A DIFFUSE PHASE-TRANSITION IN SUPERCONDUCTING YBA2(CU1-XMNX)(3)O-7-DELTA (M=ZN, NI, CR) COMPOUNDS

Dielectric and magnetic behaviour of the YBa2(Cu(1-x)M(x))(3)O-7-delta (M=Zn, Ni, Cr and x less than or equal to 0.10) system was investigat ed. The results suggest a diffuse phase transition to a relaxer-type f erroelectric state. Taking into account the double-well model of high- temperature superconductivity and using double-well parameters from th e Abrahams-Kurtz-Jamieson (AKJ) relation for ferroelectric phase trans ition in oxide perovskite, the unrenormalizable barrier heights are ca lculated. The values could be related to an excitonic mechanism of sup erconductivity. Small anomalies observed in the static dielectric cons tants coincide with the Neel points of the corresponding nonsupercondu ctive phases in YBa2(Cu(1-x)M(x))(3)O-7-delta compounds.