Analysis of the possible reasons for the suppression of superconductivity in the Y1−xPrxBa2Cu3Oy system on the basis of thermoelectric power data

Abstract

The temperature dependence of the thermoelectric power in samples of Y 1− x Pr x Ba 2 Cu 3 O y ( x =0−0.6) is investigated. The principal parameters of the system of charge carriers are determined on the basis of an analysis of this dependence within a narrow-conduction-band model, and their variation with increasing praseodymium content is analyzed. It is found that an increase in x leads to a very weak increase in the electron filling and considerable broadening of the conduction band accompanied by strong localization of the charge carriers. It is concluded on the basis of a comparative analysis of the results obtained and data for the YBa 2 Cu 3 O y system in the case of aliovalent substitutions in the barium and copper sites that the valence of praseodymium in Y 1− x Pr x Ba 2 Cu 3 O y is very close to 3+. It is shown that there is a universal correlation between the effective width of the conduction band and the critical temperature following various cation substitutions in the Y-Ba-Cu-O system. It is concluded that the main reason for suppression of the superconducting properties of Y 1− x Pr x Ba 2 Cu 3 O y is the strong modification of the band spectrum caused by praseodymium.