No. 2). The structure was refined toR=4.42% for those 6426 reflections with 20=5–50o and |F o|〉6σ(F). Ruthenium ligand distances are Ru−Cl=2.423(2)Å, Ru−PPh3=2.346(2)Å and Ru−N=2.056(4)–2.098(4)Å. Both the Ru(II)-containing cation and the perchlorate anion are ordered, but the toluene and acetonitrile exhibit an interesting type of scrambled disorder about the inversion center atx=1,y=1/2,z=0.
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  • 6
    ISSN: 1572-8862
    Keywords: Rhenium ; dirhenium complexes ; rhenium-rhenium multiple bonds ; isocyanide ligands ; carbonyl ligand ; structural isomers ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The monocarbonyl complex Re2Cl4(µ-dppm)2(CO) reacts with xylyl isocyanide in acetonitrile to afford the bioctahedral complex (CO)Cl2Re(µ-dppm)2 ReCl2(CNxyl), 2b. This is a different structural isomer from the edge-sharing bioctahedral complex Cl2Re(µ-Cl)(µ-dppm)2ReCl(CNxyl) or this same stoichiometry which A formed when acetone is be reaction solvent. The complex2b reacts with a further equivalent of xylNC in the presence of TlO3SCF3 in dichloromethane to form a red complex of composition [Re2Cl3(µ-dppm)2 (CO)(CNxyl)2]O3SCF3. 3, which has the open bioctahedral structure [(xylNC)2ClRe(µ-dppm)2ReCl2(CO)]O3SCF3. This is a third isomeric form of this dirhenium cation: the previously isolated green and yellow forms have edge-sharing bioctahedral structures. Crystal data for3 at 295 K: orthorhombic space group Pbca (No. 61) witha=22.654(5) Å,b=22.717(4) Å,c=27.324(4) A,V= 14061(7) Å3, andZ = 8. The structure was refined to R = 0.059 (R, = 0.134 ) for 14164 data. The Re-Re distance is 2.3833(8) Å.
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  • 7
    ISSN: 1572-8854
    Keywords: Ruthenium(II) ; bipyridyl ; phenyldi(o-tolyl)phosphine ; solvate ; hydrogen bonding ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru(bpy)2{PPh(o-tolyl)2}Cl+][ClO4 −] crystallized from a solution in dichloromethane as the dichloromethane-water solvate. The structure was refined toR=4.5% for those 2433 reflections with |F o|〉6σ(|F o|). The octahedral Ru(II) cation is associated with metal-ligand distances as follows: Ru−Cl=2.434(3)Å, Ru-PPh(o-tol)2=2.382(2)Å, and Ru−N=2.037(7)–2.088(7)Å. The structure is stabilized by a hydrogen-bonded CH2Cl2...ClO4 −...H2O channel which incorporates adventitious water of crystallization.
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  • 8
    ISSN: 1572-8854
    Keywords: Silver ; stearate ; triphenylphosphine ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal and molecular structure of [bis-triphenylphosphine-silver(I) stearate], [((C6H5)3P)2Ag(O2C(CH2)16CH3)], has been determined by single crystal X-ray analysis: the space group is PT witha=12.021(4),b=13.916(5)1,c=14.678(5) Å, α=95.952(5), β=101.249(6), γ=93.259(5)°,V=2388(2) Å3, andD calc=1.293 g/cm3 forZ=2. The silver is four coordinate: the carboxylate symmetrically chelates the silver while the triphenylphosphine ligands occupy the third and fourth coordination sites. The strong bonding nature of the phosphine ligands, as indicated by the Ag−P bond lengths, 2.446(3) and 2.424(3) Å, dominates the coordination sphere of the silver and forces the initial carboxylate ligand to rearrange from bridging to chelating resulting in weaker Ag−O bonds, as indicated by the extended Ag−O bond lengths, 2.399(8) and 2.449(8) Å. Unlike the free acid, the long hydrocarbon chain is not linear, and exhibits disorder in the lattice. The structure of the title complex explains the dramatic shift in solubility properties compared to the starting phosphine free silver carboxylate.
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  • 9
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; organoruthenium compound ; bis(1,2-diphenylphosphino)ethane ligand ; ruthenium-nitro complex ; crystal structure ; cyclopentadienyl derivative ; methanol solvate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title complex crystallizes in the centrosymmetric monoclinic space group C2/c (No. 15) withZ=8. The structure was refined toR=4.49% for those 2745 independent reflections with 2θ=5–50o and |F σ|〉6σ(F). Ruthenium-ligand distances are as follows: Ru-P=2.284(2) and 2.286(2) Å, Ru-NO2=2.049(6) Å and Ru-C(Cp)=2.210(10)-2.246(9) Å. Bond lengths within the nitro ligand are N(1)-O(1)=1.226(10) Å and N(1)-O(2)=1.244(10) Å. The methanol of solvation is ordered but is subject to large thermal vibrational motions.
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  • 10
    Electronic Resource
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    Journal of chemical crystallography 26 (1996), S. 461-465 
    ISSN: 1572-8854
    Keywords: Molecular dynamics ; crystal structure ; TOT clathrate ; thiophene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Tri-o-thymotide (TOT) forms a cage-type clathrate with the thiophene guest molecule in a host:guest ratio of 2∶1. This clathrate crystallizes in the trigonal system (space groupP3121). The unit cell, of dimensionsa=b=13.585(4),c=29.914(12)Å, contains 6 TOT and one thiophene molecule. The crystal structure, established by direct methods (R=0.053), indicates that the host cavity has an oblate-ellipsoid shape with a crystallographic twofold axis parallel to the largest dimension of the cage. The guest molecule within the cavity is disordered. Molecular dynamics simulations have been performed and indicate that the guest molecules have hindered molecular freedom around the shortest ellipsoid axis of the cavity, and may produce a dynamic disorder in the cage of the TOT clathrate.
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  • 11
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; tri-n-propylphosphine ; terpyridine ; ruthenium-nitro complex ; crystal structure ; disordered ligands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexmer,trans-[Ru(NO2)(trpy)(PPr3) 2 + ][ClO 4 − ]crystallizes in the centrosymmetric orthorhombic space group Pnma withZ=4. Both the ruthenium(II) cation and the perchlorate ligand lie about crystallographic mirror planes. The nitro ligand is not coplanar with the Ru(trpy) moiety and suffers from two fold disorder about its Ru−N bond such that the two sets of oxygen atoms have symmetry-related sites above or below the crystallographic mirror plane. The n-propyl groups within the PPr3 ligands suffer from disorder of their C(α) and C(β) atoms but share common C(γ) sites. Ruthenium-ligand distances are: Ru−PPr3=2.398(2)Å, Ru−NO2=2.053(7) Å, Ru−N(trpy, outer)=2.078(6) and 2.092(6) Å and Ru−N(trpy, central) =1.965(6) Å.
