ELASTIC AFTEREFFECT STUDY OF THE FERROELASTIC TETRAGONAL-ORTHORHOMBIC PHASE-TRANSITION IN YBA2CU3OX

YBa2Cu3Ox compounds exist in tetragonal and orthorhombic structures. The transition between these structures is a ferroelastic order-disorder phase transformation, caused by a spatial redistribution of the O atoms in the Cu(1) atomic plane. The diffusive jumps of the O, which lead to such a redistribution, induce an anelastic relaxation process. We show that this relaxation process exhibits, in the neighborhood of the tetragonal-orthorhombic phase transformation, a very large increase of both the relaxation strength and the relaxation time (critical slowing down), where the temperature behavior of both quantities is approximately described by a Curie-Weiss law. We discuss finally elastic aftereffect measurements on sintered YBa2Cu3Ox samples which demonstrate the distinct influence of the tetragonal-orthorhombic phase transformation on the relaxation strength and relaxation time.