Thermoanalytical and X-ray Diffraction Studies on the Phase Transition of the Calcium-Substituted La₂Mo₂O₉ System

An aqueous sol-gel preparation technique was applied for the synthesis of calcium-substituted lanthanum molybdate with the initial composition of La_2-xCa_xMo₂O_9-x/2. The influence of the substitution effect, which plays a crucial role in the formation of final ceramics, was investigated. The thermal behavior tendencies of phase transition at elevated temperatures from the monoclinic crystal phase to cubic as well as reversible transformation were identified and discussed in detail. It was proved that the phase transformation in the obtained mixture significantly depends only on the impurities' amount, while the partial substitution by calcium atoms above the value of x = 0.05 does not create a homogeneous multicomponent system for La_2-xCa_xMo₂O_9-x/2 composition.