Preparation of Europium and Gadolinium Hafnates with Pyrochlore Structure Using Microwave Radiation

A method for obtaining europium and gadolinium hafnates with the general formula Eu_2–xGd_xHf₂O₇ at x = 0–2 using microwave radiation is considered. The influence of the duration of microwave treatment and the temperature of subsequent calcination on the phase composition of europium and gadolinium hafnate powders is investigated. The optimum microwave treatment time for powder systems that ensures the maximum content of europium hafnate and gadolinium hafnate in the phase composition of the material is established. Deviations from the found optimal duration of microwave exposure result in samples containing phases of individual oxides of the initial metals, namely, hafnium dioxide and rare earth element oxides. Heat treatment at 1350°C intensifies the process of ordering the crystal structure, facilitating the transition from the metastable fluorite phase to the stable pyrochlore phase. This conclusion is supported by the calculated unit cell parameters of Eu_2–xGd_xHf₂O₇ compositions at x = 0 and 2 that underwent heat treatment at 1200–1450°C. In systems with x = 0.5–1.5 annealed at 1500°C, the dependence of the structural type in which they crystallize on the duration of microwave treatment is determined.