Raman spectroscopy of CaM²⁺Ge₂O₆(M²⁺ = Mg, Mn, Fe, Co, Ni, Zn) clinopyroxenes

Abstract

The Raman spectra of Ge‐clinopyroxenes CaM2+Ge2O6 (M2+ = Mg, Mn, Fe, Co, Ni, Zn), general formula M2M1T2O6, are reported for the first time. Their spectral features are discussed in comparison with corresponding Si‐pyroxenes. The vibrational wavenumbers of germanates may be roughly obtained by a scale factor of about ~0.8 by those of the corresponding silicates, due to the Ge‐Si mass difference. The main peaks in the germanate Raman spectra at ~850 and ~540 cm−1 may be related to Ge‐O tetrahedral stretching and chain bending, respectively; minor peaks between 200 and 400 cm−1 are ascribed to bending and stretching of the non‐tetrahedral cations. Within Ge‐pyroxenes, possible correlations between crystallographic parameters and the vibrational wavenumbers are investigated. The main stretching mode at ~850 cm−1 shows wavenumber changes with M2+ substitutions, but no simple correlation can be found with M2+ cation mass or size. On the other hand, the chain bending wavenumber linearly decreases with increasing ionic radius of the M2+ cation: the expansion of the M1 polyhedron reduces the chain kinking angle and the Ge‐Ge distances correspondingly increase. Copyright © 2015 John Wiley & Sons, Ltd.

Low‐temperature sintering of microwave ceramics with high Qf values through LiF addition

“…Therefore, the Raman spectra are almost identical in all samples. According to previous studies, the Raman shift at <300 cm −1 could be attributed to translations of SiO 4 tetrahedron, the peak at 300–450 cm −1 could be assigned to motions of the cations in the M(2) and M(1) sites that were related with tetrahedral chain motion and tilting tetrahedron. Moreover, the Raman shifts in the region of 225‐303, 360, 450‐600, 666, and 1011 cm −1 can be attributed to the O–Li–O bending and Li–O stretching vibrations, the O–Si–O vibrations, the stretching/bending modes of the Si–O–Si bonds, and O–Si–O stretching modes, respectively.…”

High-pressure crystallography and compression behavior of the alkali-scandium-germanate end-members LiScGe2O6 and NaScGe2O6

“…The most prominent bands in the wavenumber range 500-900 cm -1 can be assigned to the vibrational modes of the tetrahedral GeO 4 units [28]. They are similar to the equivalent SiO 4 modes reported for spodumene and related silicates exhibiting the pyroxene structure type [28,29], which are shifted to higher wavenumbers.…”

High‐pressure Raman spectroscopy of Ca(Mg,Co)Si2O6 and Ca(Mg,Co)Ge2O6 clinopyroxenes

“…In germanates, we find similar features albeit downshifted in energy . The strong peaks at ~670 and ~1010 cm −1 in silicates have their counterparts at ~550 and ~850 cm −1 in germanates, respectively . In germanates, the peak corresponding to that at about 1010 cm −1 in silicates is accompanied by a second peak at lower intensity.…”

“…Natural diopside, with composition CaMg 0.93 Fe 0.07 Si 2 O 6 , synthetic CaCoSi 2 O 6 and CaCoGe 2 O 6 single crystals were loaded in the diamond anvil cell for the experiments. CaMgGe 2 O 6 was available only as a polycrystalline material, and a few crystallites (average size 8–10 μm) were loaded in the P ‐chamber. Therefore, the absolute intensities of the Raman modes in CaMgGe 2 O 6 could be affected by the orientation of the crystallites.…”