THE RELATIONSHIP BETWEEN THE FERROELECTRIC PHASE-TRANSITION NEAR T0=235-K IN YBA2CU3O7-X AND HIGH-TC SUPERCONDUCTIVITY - COMPARISON WITH THE POLARON THEORY OF PARDEE AND MAHAN

A variety of data summarized in this special issue imply that diverse experimental data, including specific heat, dielectric permittivity, and Raman sectra, can be interpreted as evidence for a structural phase transition near 235 K, probably from mmm to mm2 space group symmetry. In the present paper we emphasize the Raman results of Zhang et al. and of Rebane et al. (Sol. St. Commun. 65,487,1535 (1988)) and attempt to relate them to the high-temperature superconductivity changes near T = 235 K reported by Bhargava et al. (Phys. Rev. Lett, 59,1468 (1987)) as well as other phenomena near Tc. The phenomena at Tc and T0 bear a strong resemblance to those of sequential phase transitions in the polaron theory of Pardee and Mahan (J. Sol. St. Chem. 15, 310 (1975)). © 1990, Taylor & Francis Group, LLC. All rights reserved.