Pressure-induced zircon to monazite phase transition in Y1–х La х PO4: First-principles calculations

Abstract

Density functional theory was used to study pressure-induced phase transitions of zircon to monazite in doped yttrium orthophosphate, Y1–хLaхPO4, for х = 0, 0.0625, 0.125. The pressures of the phase transition, the elastic moduli and the universal elastic anisotropy index were calculated. It was shown that with increasing lanthanum concentration in Y1–xLaxPO4, the transition pressure increases. According to the Birch–Murnaghan equation of state, this effect is associated with a decrease in the critical volume. The increased stability of the doped zircon phase compared to YPO4 is attributed to the more significant increase in the anisotropy and distortions of REO8 polyhedra and RE–O–P chains found for the optimized structures at critical volumes.