MICRO-PROBE RAMAN-SPECTROSCOPY FOR DETECTION OF INHOMOGENEITIES IN YVO4 SINGLE-CRYSTALS

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 inves tigated by micro-probe Raman spectroscopy using unpolarized argon-ion laser light. The line broadening effects of the Raman active mode at 3 79 cm(-1) indicate that all CZ grown crystals posses 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 annealin g process in O-2 can improve the oxygen stoichiometry int he originall y slightly oxygen deficient CZ grown YVO4 crystals, certain remaining peak broadening effects demonstrate a Y-V related stoichiometry proble m by both lower (external) and higher frequency (internal) modes. Radi al inhomogeneous distributions were observed in CZ specimens by the sh ift of external Raman modes at 157 and 162 cm(-1) frequencies. In addi tion, nonassigned low intensity extra Raman peaks appeared over 1000 c m(-1) frequencies in all CZ grown samples. The above detected changes in Y-V-O stoichiometry demonstrate a complex phase system around the h omogeneity region of quasicongruent YVO4 specimens and enable a more r ealistic and unified interpretation of the segregated defects and stoi chiometry changes in CZ grown YVO4 single crystals than previously ava ilable. (C) 1996 American Institutes of Physics.