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  • 12
    ISSN: 1572-8854
    Keywords: Chromium ; carbonyl ; arene ; acetal ; crystal structure ; conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The structures of the (benzene dialkylacetal)tricarbonyl chromium complexes [η6-C6H5-CH(OR)2]Cr(CO)6 (R=Me,1; Et,2), are reported. The compounds were examined as part of a study of the conformations of the tripodal tricarbonylchromium group. For [η6-C6H5-CH(OMe)2]Cr(CO)3,1, monoclinic,P21/c (# 14),a=15.235(1) Å,b=6.5304(5) Å,c=12.702 Å, β=103.197(1)o,Z=4. For [η6-C6H5-CH(OEt)2]Cr(CO)3,2, monoclinic,P21/c (# 14),a=9.859(3) Å,b=10.547(3) Å,c=15.138(3) Å, β=108.42(2)o,Z=4. The data show that the molecules adopt the expected “three-legged piano stool” structure. The carbonyl ligands in1 adopt an eclipsed arrangement with respect to the arene ring and its substituent, while those in2 are staggered. These conformations are consistent with the notion that the acetal substituent behaves largely as an electroneutral group, or at most as a weak electronic acceptor.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 26 (1996), S. 389-392 
    ISSN: 1572-8854
    Keywords: p-Methoxyphenyltelluro ; x-ray diffraction ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract C23H18TeO,M r=437.97, $$P\bar 1$$ ,a=9.940(2),b=13.664(3),c=7.895(2) Å, α=80.60(1), β=69.71(2), γ=75.95(1)°,V=972.0(4) Å3,Z=2,R=0.041 for 2668 observed reflections. The Te−C bond distances are 2.109(5)Å and the C−Te−C angle is 96.0(2)°. The phenyl rings are planar to within experimental accuracy, making dihedral angles of 64.6(2), 65.3(2) and 31.1(3)°.
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  • 14
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    Journal of chemical crystallography 26 (1996), S. 403-406 
    ISSN: 1572-8854
    Keywords: Cyclotrithiazene ; arylaminophospine ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound (C6H5)2(OC4H8N)P=N−S3N3 crystallizes in the space group $$P\bar 1$$ with unit cell parametersa=9.3900(2),b=9.4747(1),c=11.3850(3) Å, α=95.73(4), β=96.85(6), γ=104.26(2)o, and Z=2. The tricoordinated sulfur of the cyclotrithiazene ring deviates from the mean plane of other skeletal atoms by 0.683(4) Å. The angle at this atom is the smallest in the ring and is enclosed by the longest S−N bonds observed in the ring.
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  • 15
    ISSN: 1572-8854
    Keywords: Copper(II) complex ; crystal structure ; coordination polymer ; betaine ; dicarboxylate ligand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Three polymeric copper(II) complexes of a flexible double betaine, namely, [{Cu(L)Cl2(H2O)} n ]·2 n H2O (1), [{Cu(L)Br2(H2O)} n ]·2nH2O (2), and [{Cu(L)(H2O)4} n ](ClO4)2n ·2nH2O (3) [L=−O2CCH(Me3N+)CH2CH2CH(Me3N+CO2], have been prepared and characterized by singlecrystal X-ray analysis. Isomorphous complexes (1) and (2) crystallize in space groupC2/c (No. 15) witha=17.725(3),b=5.958(2),c=19.077(3) Å, β=110.70(1)o,V=1881.4(4) Å3, Z=4 anda=18.268(4),b=5.948(3),c=19.166(5) Å, β=109.08(2)o,V=1964.7(9) Å3, Z=4, respectively. Complex (3) belongs to space groupPĪ (No. 2) witha=6.203(1),b=9.293(2),c=12.035(2) Å, α=86.56(2), β=87.33(3), γ=71.23(2)o,V=655.4(2) Å3 and Z=1. The crystal structure of (1) and (2) features an infinite zigzag chain composed of an alternate arrangement of metal atoms and double betaines ligands, with each Cu(II) atom in a distorted CuX2O3 [X-Cl, Br] square-pyramidal geometry, and hydrogen bonding between adjacent chains leads to a layer structure concentrated the (200) family of planes. Complex (3) exhibits a layer structure corresponding to the (001) family of planes, in which neighboring chains constructed from the metal atoms and the double betaine ligands are cross-linked by hydrogen bonding between the aqua ligands. The Cu(II) atom is coordinated in a CuO6 octahedral geometry with Jahn-Teller distortion.
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  • 16
    Electronic Resource
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    Journal of chemical crystallography 26 (1996), S. 503-508 
    ISSN: 1572-8854
    Keywords: Tin(IV) sodium(I) complex ; ethylenediaminetetraacetic acid ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract NaSn(OH)(edta)(H2O) is monoclinic, space groupP21/c, witha=9.747(3)Å,b=9.121(3)Å,c=16.430(6)Å, β=98.69(4)°, Å3, andZ=4. The coordination environment of Sn(IV) is a capped octahedron. Sn−O distances range from 1.990(6)Å to 2.351(7)Å. Na(I) is five coordinated to three different edta molecules. Na−O distances range from 2.283(9)Å to 2.414(7)Å. The edta ligand presents the E, G/R conformation. The crystal structure is composed of sheets parallel to (001): inside a sheet Sn(OH)(edta) molecules are connected to each other by the Na(I) interactions.
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  • 17
    Electronic Resource
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    Journal of chemical crystallography 26 (1996), S. 515-518 
    ISSN: 1572-8854
    Keywords: Antiarrhythmic agent ; crystal structure ; absolute configuration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the orthorhombic space groupP212121, withZ=4,a=4.770(1)Å,b=6.620(1)Å,c=37.550(7)Å,R=0.04. The most important factors affecting conformation of the molecules are: the protonation state of the N(9) atom andortho-substitution of the benzene ring in the acetanilide system. Protonation promotes an extended form of the molecule and 2,6-substitution forces a twist of at least 60° between the benzene ring and amide group planes. The resulting separation of lipophilic (xylidine) and amine groups, being two important pharmacophores, equals about 5Å in tocainide and all other structures comprising the amino-2,6-dimethylacetanilide system.
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  • 18
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    Journal of chemical crystallography 26 (1996), S. 553-557 
    ISSN: 1572-8854
    Keywords: Silver(I) complex ; synthesis ; crystal structure ; spectroscopic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The reaction of [Ph3PAgI]4 with sodium phenylacetate in MeOH and CH2Cl2 at room temperature gave rise to a binuclear silver complex with triphenylphosphine and phenylacetate mixed ligands, [Ph3PAg(O2CCH2Ph)]2. The crystal and molecular structure of the complex has been determined by single crystal X-ray diffraction analysis. The space group is $$P\bar 1$$ witha=9.198(2),b=9.516(2),c=13.842(3) Å, α=102.00(3), β=108.34(3), γ=93.58(3)°,Z=1, andDc=1.506 g cm−3. The silver atoms are each coordinated by one phosphorus atom from triphenylphosphine and two oxygen atoms from the carboxylate groups in a T-shape. The complex is further characterized by its IR,1H, and31P NMR spectra.
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  • 19
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; tri-n-propylphosphine ; bipyridyl ; crystal structure ; disorder
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru(bpy)2(PPr3)Cl+][ClO 4 − ] · 0.5 (toluene) crystallizes as a racemate in the monoclinic space group P21/n. Both the PPr3 ligand and the toluene of crystallization are subject to disorder. Ruthenium—ligand distances are: Ru−PPr3=2.348(2) Å, Ru−Cl=2.426(2) Å and Ru−N(bpy)=2.035(6)–2.112(5) Å.
