The structural and vibrational properties of ${\mathrm{Lu}}_{1.8}{\mathrm{Y}}_{0.2}\mathrm{Si}{\mathrm{O}}_5$ (LYSO) single crystals were investigated by means of Raman spectroscopy and x-ray diffraction measurements. Unit cell parameters and bond lengths were determined by Rietveld refinement of the collected x-ray diffraction powder spectra. By comparison with the vibrational spectra of the parent compounds ${\mathrm{Lu}}_2\mathrm{Si}{\mathrm{O}}_5$ and ${\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ and by using polarized Raman measurements, we propose the assignment of the principal vibrational modes of LYSO crystals. The strict connection of Raman spectra of the LYSO solid solution and of the pure lutetium and yttrium crystals, as well as the analysis of the polarized measurements, confirms that LYSO structure adopts the $C2∕c$ space group symmetry. The structural analogies of LYSO with the pure compound ${\mathrm{Lu}}_2\mathrm{Si}{\mathrm{O}}_5$ are further shown by means of high pressure Raman spectroscopy, and the possibility of considering the LYSO crystal analogous to the LSO structure with a tensile stress between 0.25 and $0.80\mathrm{GPa}$ is discussed.

• Received 6 February 2007

DOI:https://doi.org/10.1103/PhysRevB.76.054112