The Eu1+xBa2−xCu3Oy system: oxygen content, phase transitions, point defect equilibria, and charge carriers

Abstract

Single phase Eu_1+xBa_2−xCu₃O_y materials with x = 0, 0.2, and 0.4 have been investigated with electrical conductivity and oxygen non-stoichiometry measurements at high temperatures (723–1073 K) and under various oxygen partial pressures. EuBa₂Cu₃O_y is an intrinsic semiconductor for 6<y<6.18, with a band gap close to 1 eV; for higher values of oxygen stoichiometry the crystal–gas equilibrium injects holes of different nature and mobility as extrinsic doping increases. This paper shows that the hole injection sequence and the variation of charge transport properties with different extrinsic and intrinsic doping levels can be effectively described by a quasi-chemical equilibrium approach if the particular features of the HOMO bands are considered. When the whole series of compounds is written as Eu_1+xBa_2−xCu₃O_6+x/2+z, the high temperature conductivity of the solid solutions is practically independent of x and shows a parallel dependence on oxygen excess z.