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  • 20
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; terpyridine ; triphenylphosphine ; ruthenium-nitro complex ; crystal structure ; pseudo-lattice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexmer,trans-[Ru(NO2)(trpy)(PPh3) 2 + ][PF 6 − ] crystallizes in the centrosymmetric monoclinic space groupP21/n withZ=4; the ruthenium atom lies close toy=1/4 and all data withh+l=2n+1 are systematically weak. The trpy ligand is not strictly planar, but has a “dish-like” geometry. The nitro ligand is rotated from the plane of the Ru(trpy) moiety, the N3Ru/NO2 interplanar angle being 32.5o. Ruthenium-ligand distances are: Ru−PPh3=2.418(4) Å and 2.429(4) Å, Ru−NO2=2.063(12) Å, Ru−N(trpy, outer)=2.100(12) Å and 2.116(12) Å and Ru−N(trpy, central)=2.004(11) Å.
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  • 21
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    Journal of chemical crystallography 26 (1996), S. 661-665 
    ISSN: 1572-8854
    Keywords: N,N′-bis(2-hydroxyphenyl)butanediamide ; crystal structure ; hydrolysis product
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The structure of N,N′-bis(2-hydroxyphenyl)butanediamide has been determined. The molecule consists of two 2-hydroxyphenyl moieties which are attached (at the 2 position) to the two nitrogens of the butanediamide. The compound C16H16N2O4 crystallizes in the monoclinic space group P21/c witha=5.576(1),b=4.8853(6),c=25.397(6) Å and β=90.58(1)°.
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  • 22
    ISSN: 1572-8854
    Keywords: Organotin ; crystal structure ; flavone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The 1∶1 adduct of chlorotriphenyltin with 2′,6′-dimethoxyflavone, (C35H29O4ClSn)Mr=667.78, crystallizes in the triclinic space groupP1 with the following data:a-9.094(2),b=12.369(3),c=14.674(3) Å, α=74.78(2), β=77.00(2), γ=73.06(3)°,V=1503.8(4) Å3,Z=2, Mo-Kα, μ=9, 8 cm−1,Dc=1.475 g cm−3, F(000)=676,T=293K. The structure was solved by direct-methods and has been refined to a finalR value (l〉3σ(I)) of 0.0301. The flavone coordinates to the tin atom through the carbonyl oxygen atom. The metal center exhibits a trigonal bipyramidal configuration with the three phenyl groups in equatorial positions.
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  • 23
    ISSN: 1572-8854
    Keywords: Betaine ; 4-dimethylaminopyridinioacetate ; hydrogen bonding ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystalline dihydrate and hydrochloride trihydrate of a new betaine, namely, L·2H2O (1) and [L2H]Cl·3H2O(2) (L=p-Me2NC5H4N+CH2CO2), have been synthesized and characterized by X-ray crystallography. Molecule L in compound1 [space groupPbcn, witha=15.732(3),b=7.894(2),c=18.304(4) Å, andZ=8] possesses approximateC s symmetry. The formation of hydrogen bonds by water molecules bridging neighboring carboxy oxygen atoms leads to an infinite two-dimensional network composed of a packing of two different kinds of 12-membered rings. In compound2 [space group PT witha=7.341(2),b=9.543(2),c=17.010(4) Å, α=82.43(2)°, δ=80.34(2)°, λ=74.05(2)°, andZ=2], the carboxylate groups of a pair of betaine molecules are bridged by a proton to form a dimeric cation L2H+ with a very strong asymmetric hydrogen bond of length 2.464(7) Å. The crystal structure features a hydrogen-bonded corrugated ribbon comprising an alternate arrangement of edge-sharing centrosymmetric (H2O)4(Cl−)2 and (H2O)4 rings running parallel to thea axis.
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  • 24
    ISSN: 1572-8854
    Keywords: Bidentate ligand ; crystal structure ; pyrazolyl group ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound lies on a site of C2 symmetry, with the two planar pyrazolyl moieties oriented at 86.1° to one another. The hydrogen atoms were located and refined.
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  • 25
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    Journal of chemical crystallography 26 (1996), S. 219-222 
    ISSN: 1572-8854
    Keywords: Steroid ; organometallic ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 3α-Triphenylstannylcholest-5-ene (1) has been synthesised and its molecular structure has been determined by single crystal X-ray diffraction. Refinement in the triclinic space groupP1 witha=7.805(6),b=7.862(5),c=32.351(10)Å, α=90.87(8), β=94.77(8) and γ=101.15(4)o converged atR=0.063. One of the two crystallographically independent molecules in the unit cell has a patially disordered side chain. The bond lengths and valency angles about tin indicate some steric hindrance due to the proximity of one of the phenyl rings with the B ring of the steroid nucleus.
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  • 26
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    Journal of chemical crystallography 26 (1996), S. 841-846 
    ISSN: 1572-8854
    Keywords: Cu(II) resorcylidene aminoguanidine ; synthesis ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The tridentate Schiff base, β-resorcylidene aminoguanidine (RAG)1 was synthesized from 2,4-dihydroxybenzaldehyde and aminoguanidine and complexed with copper(II) to form a copper(II)-β-resorcylidene aminoguanidine (Cu-RAG)2 complex. X-ray diffraction analysis of compound2 (orthorhombic, Pnma,a=11.674(1);b=6.7198(7);c=17.836(2) Å) revealed a square-planar copper(II) cation with a tridentate·ligand bound through two nitrogen atoms (N1 and N3) of the aminoguanidine moiety and an oxygen (O1) of the monodeprotonated dihydroxybenzaldehyde function. The remaining coordination site was occupied by chloride and the structure was rigidly planar as demanded by the restrictions of the crystallographic space group. The unit cell contents exhibited an extended sheet-like structure constructed via hydrogen bonds both intermolecularly and involving two water molecules (O3 and O4) also restricted by the same mirror symmetry. The remaining water (O5) provided for interlayer hydrogen bonding.
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  • 27
    ISSN: 1572-8854
    Keywords: Pyrazolyl group ; crystal structure ; bidentate ligand ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound consists of two planar pyrazolyl fragments oriented at 73.0° to each other and linked to a common carbon atom. All hydrogen atoms were located unambiguously and their positions were refined.
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  • 28
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; bipyridyl ; diphenyl(o-tolyl)phosphine ; dichloromethane solvate ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru(bpy)2 {PPh2(o-tol)}Cl][ClO4] crystallizes from dichloromethane as the sesqui-dichloromethane solvate. The complex crystallizes in the monoclinic space group P21/n with Z=4. The structure was refined toR=5.50% for those 2552 independent reflections with |F 0|〉6σ(|F 0|) The octahedral Ru(II) cation is associated with the following bond lengths: Ru-PPh2(o-tol)=2.360(3)Å. Ru−Cl=2.433(2)Å and Ru−N(bpy)=2.041(8)–2.095(8)Å. Both the perchlorate anion and the dichloromethane molecules of solvation exhibit large amplitudes of vibration. One dichloromethane molecule lies in a general position, the other lies about an inversion center and suffers from disorder.
