Raman Spectra of Crystalline Double Calcium Orthovanadates Ca10M(VO4)7 (M = Li, K, Na) and Their Interpretation Based on Deconvolution Into Voigt Profiles

Equation of State and Amorphization of Ca9R(VO4)7 (R = La, Nd, Gd): A Combined High-Pressure X-ray Diffraction and Raman Spectroscopy Study

“…The bands at similar energies are typical for other orthovanadates, containing rare-earthsa broad review is available at ref . The large breadth of the Raman peaks is typical for whitlockite-related calcium vanadates, which is due to occurrence of nonequivalent atomic sites, with cations having different coordination spheres in the Ca-whitlockite structure …”

“…(polarized spectra), 16 and a set of alkali metal-containing TCV-Ca 10 M(VO 4 ) 7 (M = Li, Na, K). 38,55 In particular, the main peaks for all these crystals belong to two groups of bands; the widest referred ranges contain wavenumbers ∼50−500 cm −1 and 700−1000 cm −1 . Going into more detail, the lines at the low-frequency region are generally attributed to O−V−O bending modes, translational VO 4 oscillations, and Ca 2+ -ions displacements, whereas the high-frequency modes are related to V−O stretching bands and, in case of rare-earth-doped TCV, to the V−O−R chain vibrations (positioned at ∼880−910 cm −1 , as reported for the Ca 9 Nd(VO 4 ) 7 crystal).…”

“…The large breadth of the Raman peaks is typical for whitlockite-related calcium vanadates, which is due to occurrence of nonequivalent atomic sites, with cations having different coordination spheres in the Ca-whitlockite structure. 38 Opposite shift in Raman peaks with applied pressure is usually attributed to a phase transitionhere observed for Ca 9 R(VO 4 ) 7 at pressures of ∼9−11 GPa. The transition can take place to an amorphous or a new crystalline phase.…”

“…Among those crystals of composition and structure related to the β-TCP or TCV, for which some Ca sites are partially occupied by rare earths, the Raman spectra have been reported for Ca 3–3 x Nd 2 x (XO 4 ) 2 (X = P, V) in a broad temperature range, as well for Ca 9 Nd­(VO 4 ) 7 and Ca 3–1.5 x – y Eu x Cu y (VO 4 ) 2 at ambient conditions. , In the latter case, a reversible high-temperature phase transition has been reported . For several vanadate whitlockites, namely, for TCV and Ca 10 M­(VO 4 ) 7 (M = Li, Na, K), the factor group analysis has been performed. To the best of the authors’ knowledge, no high-pressure XRD and Raman spectroscopy investigations have been reported for any Ca 9 R­(VO 4 ) 7 materials.…”

“…16,37 In the latter case, a reversible high-temperature phase transition has been reported. 36 For several vanadate whitlockites, namely, for TCV 21 and Ca 10 M(VO 4 ) 7 (M = Li, Na, K), 38 the factor group analysis has been performed. To the best of the authors' knowledge, no high-pressure XRD and Raman spectroscopy investigations have been reported for any Ca 9 R(VO 4 ) 7 materials.…”