HIGH-TEMPERATURE ELECTRICAL CHARACTERIZATION OF GA-BASED LAYERED CUPRATES

High-temperature electrical conductivity and Seebeck coefficient measu rements were performed on Single-CuO2-layer La1-xSr1+x CuGaO5 (x = 0.1 and 0.13) and double-CuO2-layer Y1-xCaxSr2 Cu2GaO7 (x = 0, 0.1, 0.2, 0.4). The solubility range in Y1-xCaxSr2 CU2GaO7 is Most likely 0 less -than-or-equal-to x less-than-or-equal-to 0.2, whereas, only the x = 0 .1 composition is stable in La1-xSr1+xCuGaO5. Carrier concentration is essentially independent of temperature and oxygen partial pressure in both systems. The defect structure is dominated by p = [AE(RE)'], whe re AE = alkaline earth and RE = La or Y. The conductivity, and therefo re the mobility, is activated for x = 0 and x = 0.1 in Y1-xCaxSr2Cu2Ga O7. Solid solubility limits and charge localization play major roles i n the establishment of superconductivity in these phases. (C) 1994 Aca demic Press, Inc.