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  • 29
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    Journal of chemical crystallography 26 (1996), S. 615-619 
    ISSN: 1572-8854
    Keywords: Disordered trifluoromethyl group ; quinoline ; crystal structure ; AM1 calculation ; mefloquine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallized in space groupPna21 with lattice constantsa=13.406(1),b=18.799 (4), andc=4.785(1). The molecule is essentially flat with only fluorine atoms, methylene hydrogen atoms, and the hydroxyl hydrogen atom out of the plane of the quinoline ring. Only one of the trifluoromethyl groups of the title compound is disordered following a pattern observed in other crystal structures. Quantum chemical calculations at the AM1 level are consistent with this phenomenon. Although the carbon atom of the fixed trifluoromethyl group is further from the quinoline nitrogen atom than the carbon atom of the disordered trifluoromethyl group, the fluorine atoms of the fixed trifluoromethyl group more closely approach the quinoline nitrogen atom by 0.3 Å if the C(8)−C(10) bond in the crystal structure is freely rotated.
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  • 30
    ISSN: 1572-8862
    Keywords: Niobium(III) ; edge-sharing bioctahedra ; di-p-tolylformamidinato ; thiomethoxide ; double-bond ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The reaction of NaEt3BH with Nb2(μ-SMe2)3Cl6 results in the transfer of a hydride ion to dimethylthioether with concomitant production of methane. Further reaction with potassium di-p-tolylformamidinate, KDTolF, yields Nb2(μ-SMe)2(μ-DTolF)2η2-DTolF:)2.2 toluene, 1. In the latter, two thiomethoxide ions and two DTolF groups bridge the trivalent niobium atoms. Each of the other two DTolF groups chelate a metal atom to give the molecule an edge-sharing bioctahedral structure, The niobium-niobium distance of 2.655(2) A is consistent with the presence of a double bond between the metal atoms.
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  • 31
    ISSN: 1432-0649
    Keywords: 42.80 ; 81.60 ; 42.55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The kinetics of cavitation and associated photo-mechanical effects induced by underwater pulsed-laser irradiation of solid targets has been studied experimentally and analyzed with theoretical methods. A xenon-chloride excimer laser of 150 ns pulse duration has been utilized to produce ablation and local photofragmentation of artificial samples of hard tissues at fluences of 12–24 J/cm2. The evolution of pressure wave and cavitation formations developing in the liquid from the target surface after laser irradiation has been observed with a time-resolved imaging technique employing a pump-probe laser arrangement. The analysis of experimental results has been performed by using the theoretical model of “point explosion” that has been successfully applied to fit the cavitation kinetics, providing also quantitative information on the energy transfer during photo-acoustic interactions.
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  • 32
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    Applied physics 62 (1996), S. 235-240 
    ISSN: 1432-0649
    Keywords: 42.80 ; 78.65 ; 81.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Laser-induced transformations (optical and compositional) of amorphousMO x thin films are studied as a function of the oxygen content and the nature of theM element,M being either a semiconductor (Ge) or a semi-metal (Sb). A high optical contrast in reflectivity is always found associated to the first laser pulses, this process being unaffected by the presence of oxygen. Next pulses lead to a process which may involve optical changes depending on the environmental conditions. Whereas the former optical changes are most likely related to a structural process which is completed before oxidation starts, the latter ones occur when irradiating at high oxygen pressures (1.2 bar) and thus they are easily related to an oxidation process. At low oxygen pressures (close to the oxygen partial pressure in air), the films show a good compositional stability upon irradiation together with a high optical contrast.
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  • 33
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    Applied physics 62 (1996), S. 77-82 
    ISSN: 1432-0630
    Keywords: 42.60 ; 81.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The direct laser writing of graduation lines in Cr thin films on glass substrates has been investigated. The Nd-YAG laser and the astigmatic optical system have been used to write rectangular holes in the Cr film. The optimal writing parameters: the laser pulse energy, the Cr layer thickness and the substrate-objective distance were determined using the optoacoustic probe beam deflection method to detect the evaporation of the material. The evaporation is concluded to be the essential process in the laser writing of graduation lines. The rims formed by the surface tension gradient at the hole edges indicate that the laser writing of graduation lines is a typical two-phase removal process.
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  • 34
    ISSN: 1432-0630
    Keywords: 68.35 ; 81.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The mechanism of KrF-excimer-laser cleaning of Si(100) surfaces was studied by Auger Electron Spectroscopy (AES) and Low-Energy Electron Diffraction (LEED) spectroscopy. The dependence of the cleaning efficiency on the laser fluence was investigated by using a mildly focused laser beam and carefully measuring the energy density distribution of the laser spot impinging on the sample. These values were compared with the AES spectra measured in different points of the irradiated area and with the morphology observed by optical microscopy. Samples as received from the manufacturer were first investigated. It was found that desorption of weakly bonded organic adsorbates occurs at energy densities as low as 0.3 J/cm2, whereas significant oxide removal takes place only at an energy density above 0.8 J/cm2, which produces damaged surface morphologies. The experimental findings, in agreement with the temperatures calculated for the laser-induced Si heating, indicated that a large fraction of the oxide film is dissolved in the molten silicon, leading to oxygen concentration below the AES detection limit only when the melted depth was of the order of several hundred nanometers. Atomically clean, damage-free Si(100) surfaces were obtained after irradiation of samples pre-etched for 1 min in a HF: H2O (5%) solution, which had only a thin SiO x (x 〈 2) layer and F, C and O containing adsorbed species. Complete contaminant elimination was achieved in this case with 15 pulses at 0.8 J/cm2 without any damaging of the surface.
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  • 35
    ISSN: 1432-0630
    Keywords: 81.40 ; 81.60 ; 82.40Z
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A thin solid C60 film has been irradiated under a fix incident angle with pulsed UV light at the wavelength of 266 nm. With scanning electron microscopy and atomic force microscopy, a surface transformation of the irradiated films has been observed to a periodic surface structure at low laser fluences in air as well as in vacuum and to strong morphology changes at higher laser fluences only in air. For both structural transformations the occuring surface chemistry has been studied with Raman spectroscopy and X-ray photoelectron spectroscopy. In the case of the periodical lines, these results in addition to a detailed discussion of the existing models for laser induced surface structures have shown that the C60 film remains a van der Waals solid but with much oxygen incorporation in the lattice and does not polymerize as it is known to happen during continuous wave irradiation. The case of strong morphology changes could be explained by detailed comparison of the obtained Raman and X-ray photoelectron spectroscopy data as the formation of a new carbon phase with diamond-like sp3 bondings through an oxygen-assisted fullerene cage opening.
