Hysteretic phase transition in Y1Ba2Cu3O7−x superconductors

H. M. Ledbetter; S. A. Kim

doi:10.1103/PhysRevB.38.11857

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Hysteretic phase transition in Y1Ba2Cu3O7−x superconductors

H. M. Ledbetter, S. A. Kim

DOI 10.1103/PhysRevB.38.11857 · Physical Review B

T1

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Abstract

We studied ultrasonic-wave velocities, both longitudinal and shear, in Y1Ba2Cu3O7−x, between 5 and 295 K, during both cooling and warming. Both waves, especially the longitudinal, show thermal hysteresis. The results suggest a hysteretic phase change that occurs between 160 and 70 K during cooling and between 170 and 260 K during warming. This phase-change hypothesis explains anomalies in several physical properties. The phase change agrees with thermodynamic-instability predictions. We confirmed the hysteresis in Ho-Ba-Cu-O, where it is smaller than in Y-Ba-Cu-O, and in Eu-Ba-Cu-O, where it is larger. In a companion perovskite, BaTiO3, we observed zero hysteresis. At Tc, 91 K, sound velocities show no measurable change in either magnitude or slope. This continuity disputes the current popular view that, contrary to thermodynamics, elastic stiffness increases upon cooling through Tc into the superconducting state. We believe that stiffening results from the usual thermal effects after a phase transformation from a stiffer phase.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Y1Ba2Cu3O7-x Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	91.2	Pressure not reported	unknown