ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Structure-property predictions for new planar forms of carbon: Layered phases containing sp2 and sp atoms (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6687-6699 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Structure, thermodynamics, and electronic properties are predicted for a new low energy phase of carbon which contains planar sheets equally occupied by sp2 and sp carbon atoms. The isolated planar sheets have the same planar symmetry as do the layers in graphite (p6m) and can be formally viewed as resulting from the replacement of one-third of the carbon–carbon bonds in graphite by –C 3/4 C– linkages. This material, called graphyne, is predicted to have a crystalline state formation energy of 12.4 kcal/mol carbon, which appears to be much lower than for any carbon phase which contains acetylenic groups as a major structural component. Based on the major structural reorganization required for graphitization and the observed high temperature stability of known model compounds, high temperature stability is predicted for graphyne. While graphyne will have similar mechanical properties as graphite, it is predicted to be a large bandgap semiconductor (Eg=1.2 eV) rather than a metal or semimetal. Based on this bandgap and the known behavior of related conjugated polymers having linear structures, interesting nonlinear optical properties (including a large third-order susceptibility) are expected. Property aspects are also predicted for other previously uninvestigated carbon phases which are structurally related to graphyne. Finally, structural features of alkali metal charge–transfer complexes of graphyne, which are expected to be metallic, and of related carbon phases are predicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453405
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Synthesis and structure–property aspects of poly(carbon diselenide) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4492-4497 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Poly(carbon diselenide), (CSe2)x, is obtained as a black powder either by thermal polymerization of CSe2 solutions at high pressure, slow thermal polymerization under ambient conditions of neat CSe2, or photopolymerization of CSe2 solutions. X-ray diffraction measurements indicate that the as-prepared polymer is highly disordered and does not contain free crystalline or amorphous selenium. This result contrasts with the extensive formation of free selenium in the high pressure, high temperature polymerization of neat CSe2. The electrical conductivity is below 10−6 S cm−1, which is consistent with a band gap of ∼2 eV obtained by diffuse reflection spectroscopy. Details of the thermal properties, and the optical absorption, electron spin resonance, infrared absorption, Raman scattering, and extended x-ray absorption fine structure (EXAFS) spectra of the polymer are discussed. The EXAFS data clearly indicate that Se–Se bonds (but not Se chains) are present. The resonance-enhanced Raman and infrared absorption spectra are consistent with the presence of conjugated carbon–carbon and C=Se bonds, respectively. Based on these results, the structure indicated for (CSe2)x is the head-to-head polymer Se (parallel) [–Se–Se–C–C–]n, (parallel) Se rather than the head-to-tail polymer Se Se (parallel) (parallel) [–C–Se–C–Se–]n, proposed by previous workers. This polymer thermally decomposes above about 130 °C to form trigonal selenium as a by-product.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453808
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Conjugation length dependent transport in conducting polymers from a resistor network model (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7492-7504 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of conjugation length (L) upon electronic conductivity components of conducting polymers is derived using a generalized resistor network model. Results are obtained for polymers which contain a statistical distribution of defects which limit conjugation, as well as for regular copolymers which have a fixed phase relationship between interruptions in conjugation on neighboring chains. The short-conjugation-length limits of the derived equations are identical with those previously obtained by evaluating molecular aspects of charge transfer. More specifically, when interchain transport fully limits both chain-direction conductivity (σ1) and an orthogonal conductivity (σ2), the calculated electrical anisotropy is σ1/σ2=L2/6d2F, where d is the interchain separation in a hopping direction, and the product d2F is the mean square average projection of the interchain vector on the electric field direction. The present analysis extends predictive capabilities over the entire range from short conjugation lengths to infinite conjugation lengths. For long conjugation lengths terminated by effectively infinite barrier defects, σ1/σ1(∞) and σ2/σ2(∞) are calculated from the parameters which define polymer structure and, for the former ratio, the ratio of infinite chain conductivities parallel [σ1(∞)] and orthogonal [σ2(∞)] to the chains. A general relationship, appropriate for a still wider range of conjugation lengths, is derived between σ1/σ1(∞) and [σ2/σ1(∞)]1/2(L/d)/F1/2, where the geometrical parameter F is of order unity in directions of high σ2. Using this relationship for a polymer of known structure, the chain-direction electrical conductivity in the infinite-chain limit can be derived from measurements of σ1, σ2, and average conjugation length. Good agreement is obtained between the calculated and observed dependence of conductivity upon conjugation length for available polymers, in which bulk conductivity is limited by interchain hopping.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456183
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Effect of charge transfer on chain dimension in trans-polyacetylene (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2346-2348 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: X-ray diffraction measurements on all-trans-polyacetylene are consistent with a chain-axis length elongation upon donor doping (+0.026 A(ring) for lithium and +0.04 A(ring) for potassium) and a chain-axis length contraction upon acceptor doping (−0.010 A(ring) for iodine), where the changes refer to the length L of a C2H2 unit (2.457 A(ring) in the undoped polymer). These new experimentally derived results for heavily doped compositions, which ignore possible corrections for cell nonorthogonality in the lithium and iodine complexes, are similar to experimental results for graphite intercalation complexes and are consistent with theoretical predictions for doped polyacetylene. The meridional diffraction lines observed at L and L/2 for potassium-doped polyacetylene indicate that there is no lattice symmetry element which includes a translation operation of L/2 in the chain-axis direction. The observations are consistent with a structural model in which alkali–metal ions with an intracolumn spacing of 4.96 A(ring) are commensurate with the polymer chains for the composition (CHM0.125)x. The likely polymer chain-axis repeat length is 2L (i.e., C4H4) and a lattice symmetry element which includes a translation of L is expected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453115
