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  • 1
    Electronic Resource
    Electronic Resource
    Shape of the Cu(2) NQR spectra in YBa2Cu3O7, TmBa2Cu3O7 and TmBa2Cu4O8 (1997)
    Springer
    JETP letters 66 (1997), S. 624-629 
    Details
    ISSN: 1090-6487
    Keywords: 76.60.Gv ; 74.72.Bk ; 74.72.Yg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a study of shape of the Cu(2) NQR spectra in YBa2Cu3O7, TmBa2Cum3O7, and TmBa2Cu4O8 compounds at temperatures of 4.2–300 K. The results of the quantitative analysis lead us to conclude that the shape of the Cu(2) NQR spectra in all the samples studied can be described in the framework of the “motional narrowing” model, which implies that the Cu(2) nucleus possesses two different NQR frequencies between which it can rapidly jump. The difference in frequencies seems to be related to the charge-stripe correlations in CuO2 planes resulting in a dynamical modulation of the electric field gradients at the Cu(2) nuclei.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567612
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  • 2
    Electronic Resource
    Electronic Resource
    Antiferromagnetism in hydrated 123 compounds (1999)
    Springer
    JETP letters 69 (1999), S. 792-797 
    Details
    ISSN: 1090-6487
    Keywords: 74.72.Bk ; 74.25.Ha ; 75.50.Gg ; 76.60.Gv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Copper nuclear quadrupole resonance and zero-field nuclear magnetic resonance (ZFNMR) studies of YBa2Cu3O6.5 show that a magnetic phase appears in underdoped 123 superconductors treated in ambient moist air. The studies give convincing evidence that the “empty” CuO chains play the role of easy water insertion channels. The reaction occurs first in ordered regions of the crystallites. The final product of the reaction is a nonsuperconducting antiferromagnetic compound characterized by at least two types of magnetically ordered copper ions, with ZFNMR spectra in the frequency ranges 46–96 and 96–135 MHz, respectively. Even for powder samples fixed in an epoxy resin, this reaction is found to have partially occurred after a few years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.568092
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  • 3
    Electronic Resource
    Electronic Resource
    Stripe motion in CuO2 planes of Y1−x Pr x Ba2Cu3O7 as observed from the Cu(2) quadrupole resonance (1997)
    Springer
    JETP letters 65 (1997), S. 821-827 
    Details
    ISSN: 1090-6487
    Keywords: 61.72.Hh ; 74.72.Bk ; 74.80.−g ; 76.60.Gv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The NQR spectra of copper in the compounds YBa2Cu3O7, TmBa2Cu3O7, and Y0.9Pr0.1Ba2Cu3O7 at temperatures of 4.2–200 K are investigated by a pulsed NQR technique at frequencies of 28–33 MHz. Quantitative analysis of the spectra shows that the shape of the “plane” Cu(2) spectra is well described by using a model of 1D correlations of the charge and spin distribution in the CuO2 planes (stripe correlations). In the undoped superconductors the charge-spin stripe structure moves fast in the CuO2 planes, but doping the YBa2Cu3O7 lattice with praseodymium slows this motion down.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567452
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  • 4
    Electronic Resource
    Electronic Resource
    Comparative studies of the NMR of thulium in Tm123 and Tm124 compounds: Evidence for structural and electronic phase separation (1996)
    Springer
    JETP letters 64 (1996), S. 398-403 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567210
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  • 5
    Electronic Resource
    Electronic Resource
    DSC investigation of oxygen subsystem in Ba-Y-Cu-O superconductors (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 1123-1137 
    Details
    ISSN: 1572-8943
    Keywords: Ba-Y-Cu-O superconductor ; DSC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Für eine Reihe von Verbindungen der allgemeinen Formel Ba2YCu3Oy und einem Sauerstoffgehalt vony=6.0....6.9 wurden mittels verschiedener Wärmebehandlungen bei 800–1200 K, gefolgt durch Abschrecken oder beim chemischen Sauerstoffentzug durch Einbringen der Probe in Diwasserstoff bei 470–490 K DSC-Untersuchungen durchgeführt. Wird die Probe in Stickstoff erhitzt, so behält sie ihren Sauerstoffgehalt bei und zeigt bei 450–850 K einen exothermen Effekt. Es wurde gezeigt, daß die Funktion ΔH(y) bei etwa y=6.5 ein Maximum erreicht. Kinetische Messungen zeigen, daß für diesen Effekt die diffusive Beweglichkeit der Sauerstoffatome im Gitter verantwortlich ist.
    Notes: Abstract DSC investigations have been performed for a series of compounds Ba2YCu3Oy with the oxygen content varying in the rangey=6.0...6.9 by means of various heat treatments at 800–1200 K followed by quenching, or through the chemical extraction of oxygen by placing the sample in dihydrogen at 470–490 K. The sample preserving a constant oxygen content during heating in nitrogen exhibited exothermal effects between 450 and 850 K. It has been shown that the ΔH vs. y function reaches maximum aty ≈ 6.5. Kinetic measurements have shown that the diffusive mobility of oxygen atoms in the lattice is responsible for these effects, viz. the Arrhenius and cooperative processes of reorganization in the non-equilibrium oxygen subsystem of the bulk.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01979174
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  • 6
    Electronic Resource
    Electronic Resource
    Anomalies of Glass Transition: Manifestation in fullerene core polystyrene stars (2000)
    Springer
    Journal of thermal analysis and calorimetry 59 (2000), S. 23-31 
    Details
    ISSN: 1572-8943
    Keywords: DSC ; fullerene ; glass transition ; star-like polystyrene ; segmental dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Segmental dynamics around Tg in the 4- and 6-arm fullerene (C60) core star-like polystyrenes with different preset arm lengths was studied by DSC as compared to that in the linear PS and PS/C60 blend. The ‘anomalies’ in glass transition behavior were found for the stars including both suppression and facilitation of segmental motion, and pronounced dynamic heterogeneity within a transition range. The results are interpreted in terms of breakdown of intermolecular cooperativity of segmental motions and PS-C60 interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010163307598
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