Density functional study of the phase stability and Raman spectra of Yb2O3, Yb2SiO5 and Yb2Si2O7 under pressure

Abstract

The phase stability and Raman spectra of Yb₂O₃, Yb₂SiO₅ and Yb₂Si₂O₇ under hydrostatic pressure are investigated using density functional theory calculations. The calculated energies of polymorphs of each compound show that the stable phases at zero pressure, viz., C-type Yb₂O₃, X₂-Yb₂SiO₅ and β-Yb₂Si₂O₇, exhibit a pressure-induced phase transition as compressive pressure increases, which is consistent with available experimental data. The theoretical Raman spectra at zero pressure are in good agreement with experimental results for the stable phases and can be used to identify each polymorph. Although the calculated pressure dependence of Raman peak positions of C-type Yb₂O₃ is overestimated compared to available experimental data, piezospectroscopic coefficients extracted from Raman peaks of X₂-Yb₂SiO₅ and β-Yb₂Si₂O₇ suggest that Raman spectroscopy can be used to measure stresses and strains in Yb silicates. Normal mode analyses reveal that characteristic Raman peaks of Yb silicates at frequencies above 600 cm⁻¹ are strongly associated with vibrations of Si–O bonds in Si_xO_y tetrahedral units.