Phase Stability of bulk (R0.8Ca0.2)Ba2Cu3O7-z (R = Lu and Y) Compounds

Polycrystalline samples of R0.8Ca0.2)Ba2Cu3O7-z (R = Lu and Y) were synthesized by a solid-state reaction route, and the phase stabilities were examined by heating at temperatures between 800 degree C and 900 degree C in various atmospheres. A comparative analyses of the x-ray diffraction data of the (Lu0.8Ca0.2)Ba2Cu3O7-z and (Y0.8Ca0.2)Ba2Cu3O7-z compounds showed that the 123 phase of both compounds is stable under heating in air and O2 of 1 atm. However, contrary to the (Y0.8Ca0.2)Ba2Cu3O7-z compound, the Lu0.8Ca0.2)Ba2Cu3Oz compound was found to become unstable when heated in the low oxygen partial pressure below about 8 %O2 in N2 , Considering the instability of parent LuBa2Cu3O2 compound, this result suggests that the phase stability of Lu-based 123 compounds is sensitive to both the composition and the oxygen partial pressure.