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  • 36
    ISSN: 1432-0630
    Keywords: 81.40 ; 81.60 ; 72.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Multiple-shot effects in laser processing and ablation of polyimide are examined and are found to be the dominant phenomena for processes involving several hundreds or thousands of pulses. For fluences less than 260 mJ/cm2, it was found that it is impossible to cut through 75 μm polyimide foils for an arbitrarily large number of excimer pulses even though this fluence is more than ten times the single-shot ablation threshold. The halt in etching is due to the formation, over a number of shots, of a robust carbon matrix with a deep surface roughness which is also responsible for laser-induced electrical conductivity. The effect of thermal coupling between successive shots is shown to be a dominant factor in determining the electrical properties of the carbon layer. Differences in electrical conductivity of up to 12 orders of magnitude were found for only small differences in repetition rate. Transmission electron microscopy revealed the changes in microstructure responsible for the dramatic differences in electrical properties.
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  • 37
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    Applied physics 63 (1996), S. 133-138 
    ISSN: 1432-0630
    Keywords: 81.40 ; 81.60 ; 82.40 ; 82.45
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Laser-induced wet chemical etching of stainless steel 304 and Ti in phosphoric acid, sulfuric acid and aqueous KOH has been investigated using cw Ar and cw Nd : YAG lasers. Two different phases of laser-induced etching of Ti in phosphoric acid were found by electrochemical investigations. Laser-enhanced electrochemical dissolution of stainless steel was observed in the passivation and transpas sivation region. In the latter case, laser heating accelerates the metal dissolution. In the passivation region, laser heating results in a breakthrough of the passivation layer near the Flade potential. By multiple scanning microstructures of high quality and an aspect ratio 〉 10 have been produced. By EDX analysis the laser-etching process was found to be practically free of chemical residues on etched surfaces.
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  • 38
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    Applied physics 62 (1996), S. 303-311 
    ISSN: 1432-0630
    Keywords: 87.00 ; 81.60 ; 43.00
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Photomechanical fracture induced by thermoelastic stress waves is an important mechanism of tissue ablation by short laser pulses. In this study, we present experimental investigations of the fracture process in ductile, water-containing materials and compare the results with a theoretical calculation. The model describes cavitation caused by the negative part of a bipolar thermoelastic stress wave. Pulses from aQ-switched, frequency-doubled Nd:YAG laser with 8 ns duration were used to irradiate dyed water and gelatine with variable absorption coefficient. Cavitation and ablation were observed with various time-resolved methods such as stress detection, video imaging and an optical pump-probe technique for the detection of individual cavities. Quantitative agreement between experiment and simulation could be achieved in the case of cavity lifetimes, especially at low laser fluence where the bubble density is low and no coalescence takes place. An increase of the threshold energy density for ablation with rising absorption coefficient and a distortion of the thermoelastic wave in the presence of cavitation were experimentally observed and could be qualitatively explained by use of the simulation. The results obtained in this study should facilitate the choice of the optimal laser parameters for photomechanical tissue ablation.
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  • 39
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    Applied physics 63 (1996), S. 337-339 
    ISSN: 1432-0630
    Keywords: 42.60 ; 81.60
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Surface topology changes in polyimide induced by single UV-laser pulses with pulse durations between 140 ns and 5 μs are investigated by means of atomic force microscopy. With increasing fluence three different regimes are found: (a) real material removal (ablation), (b) swelling of the irradiated area above the level of the untreated surface (hump formation) and (c) lowering of the irradiated area below the level of the untreated surface (dent formation). A detailed description of these topology changes is given and different formation processes are discussed.
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  • 40
    ISSN: 1432-0630
    Keywords: 85.42 ; 81.15 ; 81.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Ultra-fine silicon quantum wires with SiO2 boundaries were successfully fabricated by combining SiGe/Si heteroepitaxy, selective chemical etching and subsequent thermal oxidation. The results are observed by scanning electron microscopy. The present method provides a very controllable way to fabricate ultra-fine silicon quantum wires, which is fully compatible with silicon microelectronic technology. As one of the key processes of controlling the lateral dimensions of silicon quantum wires, the wet oxidation of silicon wires has been investigated, self-limiting wet oxidation phenomenon in silicon wires is observed. The characteristic of the oxidation retardation of silicon wires is discussed.
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  • 41
    ISSN: 1432-0630
    Keywords: 81.60 ; 42.10 ; 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The threshold fluence,F Th, of ablation of a triazeno-polymer was measured in the low fluence range for thin films using conventional UV-spectroscopy. It was found that there is a clearly definedF Th for 308 nm irradiation between 20 and 25 mJ cm−2. In the case of 248 nm irradiation, a “threshold fluence range” between 16 and 32 MJ cm−2 was found. The ablation rate for both irradiation wavelengths depends on film-thickness. For the XeCl excimer-laser, the point at which the rate becomes independent of thickness was observed to lie at a value which did not correspond to the calculated laser penetration depth, whereas for the KrF laser the independence was not reached within the applied thickness range (up to 0.35 μm). Additional transmission measurements have been performed showing that the target transmission at 248 nm increases only slightly, whereas for 308 nm the transmission increases by a factor of approximately 4. This result shows that dynamic target absorption properties are very important for describing the ablation process. The results derived from the transmission studies and etch rates were analyzed theoretically with a two-level model of chromophore absorption. For 248 nm irradiation this model can describe the transmission behavior and the ablation rate. In the case of 308 nm irradiation, it was only possible to match one data set. A good agreement with the experimental transmission ratio does not match the ablation rate and vice versa.
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  • 42
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    Applied physics 63 (1996), S. 283-286 
    ISSN: 1432-0630
    Keywords: 81.60 ; j, 42.62 ; b, 81.60.Dq
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Laser-induced etching of polycrystalline Al2O3TiC material by tightly focused CW Ar ion laser has been investigated in both H3PO4 and KOH solutions with influence of an external electric field. It is found that a weak external electric field will change the ions distribution in chemical solutions and cause obvious change in etching behavior. The laser etching in a H3PO4 solution can be enhanced by both positive and negative biases of the substrate. While etching in a KOH solution, a positive bias can enhance the etching reaction, whereas a negative bias can suppress the etching process. It is also found that the external electric field can always enhance the mass transfer between reaction products and fresh etchant in a H3PO4 solution. It is revealed that the supply of H+ ions contributes to the etching process in a H3PO4 solution, while the supply of OH− ions contributes to the etching process in a KOH solution. The electric field can be used to control the etching process to achieve fast tuning and higher accuracy.
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  • 43
    ISSN: 1432-0630
    Keywords: 61.40 ; 61.80 ; 66.30 ; 81.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Li salts of acrylic acid were grafted to polyethylene, PE. It is known that li is mobile in this material at room temperature, and hence can act as a probe for newly introduced defects. After irradiation of PE(Li) with 100 keV He+ ions at different fluences the Li depth distributions were measured by NDP. Changes in the Li distributions are observed which are ascribed to bonding at oxygen, the latter one preferentially penetrating into the PE via the irradiation-damaged sample surface. With increasing sample age, i.e. after exposure to ambient atmosphere for more than half a year, Li appears to lose its original mobility.
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  • 44
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    Applied physics 63 (1996), S. 87-90 
    ISSN: 1432-0630
    Keywords: 42.60 ; 81.60
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Single-shot laser ablation of polyimide has been investigated with UV-Ar+-laser radiation (λ = 270-315 nm) for pulse lengths between 140 ns and 5 µs. The irradiated polymer surface was studied with respect to its morphology and ablated depth by means of atomic force microscopy. The dependence of the ablation threshold on laser pulse-length and intensity can be tentatively interpreted on the basis of a thermal process and a (thermal or non-thermal) mechanism which diminishes the activation energy for the desorption of species from the surface.
