Physico-chemical nanomaterials science
New mixed orthovanadates La1-xRxVO4 as perspective materials for optoelectronics application
V.M. Hreb, A.M. Tupys, L.O. Vasylechko
Lviv Polytechnic National University, Lviv, Ukraine
E-mail: wasiahreb@meta.ua
Rare earth orthovanadates RVO4 with monazite and zircon type of structures have been widely used as laser host materials and optical polarizers, gas sensors, thin film phosphors and catalysts.
New mixed orthovanadates La1-xRxVO4 (R=Pr, Nd, Sm, Gd, Tb, Dy) were prepared by solid state reaction technique. Stoichiometric amounts of initial oxides (La2O3, Pr6O11, Nd2O3, Sm2O3, Gd2O3, Tb2O3, Dy2O3) and NH4VO3 were carefully mixed in agate mortar and heat treated in air at 1073-1173 K for 5-10 hours. Single phase purity of LaVO4-based orthovanadates was achieved by different temperature regimes, which were used for the annealing of the corresponding vanadates. According to X-ray powder diffraction examination, the La-richest La0.9Pr0.1VO4 and La0.9Nd0.1VO4 samples adopt monoclinic monazite-type structure, whereas the tetragonal zircon type of structure is inherent for La0.3Pr0.7VO4, La0.3Nd0.7VO4, La0.5Sm0.5VO4, La0.7Gd0.3VO4, La0.3Gd0.7VO4, La0.5Tb0.5VO4 and La0.5Dy0.5VO4 materials. Consequently, full profile Rietveld refinement was performed in P21/n and I41/amd space groups, respectively. Obtained structural parameters agree well with the lattice parameters for the parent LaVO4 and RVO4 compounds, thus proving formation of two type of solid solutions with monoclinic and tetragonal structures in LaVO4–RVO4 (R=Pr, Nd, Sm, Gd, Tb, Dy) pseudo-binary systems. Figure below demonstrates evolution of unit cell dimensions of tetragonal La1-xRxVO4 vanadates vs ionic radii of R-cations.

Figure. Lattice parameters and unit cell volumes of tetragonal La1-xRxVO4 series in a comparison with the literature data for the parent RVO4 compounds as a function of the radii of R3+ ions.	

Acknowledgements. The work was supported in parts by the Ukrainian Ministry of Education and Science under Project N 0118U000264 and ICDD Grant-in-aid program.