Dopant Induced Stabilization of Metastable Zircon-Type Tetragonal LaVO4

Zircon-type tetragonal LaVO4 phase is a suitable host for luminescent lanthanide ions but exhibits poor stability and transforms to monazite -type monoclinic phase at elevated temperatures and pressures. Here, we have studied the effect of partial substitution of La3+ with Eu3+ ions on the phase stability of tetragonal LaVO4 using the temperature and pressure induced phase transformation characteristics. Experimentally measured activation energy required for the initiation of phase transformation is found to 77 increase with increasing europium content and suggests dopant induced stabilization of the. tetragonal phase. The critical pressure (P-c) and critical temperature (T-c) required for tetragonal to monoclinic phase transition increase with increasing Eu3+ ions concentration, values being T-c = 300, 500, and 600 degrees C and P-c = 2, 4, and 6.5 GPa for compositions x = 0, 0.025, and 0.05, respectively. The simulations based on density functional theory (DFT) support the P-c data, and.the decrease in the formation energy of tetragonal La1-x EuxVO4 (x = 0.0625-0.375) vis-a-vis monoclinic phase suggests improvement in its stability with increasing doping concentration. Further, the doped Eu3+ ions act as an optical probe and the observed variation in their luminescent characteristics is related to the structural transformation occurring due to pressure and heat treatment.