Dopant Induced Stabilization of Metastable Zircon-Type Tetragonal LaVO4

5 years ago

Dopant Induced Stabilization of Metastable Zircon-Type Tetragonal LaVO4

Sri Sivakumar, Jitendra Kumar, Shilendra Kumar Sharma, Akshay Patel, Chandresh Kumar Rastogi, Raj Ganesh S. Pala, G. Parthasarathy

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 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 °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 La_1–xEu_xVO₄ (x = 0.0625–0.375) vis-à-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.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b04508

DOI: 10.1021/acs.jpcc.7b04508