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  • 45
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    Applied physics 63 (1996), S. 179-182 
    ISSN: 1432-0630
    Keywords: 73.40 ; 73.50 ; 81.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The aim of this work was to study the charge creation in the SiO2 layer of a Si MOSFET induced by the electric field stress in the Fowler-Nordheim (FN) tunneling regime. At lower field, typical positive oxide charge generation has been observed. With an increasing stressing field, which is accompanied by an increasing FN electron injection current, negative charge creation has been found. The possible sources of charges and the mechanisms of their generation are presented.
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  • 46
    ISSN: 1090-6487
    Keywords: 74.72.Bk ; 74.72.Jt ; 64.75.+g ; 77.22.Gm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Low-temperature (120–180 K) relaxational effects are observed in oxygen-deficient RBa2Cu3O6+x (R=Y, Tm, Lu) single crystals. Isothermal holding of the crystals after rapid cooling increases their resistance. The characteristic times and the activation energy of the relaxation process, E a ≈0.46 eV, are determined. The possible relation between the observed effects and the appearance of “electronic phase separation” is discussed.
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  • 47
    ISSN: 1090-6487
    Keywords: 84.37.+q ; 74.72.Yg ; 74.72.Bk ; 74.72.Hs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The temperature dependences of the real part R s and the imaginary part X s of the surface impedance Z s =R s +iX s of the superconductor Ba0.6K0.4BiO3 (T c ≃30 K) are measured at a frequency of 9.4 GHz. Its temperature dependence Z s (T) and that of the complex conductivity σ s (T) can be described on the basis of a two-fluid model under two assumptions: The density of superconducting carriers increases linearly, and the relaxation time increases as a power law (∝1/T 5), with decreasing temperature T〈T c . This model also describes well the curves Z s (T) and σs (T) recently measured for YBa2Cu3O6.95 and Bi2Sr2CaCu2O8 single crystals.
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  • 48
    ISSN: 1090-6487
    Keywords: 74.60.+r ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The response of YBaCuO Josephson junctions on a bicrystalline substrate to the action of microwave radiation is found to contain, besides the Josephson response, a contribution associated with the tunneling of quasiparticles through channels formed by localized states in the region of the Josephson junction. It is shown that this contribution is associated with an increase in the conduction through these channels under the action of the radiation on the junction.
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  • 49
    ISSN: 1090-6487
    Keywords: 61.72.Hh ; 74.72.Bk ; 74.80.Bj ; 76.60.Lz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The nuclear magnetic relaxation of 169Tm in TmBa2Cu3O6+x (x=0.1–1.0, Δ x=0.1) and TmBa2Cu4O8 is studied at temperatures below 5 K. In all the samples, the Tm spin-lattice relaxation proceeds via intrinsic paramagnetic centers (PCs) like Cu2+ or copper-oxygen spin-polarized clusters. The experimental data for TmBa2Cu3O6+x support the idea of the structural (chemical) micro-phase separation in oxygen-deficient 123 compounds. Apparently, the samples with x⩾0.4 contain hole-poor nonsuperconducting regions, enriched with PCs, and hole-rich (PC-poor) superconducting regions. The volume fraction f n of the PC-rich phase reaches a maximum value of 0.85 at x=0.4 and decreases monotonically with increasing x (f n=0.5, 0.3, and 0.25 at x=0.5, 0.6, and 0.7, respectively). The Tm spin-lattice relaxation in the underdoped TmBa2Cu4O8 compound indicates that this sample, in contrast to oxygen-deficient TmBa2Cu3O6+x , has a homogeneous composition. However, the Tm spin-spin relaxation measurements reveal two sorts of the Tm nuclear spins in Tm124, having different NMR spectra and different relaxation times T 2. The latter result is evidence of electronic phase separation in CuO2 phases.
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  • 50
    ISSN: 1573-7357
    Keywords: 74.72.Bk ; 72.15.−v ; 76.60.−k
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The charge and spin dynamics in PrBa2Cu4O8 are investigated by means of transport and Cu NMR measurements. The magnetoresistance was found to be very small at high temperatures and increase rapidly with decreasing temperature below ∼100 K, which may be ascribed to the dimensional crossover from one to two dimensions in the charge transport in the CuO double chains. While the NMR signal from the chain Cu sites persists down to 4.2 K without any appreciable line broadening, the signal from the planar Ce sites disappears below ∼250 K indicating the long-range antiferromagnetic order of plane Cu moments. This is consistent with the view of metallic conduction along the quasi one-dimensional CuO chains.
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  • 51
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    Journal of low temperature physics 105 (1996), S. 359-364 
    ISSN: 1573-7357
    Keywords: 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The distribution of charge states of all atoms in the unit cell of RBa2Cu3Ox; x=6,7 (R = Yb, Er, Ho, Y, Gd, Eu, Sm, Nd, Pr) is determined on the basis of comparison of the theoretical calculated electric field gradient tensor and existing experimental data. The variation of the charge states of the atoms as a function of the ionic radius is analyzed.
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  • 52
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    Journal of low temperature physics 105 (1996), S. 837-842 
    ISSN: 1573-7357
    Keywords: 74.72−h ; 74.72.Bk ; 87.64.Bx ; 74.25.Kc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have performed inelastic neutron scattering and total neutron scattering experiments on the under-doped superconductor YBa2Cu3O6.6. We have found that the dynamical structure and the local structure concerned about the CuO2 plane has an anomalous temperature dependence at Tc (=57K) and well above Tc (TSG∼150K), which may be explained by a spin-gap opening.
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  • 53
    ISSN: 1573-7357
    Keywords: 74.60Jg ; 74.72.Bk ; 74.76.Bz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Epitaxial YBa2Cu3O7−δ films nucleate in c-axis oriented single-crystalline islands. The surface of the single-crystalline SrTiO3 substrates exhibit steps of one third of the YBa2Cu3O7−δ c-axis. These steps generate a mismatch in the island boundaries between the CuO2 superconducting blocks. We show that these defect regions are strong candidates for being the pinning centers responsible for the large critical currents observed in Laser Ablated and Sputtered thin films.
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  • 54
    ISSN: 1573-7357
    Keywords: 74.25.Bt ; 74.25.Fy ; 74.62.Dk ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Measurements of the anisotropic electrical resistivity, the Hall Effect, and the specific heat anomaly at Tc of Ca-doped YBa2Cu3Ox single crystals of various Ca and O contents are presented. The transport properties are discussed in terms of charge and spin separated quasiparticles and confirm that by doping Ca onto Y sites the hole concentration, nh, can be extended beyond the value achieved with O-doping alone at x=7.0. The jump in the specific heat at Tc which increases monotonously with x up to x=7.0 in Ca-free crystals displays a maximum in highly oxygenated Ca-doped crystals. This maximum, however, is displaced from the Tc(nh) maximum to higher values of nh, consistent with the model of induced superconductivity in the CuO chains.
