Thermal expansion behavior and high-temperature electrical conductivity of A2−xAx′Cu1−yCoyO4±δ (A = La, Pr; A′ = Pr, Sr) oxides with the K2NiF4-type structure

Three different compositional series of Pr-containing cuprates with the K2NiF4-type structure have been prepared by annealing at 1273 K, 48-90 h in air: with Cu on B-site only in formal oxidation state +2 (La2−xPrxCuO4, x = 0.1; 0.2; 0.4) (i), with partial replacement of Cu2+ by small (La2−xPrxCu1−yCoyO4±δ, 0.1 ⩽ x ⩽ 0.5; y = 0.05; 0.1) (ii) and large (Pr2−xSrxCu1−xCoxO4±δ, x = 0.5; 0.75) (iii) amount of cobalt. Partial replacement of Cu by Co, as in La2−xPrxCu1−yCoyO4±δ, leads to an increase of thermal expansion coefficients (TECs) in comparison with La2CuO4. Unusual high anisotropy of TEC along the a-(TEC(a)) and c-axes (TEC(c)) of the tetragonal unit cell is observed for Pr2−xSrxCu1−xCoxO4±δ, x = 0.5 and 0.75. TEC(c)/TEC(a) ratio increases with increasing amount of cobalt from 3.29 (x = 0.5) to 3.61 (x = 0.75). High-temperature electrical conductivity measurements at 298-1173 K in air reveal semiconductor-like behavior for all studied compositions with electrical conductivity values at 1173 K in air vary from 1.8 S/cm for La1.9Pr0.1Cu0.9Co0.1O4±δ to 5 S/cm for La1.6Pr0.4CuO4±δ and to 25 S/cm for Pr2−xSrxCu1−xCoxO4±δ, x = 0.5, 0.75.