Raman Scattering in Langasite-Family Crystals

Raman scattering spectra have been investigated in La3Ga5SiO14 langasite crystals with Cr and Fe impurities and La3Ga5.25Ta0.25Si0.5O14 crystalline solid solution. It is shown that all spectra contain a low-frequency peak near 110 cm–1. The La3Ga5.25Ta0.25Si0.5O14 crystal exhibits high-frequency peaks in the range from 1000 to 2000 cm–1, which are much stronger than the low-frequency peaks. The intensities of the Raman peaks recorded in the La3Ga5SiO14 crystal are close in the entire spectral range. The differences in the spectra of the ideal single crystal and solid solutions can be explained by the manifestation of additional modes in the solid solutions.