THE RELATION BETWEEN TRANSPORT-PROPERTIES AND OXYGEN STOICHIOMETRY IN YBA2CU3-XMXO7-DELTA (M=TI-4+ AND CR-3+)

The room temperature resistivity and thermopower of superconducting samples of substituted YBa2Cu3O7-delta (YBCO) having various dopant concentrations (x) are measured. Resistivity measurements are also made on samples prepared in pure oxygen and quenched from 950-degrees-C. The data on resistivity (rho) and thermopower (S) are correlated with the dopant concentration and the oxygen content. It is shown by curve fitting of a simple equation that a discontinuity in rho - alpha-x or S - alpha-x (where alpha is a constant) versus oxygen content occurs in the same region where a minimum in room temperature resistivity and thermopower are observed.