Massive transformation in Gd2O3-Bi2O3 ceramics

Gd2O3-doped Bi2O3 polycrystalline ceramic samples containing between 10 and 26 mol% Gd2O3 were fabricated by pressureless sintering of powder compacts. As-sintered samples were cubic (CaF2 structure), The cubic solid solutions underwent transformation to a rhombohedral phase when annealed at lower temperatures, Under certain conditions, the cubic phase fully transformed to the rhombohedral phase of the same composition, and the kinetics were thermally activated. This suggested that the cubic --> rhombohedral transformation was a massive transformation, The transition temperatures for the occurrence of a massive transformation were experimentally determined by measuring the conductivity as a function of temperature, as well as by measuring growth rate of the rhombohedral precipitates as a function of temperature, The activation enthalpy for interface motion was measured to be similar to 200 kJ/mol for the samples studied, The kinetics of cubic --> rhombohedral transformation could be described by the Johnson-Mehl-Avrami equation.