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  • 55
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    Journal of low temperature physics 105 (1996), S. 807-812 
    ISSN: 1573-7357
    Keywords: 74.72.Bk ; 74.25.Ke ; 63.20.Kr
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    Topics: Physics
    Notes: Abstract Inelastic neutron experiments confirm the previously reported anomalous nature of the planar oxygen bond-stretching vibrations and furnish further details. It is shown that the frequency of the linear breathing mode is renormalized by 5 THz compared to insulating YBa2Cu3O6. Studies of the Cu1-apical O bond-stretching vibrations demonstrate that frequencies, line-widths and phonon intensities can well be understood within the framework of a harmonic lattice dynamical model. This rules out predictions of a double well potential and strong anharmonitity for this type of vibration.
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  • 56
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    Journal of low temperature physics 105 (1996), S. 831-836 
    ISSN: 1573-7357
    Keywords: 61.85.+p ; 74.20.Mn ; 74.25.Kc ; 74.62. Bf ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Backscattering yields in the 〈001〉 axial channeling mode using D+ ions have been measured for YBa2Cu3O7−y single crystals with Tc=59K. 68K and 91K at temperatures between 40K and 295K. In 60 K-class YBa2Cu3O7−y with significant anomalies associated with the spin gap, it is found that the channeling anomalies are observed at 130–140 K(Tpa) in addition to anomalies at Tc. The channeling anomalies at Tc follow to the shift of Tc, suggesting the phonon anomalies induced by the superconducting-gap opening. On the other hand, Tpa is found to be almost unchanged for varying Tc, although Tpa appears near the temperature where the spin gap is opened. This leads a question whether the channeling anomalies at Tpa is directly related to the phonon anomalies induced by the spin-gap opening. The existence of lattice instability is suggested as one of possible explanations for the anomalies at Tpa.
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  • 57
    ISSN: 1573-7357
    Keywords: 74.60.Ge ; 72.15.Lh ; 74.72.−h ; 72.15.Gd ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The “washboard frequency” ω of the moving vortex lattice in untwinned YBa2 Cu3 O6.93 may be observed through mode-locking to an externally applied ac current of frequency ωext. The interference between ω and ωext results in jumps in the dc current-voltage characteristics when ω and ωext are harmonically related1. The interference effect disappears in the vortex liquid state. The Hall conductivity σxy below Tc in YBCO contains contributions2 from a positive quasiparticle (qp) term (∼H) and a negative vortex term (∼1/H). The qp term is surprisingly large well below Tc and implies a large gap anisotropy and a long qp mean free path (mfp). The thermal Hall effect3 κxy is closely related to the qp σxy; κxy is produced by asymmetric scattering of qp by pinned vortices. The qp mfp at H = 0, extracted from σxy and extended to low T by κxy, increases remarkably from 90 Å at Tc to more than 0.5μm at 22 K.
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  • 58
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    Journal of low temperature physics 105 (1996), S. 377-382 
    ISSN: 1573-7357
    Keywords: 74.20.Mn ; 25.40.Fq ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Key features of Inelastic neutron scattering experiments in YBCO-based cuprates are discussed. We underline the importance of precise oxygen content determination in samples having similar TC as well as the resolution configuration used. This may explain the apparent contradictory results recently obtained by different groups.
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  • 59
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    Journal of low temperature physics 105 (1996), S. 773-778 
    ISSN: 1573-7357
    Keywords: 78.30.Hv ; 74.72.Bk ; 74.25.Gz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Dense polycrystalline samples of YBa2Cu3O7−δ with a high degree of c-axis texture in the plane of the sample were prepared by magnetic alignment. The c-axis infrared reflectivity was measured between 300 and 6K on polished surfaces. Spectra compare well with measurements on single crystals indicating that magnetically aligned samples are a reliable alternative to single crystals for c-axis measurements.
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  • 60
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    Journal of low temperature physics 105 (1996), S. 483-488 
    ISSN: 1573-7357
    Keywords: 74.20.De ; 74-50.+r ; 74.72.Bk ; 74.62.Bf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A macroscopic symmetry group describing the superconducting state of an orthorhombically twinned crystal of YBCO is introduced. This macroscopic symmetry group is different for different symmetries of twin boundaries. Josephson tunneling experiments performed on twinned crystals of YBCO determine this macroscopic symmetry group and hence determine the twin boundary symmetry (but do not experimentally determine whether the microscopic order parameter is primarily d- or s-wave). A consequence of the odd-symmetry twin boundaries in YBCO is the stability of 1/2 Φo vortices at the intersection of a twin boundary and certain grain boundaries.
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  • 61
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    Journal of low temperature physics 105 (1996), S. 681-686 
    ISSN: 1573-7357
    Keywords: 74.25.Fy ; 74.25.Ha ; 74.40.+k ; 74.50.+r ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we summarize some of our theoretical results for the paraconductivity and for the fluctuation-induced in-plane magnetoconductivity in the weak magnetic field limit of layered superconductors with several interlayer separations. Also, we briefly discuss the existing experimental data obtained in untwinned Y Ba2Cu3O7-δ crystals.
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  • 62
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    Journal of low temperature physics 105 (1996), S. 743-748 
    ISSN: 1573-7357
    Keywords: 74.72.Bk ; 74.25.Gz ; 74.62.Dh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Zn-substitution effects on the c-axis optical spectra have been investigated for highly oxygenated YBa2 Cu3Oy crystals with y = 6.88 – 6.92. In the normal state, the Zn-substitution does not affect the high frequency conductivity but changes the ω-dependence of the scattering rate at low frequencies, leading to the increase in the dc resistivity in the c-direction. In the superconducting state, we observed a pronounced effect of Zn-substitution that a large number of unpaired carriers form a Drude-like absorption band within the gap, keeping the maximum gap amplitude unchanged. The missing area which gives the superfluid density is found to correlate with Tc.
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  • 63
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    Journal of low temperature physics 105 (1996), S. 779-784 
    ISSN: 1573-7357
    Keywords: 74.25.Gz ; 74.72.Bk ; 78.30.Er ; 63.20.Kr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Performing optical reflectivity measurements with the electric field vector parallel to the c-axis of Zn-substituted, oxygen deficient YBa2Cu3Oy single crystals, we find a strong Zn-substitution effect on the anomaly of the inplane oxygen bending mode at 320 cm−1 and the new absorption band at 450 cm−1, which are observed in underdoped, non-substituted crystals. Contrary to that, the low-frequency suppression of the conductivity is almost not affected. We conclude that the phonon anomaly and the absorption band are related to each other, but that the suppression of the conductivity is an independent phenomenon. Moreover, the present work could be strong evidence for a model where some phonons couple to antiferromagnetic fluctuations at the (π, π)-point leading to anomalous behaviour of these phonons when a spin gap opens.
