Thermoelectric power of YBa₂Cu₃O_x in equilibrium with gas phases

Abstract

Thermoelectric power (TP) and electrical conductivity (EC) measurements were performed for YEa₂Cu₃O_x at 1128 K under controlled oxygen partial pressure varying between 50 and 10⁵ Pa. Three regimes are observed for the electrical properties. At low$p_{{\text{O}}_{\text{2}} } (< 1.6{\text{ }} \times {\text{ 10}}^{\text{2}} {\text{ }}{\text{Pa}})$ both TP and EC remain constant with$p_{{\text{O}}_{\text{2}} }$. In the medium range$(1.6{\text{ }} \times {\text{ 10}}^{\text{2}}< p_{{\text{O}}_{\text{2}} }< 7.6{\text{ }} \times {\text{ 10}}^{\text{3}} {\text{ Pa)}}$ sharp changes of both electrical parameters occur; TP changes sign from positive above 4×10² Pa to negative below this$p_{{\text{O}}_{\text{2}} }$ value. In the high$p_{{\text{O}}_{\text{2}} }$ region (>7.6×10³ Pa) TP vs log$p_{{\text{O}}_{\text{2}} }$ exhibits two slopes; 5.1 below 1.5×10⁴ Pa and 8.4 above this$p_{{\text{O}}_{\text{2}} }$ value. The slopes can be discussed in terms of the defect structure involving singly and doubly ionized oxygen vacancies below and above 7.6×10³ Pa, respectively.