title: Anomalously large oxygen-ordering contribution to the thermal expansion of untwinned YBa2Cu3O6.95 single crystals: A glasslike transition near room temperature
abstract: We present high-resolution thermal expansion data from 5-500 K of untwinned YBa2Cu3Ox (Y123) single crystals for x approximately 6.95 and x = 7.0. Large contributions to the thermal expansivities due to O ordering are found for x approximately 6.95, which disappear below a kinetic glasslike transition near 280 K. The kinetics at this glass transition is governed by an energy barrier of 0.98+/-0.07 eV, in very good agreement with other O-ordering studies. Using thermodynamic arguments, we show that O ordering in the Y123 system is particularly sensitive to uniaxial stress along the chain axis and that the lack of well-ordered chains in Nd123 and La123 is most likely a consequence of a chemical-pressure effect.
authors.affiliation: Forschungszentrum Karlsruhe, Institut fur Festkorperphysik, P.O. Box 3640, 76021 Karlsruhe, Germany.
authors.initials: P
authors.lastname: Nagel
authors.initials: V
authors.lastname: Pasler
authors.initials: C
authors.lastname: Meingast
authors.initials: AI
authors.lastname: Rykov
authors.initials: S
authors.lastname: Tajima