Micro-probe Raman spectroscopy for detection of inhomogeneities in YVO4 single crystals

Abstract

Several near quasicongruent undoped YVO₄ single crystals grown by the Czochralski (CZ) technique as well as near stoichiometric YVO₄ single crystals grown by the top‐seeded solution growth technique, were investigated by micro‐probe Raman spectroscopy using unpolarized argon–ion laser light. The line broadening effects of the Raman active mode at 379 cm⁻¹ indicate that all CZ grown crystals possess wider peak widths than near stoichiometric YVO₄. In the latter case a value of 9.23 cm⁻¹ was measured for full width at half‐maximum. Although the annealing process in O₂ can improve the oxygen stoichiometry in the originally slightly oxygen deficient CZ grown YVO₄ crystals, certain remaining peak broadening effects demonstrate a Y–V related stoichiometry problem by both lower (external) and higher frequency (internal) modes. Radial inhomogeneous distributions were observed in CZ specimens by the shift of external Raman modes at 157 and 162 cm⁻¹ frequencies. In addition, nonassigned low intensity extra Raman peaks appeared over 1000 cm⁻¹ frequencies in all CZ grown samples. The above detected changes in Y–V–O stoichiometry demonstrate a complex phase system around the homogeneity region of quasicongruent YVO₄ specimens and enable a more realistic and unified interpretation of the segregated defects and stoichiometry changes in CZ grown YVO₄ single crystals than previously available.