Pressure-induced zircon to monazite phase transition in Y1–хLaхPO4: First-principles calculations

Abstract

Density functional theory was used to study pressure-induced phase transitions of zircon to monazite in doped yttrium orthophosphate, Y_1–хLa_хPO₄, 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 Y_1–xLa_xPO₄, 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.