Identification of the nature and mechanism of the zinc doping effect on the normal-state properties of the YBa2Cu3Oy system by a quantitative analysis of the thermopower and Nernst coefficient

Abstract

In this paper, we present the results of an experimental study of the temperature dependences of the thermopower, S, and the Nernst coefficient, Q, in samples of the YBa₂Cu_3-xZn_xO_y system with zinc content varying over a wide range. It is shown that, despite the fact that zinc doping has a very slight effect on the absolute values of the transport coefficients at T = 300 K, an increase in its content throughout the entire doping range studied leads to a consistent modification of the S(T) dependences, the nature of which is atypical for the cases of other cation substitutions in the YBa₂Cu₃O_y system. By analyzing the experimental results within the framework of the narrow-band model, we determined the values of the parameters characterizing the energy spectrum structure and charge carrier system properties in samples of different compositions, and then discussed their variations with increasing zinc content. The obtained calculation results clearly show that zinc substituting for the plane copper directly affects the normal-state energy spectrum of the YBa₂Cu₃O_y system, and also make it possible to explain all the observed specific features of the behavior of the transport coefficients in the studied system.