PHYSICAL AND CHEMICAL-PROPERTIES OF (Y1-XCAX) (BA2-XLAX)CU3O7-DELTA

The metallic conductivity of both the CuO2 sheets and the CuOx chains of YBa2Cu3O7-delta has been established. We have used double doping in (Y1-xCax)(Ba2-xLax)Cu3O7-delta to destroy the integrity of the CuO1-d elta chains while keeping constant the total oxidation state of the Cu -O array. A break-up of the chain segments allows us to establish the temperature dependence of the Seebeck coefficient, alpha(T), due to th e CuO2 sheets and, by difference, that of the Cu-1-delta chains in YBa 2Cu3O7-delta. We also show that double doping enhances significantly t he chemical stability of the superconductive phase. Tile origin of the chemical stability and of the behavior of alpha(T) is interpreted.