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  • 64
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    Journal of low temperature physics 105 (1996), S. 1099-1104 
    ISSN: 1573-7357
    Keywords: 74.25.Bt ; 74.60.Ge ; 74.72.Bk
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    Topics: Physics
    Notes: Abstract High resolution adiabatic specific heat experiments on YBa2Cu3O7−δ (0≤δ≤0.05) are performed in magnetic fields from 0 to 14 T (B∥c and B⊥c). In a 0.3 gram, twinned crystal with strong pinning, a step is consistently observed at the melting temperature Tm of the vortex solid up to a critical point that depends on δ. The field Bm and step temperature Tm obey the relation Bm=Bmo(δ)(1−Tm/Tc)≈4/3. The anisotropy of Bm and that of the upper critical field Bc2 are found to be equal. Alternatively, in a 18 mg, twinned crystal of high purity with low pinning, first-order-like specific heat peaks are observed on the melting line from 8 to 14 T. The entropy under these peaks is ≈0.5 kB /vortex/bilayer. These characteristic features are attributed to the melting of a vortex glass in the former case and that of a vortex lattice in the latter case.
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  • 65
    ISSN: 1573-7357
    Keywords: 76.60.Ge ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The interplane (cb) and intraplane (ab) anisotropy of untwinned YBa2 Cu307 single crystals has been investigated by means of the torque magnetometry. To extract the reversible and irreversible components, the torque was measured as a function of increasing angle as well as decreasing angle. The interplane irreversible torque Γirr shows two-fold peaks at θc =90 ° and270 ° (of half width11 ° at77 K) due to the well-known intrinsic interplane pinning. A novel intrinsic pinning has been discovered in the intraplane irreversible torque, i.e., Γirr shows four-fold peaks of half width20° at77 K when θa =0 °, 90 °, 180 ° and270 °. We argue that the intrinsic intraplane pinning comes from the four-fold nature of the gap parameter.
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  • 66
    ISSN: 1573-7357
    Keywords: 74.60.Ge ; 74.72.Bk
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    Topics: Physics
    Notes: Abstract Real part of the ac susceptibility X′1 of an untwinned YBa2 Cu3O7 single crystal jumps at the onset temperature in the narrow width (0.1 K in 0.7 T), suggesting the first-order melting transition. A sharp X′1 dip and a sharp X″ peak can be interpreted as synchronous trapping of vortices due to lattice softening prior to melting. At lower temperatures, the X′1-X″1 chart shows a single-parameter behavior while the melting occurs as a strong deviation from this.
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  • 67
    ISSN: 1573-7357
    Keywords: 74.25.Fy ; 74.40.+k ; 74.60.Ge ; 74.72.Bk
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    Topics: Physics
    Notes: Abstract Pinning by point-like defects and twin boundaries in single-crystalline YBa2Cu3O7−δ has been investigated by measuring resistance and current-voltage characteristics in fields up to 5 T. A number of untwinned and twinned samples with different densities of point-like defects were studied. The experimental results are compared within the framework of vortex-entanglement.
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  • 68
    ISSN: 1573-7357
    Keywords: 73.50.Jt ; 73.5O.Pz ; 74.72.Bk ; 74.76.Bz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on in-situ resistivity and Hall-effect studies of partially oxygen-depleted YBa2Cu3Ox thin films during white light illumination. The measurements were performed at various temperatures between the superconducting transition and room temperature. At all temperatures the resistivity and the Hall coefficient decreased as a function of the illumination time. The Hall number pH and the Hall mobility μH, calculated within a simple one-band model, showed an increase of pH during the illumination without a saturation. At low temperatures, μH behaved similarly to pH. At 200 K, however, μH became constant after several hours of illumination, while at 260 K and 290 K, we observed a short increase of μH followed by a long-term decrease. From the different time dependences of μH and pH, we conclude that two mechanisms contribute to the photodoping effect. Additionally, we observed that after termination of the illumination at 290 K the photodoped values of pH and μH relaxed with substantially different time constants.
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  • 69
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    Journal of low temperature physics 105 (1996), S. 1129-1134 
    ISSN: 1573-7357
    Keywords: 74.60.Ge ; 71.20.−b ; 74.50.+r ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Scanning Tunneling Spectroscopy (STS) measurements have been carried out on the high Tc superconductor (HTS) YBa2Cu3O7−δ (YBCO). Using very high quality single crystals as well as hard tips, we obtained differential conductance spectra which showed various conductance features in agreement with other spectroscopic techniques. The reproducibility of our spectra allowed us to map for the first time the vortex lattice on a HTS using a STS technique1. The vortices are arranged in a short range order oblique lattice, while the cores of the flux lines show an anisotropic shape. These observations can be related to the in-plane anisotropy of YBCO.
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  • 70
    ISSN: 1573-7357
    Keywords: 74.25.Fy ; 74.40.+k ; 74.60.Ge ; 74.72.Bk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Magnetotransport measurements on a clean, untwinned YBa2Cu3O7−δ single crystal show that the vortex dynamics at temperatures just below the vortex lattice melting transition are highly dependent on the type of modulation of the probing current. While in the case of DC current the flux flow is disordered, the “shaking” of the vortex lattice by a square-wave current leads to a more uniform vortex motion. A small asymmetry (∼10%) in the durations of the positive and negative parts of the square-wave period induces periodical oscillations of the voltage response amplitude. The period of oscillations (∼100 s) is the same order of magnitude as the time needed for vortices to cross the sample (transit time). We relate the observed voltage oscillations to a periodically ordered vortex motion.
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  • 71
    ISSN: 1573-7357
    Keywords: 74.50.+r ; 74.72.Bk ; 74.76.Bz ; 85.25.Cp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Measurements of the field-modulated critical currents of cuprate thin film microbridges on tricrystal substrates are reported. Two central peaks of equal height are observed in the field-dependent critical currents of YBCO tricrystal microbridges. However, the critical current is nonvanishing at zero field for YBCO, consistent with an orthorhombically distorted d-wave order parameter. An ion-irradiated YBCO tricrystal microbridge has also been measured, and has been found to exhibit more ideal dx2−y2-like behavior with increasing irradiation dosage.
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  • 72
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    Journal of low temperature physics 105 (1996), S. 1421-1426 
    ISSN: 1573-7357
    Keywords: 74.72.Bk ; 74.60.Jg ; 74.80.Bj
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The preparation of a long superconducting Y123 filaments is developed by using solution spinning for the precursor of the oxide. Long precursor filaments are prepared by dry spinning with a starting homogeneous aqueous PVA solution containing Y, Ba and Cu acetates. The as-drawn filament with 250 μm in diameter and 300 mm in length is pyrolyzed and partial-melted by using a tube furnace with a constant heating zone of 500 mm. A superconducting filament of 60 μm in diameter and 200 mm in length with high Jc of more than 104A/cm2 at 77 K and 0 T is obtained by controlling the partial melting.
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  • 73
    ISSN: 1572-9605
    Keywords: Y0.4Pr0.6Ba2−xCaxCu3O7−δ ; superconductivity ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Y0.4Pr0.6Ba2−xCaxCu3O7−δ polycrystalline samples were prepared and investigated. The Ca substitution led to a structural variation toward tetragonal symmetry, possibly due to the structural modification within the Cu(1)O layer. Superconductivity and metallic conduction were recovered whenx≥0.2, giving one more evidence for the existence of the ion-size effect at the Ba site.
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