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Structure of polyacetylene–iodine complexes (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2523-2530 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We confirm the existence of a 15 A(ring) period in iodine-doped polyacetylene and provide a new interpretation for this key feature as part of a general model for structural changes during iodine doping. The observed diffraction intensities for different samples suggest the existence of structures with two different types of dopant-containing layers: layers obtained by complete replacement of polyacetylene chains by iodine columns (F layers) and layers obtained by replacement of every other polyacetylene chain by an iodine column (P layers). The F layers in the heavily doped complex alternate with dopant-free layers of polyacetylene chains (U layers), corresponding to a (UF)n stacking sequence. The phase obtained at a lower dopant concentration, which provides the 15 A(ring) spacing, is attributed to a (UPUF)n stacking sequence. At still lower dopant concentrations, one obtains a (UP)n stacking sequence. This model, along with published Raman, Mössbauer, and photoelectron spectroscopy data, suggests that the ratio of I−5 to I−3 increases in going from P layers to F layers. Intense and monotonically decreasing, diffuse x-ray scattering suggests that vacancies of size ∼3 A(ring) are present, probably in iodine columns. A diffuse reflection at 3.1 A(ring), observed in all iodine-doped samples, is due to an average iodine–iodine distance in disordered columnar arrays. On the other hand, ordered arrays of iodine columns in oriented samples give rise to sharp meridional reflections. All ten observed reflections (down to 1.17 A(ring)) in one sample could be indexed based on a 33.8 A(ring) repeat corresponding to (–I−3–I−5–I−3–)n arrays. The observed diffraction pattern was calculated from this model without using any freely adjustable parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455046
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Structure and properties of polyaniline as modeled by single-crystal oligomers (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3955-3961 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A single-crystal charge–transfer complex of a phenyl-end-capped tetramer of polyaniline has been synthesized and studied along with a similar dimer of polyaniline. Structural, optical, and electrochemical studies of these oligomers in various oxidation states provide detailed information which has been used to model the structure of polyaniline and its evolution during electronic doping. These studies of the polymer and its oligomers suggest that the emeraldine salt form of the polymer (50% doping per nitrogen) is a preferred low-energy structure. The preference for this structure leads to phase segregation in doped compositions having average doping levels less than 50%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453844
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    On the question of metallic and superconducting poly(carbon diselenide) (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 4019-4027 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Polymerization of carbon diselenide, CSe2, at 5 kbar and ∼100 °C has been reported to give a metallic (CSe2)n ladder polymer that superconducts near 6 K at 220 kbar pressure. Using a variety of techniques we find that the material synthesized (showing essentially the same x-ray diffraction pattern as previously published) is not (CSe2)n but instead consists of a mixture of free, trigonal Se and an amorphous C–Se polymeric composition consistent with the formula (CSe0.5)n. Interestingly, possibly as a consequence of staged reactions during synthesis, the Se phase consists of a mixture of large, aggregated crystallites (∼600 A(ring) in diameter) melting at ∼220 °C and nonaggregated small crystallites (∼150–250 A(ring) in diameter) showing a broad melting transition with an endothermic maximum at ∼180 °C. Percolation of the C–Se polymeric composition probably provides the high observed electrical conductivity [σ(300 K)≈10–20 S cm−1 and σ(300 K)/σ (8 K)≈2.5] in the presently available samples. The previously reported high pressure superconductivity is probably associated with the free Se phase in the samples, since selenium is a known superconductor in the 6 K and 220 kbar range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450870
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Theoretical study of the electronic properties and crystal structure of poly(perinaphthalene): On the origin of high observed conductivities (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1316-1322 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Combining the quantum chemical valence effective Hamiltonian (VEH) technique and crystal packing methods, we have investigated the electronic properties and crystal structure of poly(perinaphthalene), PPN. The goal is to understand the origin of high conductivities observed for a pyrolysis product which contains PPN chains. VEH band structure calculations for an isolated PPN chain predict a band gap which is small, 0.44 eV. The highest occupied and lowest unoccupied (HOMO and LUMO) bands have a combined width of about 9 eV. Analogous calculations for poly(perianthracene), PPA, yield a band gap (2.26 eV) which is much larger than that calculated for PPN. The symmetries of the HOMO and LUMO bands provide an explanation for the band gap difference between PPN and PPA. Crystal packing analysis predicts the existence of two phases for PPN, a phase in which PPN molecules are arranged as overlapping dimer pairs and a nondimeric phase in which there is little intermolecular overlap. The observed diffraction patterns for PPN suggests the packing of overlapping molecules in a third type of structure, possibly stabilized by a degree of irregular reaction during synthesis. Quantum chemical calculations indicate that interchain overlap decreases the band gap of PPN, from the 0.44 eV isolated chain value, to 0.29 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449449
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Bi-Sr-Ca-Cu-O and Pb-Bi-Sr-Ca-Cu-O superconductor films via an electrodeposition process (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1932-1933 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel electrochemical process has been developed for the formation of superconducting films. Using this process, superconducting films of Bi2Sr2Ca1Cu2O8 and (Pb,Bi)2Sr2Ca1Cu2O8 have been formed. The process consists of simultaneously depositing the metallic constituents of the superconductor from a single electrolyte, and thermally oxidizing the resulting precursor film to form the superconducting phase. Application of −4 to −5 V vs Ag/Ag+ to a conductive cathode substrate, immersed in an electrolyte containing salts of all of the metals, reduces the metal cations causing them to deposit on the cathode as a metallic film precursor. Precursor films having desired stoichiometries were obtained by regulating the electrolyte bath composition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101500
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...