Anomalously Large Oxygen-Ordering Contribution to the Thermal Expansion of UntwinnedYBa2Cu3O6.95

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.

High Pressure Effects on Superconductivity

“…The ordering of oxygen vacancies at ambient pressure was also observed near optimal doping in YBa 2 Cu 3 O 6.95 , most notably in thermal expansion measurements [96]. Upon cooling from high temperature a glass-like transition with distinct anomalies in the thermal expansion coefficients around 280 K indicates the rearrangement of the oxygen ions.…”

Inhomogeneity of the intrinsic magnetic field in superconducting YBa2Cu3OXcompounds as revealed by a rare-earth EPR probe

“…The experimental values of parallel (g ║ ) and perpendicular (g ⊥ ) components of g-factors of The approaching of the EPR lines in parallel and perpendicular orientations to each other at T > T irr could be ascribed to the temperature dependence of the lattice parameters of YBaCuO [22] as well as to the demagnetizing effects. The detailed discussion of this is not in the scope of the present paper.…”

‘Fragile Superconductivity’: A Kinetic Glass Transition in the Vortex Matter of the High-temperature Superconductor YBa2 Cu3O7-δ

“…2) (These small temperature shifts could be accurately determined only because the anomaly at T c provided a close calibration point.). Both the history-dependent shape of the anomaly and the heating-rate dependence are typical for kinetic glass transitions [17][18][19][20][21] . We note that the large peaks in α(T) most likely are caused by magnetostrictive effects 22 as a result of macroscopic currents, which decay upon heating at the glass transition.…”

“…The thermal expansion was measured in a high-resolution capacitance dilatometer in the range 7-140 K in magnetic fields up to 11.4 T. The magnetization data were taken with a vibrating sample magnetometer in a constant field of 6 T. Both types of measurements were performed in a continuous cooling and heating mode with rates between ±2 and ±90 mK/s. These types of temperature scanning experiments are ideally suited to probe the kinetics of glass transitions, since the time scale of the experiment is directly proportional to the heating (cooling) rate [17][18][19][20][21] . In Fig.…”