Polarized IR and Raman spectra, temperature dependence of phonons and lattice dynamic calculations for M′₂M″Ge₂O₇ pyrogermanates (M′ = Sr, Ba; M″ = Mg, Zn)

Abstract

O 7 were measured. The temperature dependence of phonons was studied in the range 4-295 K. The discussion of the results is based on the factor group approach for the tetragonal P42 1 m (D 3 2d ) space group with Z = 2. The discussion of the internal vibrations of the Ge 2 O 7 unit and external modes is made on the basis of the literature data and phonon calculations. The results obtained for the spontaneous Raman scattering were used in the discussion of the stimulated Raman spectra of the studied materials.

Experimental and Theoretical Investigations on Structural and Vibrational Properties of Melilite-Type Sr2ZnGe2O7 at High Pressure and Delineation of a High-Pressure Monoclinic Phase

“…Table 5). 2,53 It can be mentioned here that we have observed several new modes not previously reported at ambient conditions; however, some of them could not be observed in the DAC experiments at higher pressures. The evolution of RS spectra of phases.…”

“…2,48 Since the other high-frequency mode at 800 cm -1 corresponds to the other A 1 mode, Table 4 imposes that this mode must be assigned to the ν as (GeO 3 ) mode, which is opposite to the assignment in previous works. 2,53 As regards the bridge Ge-O-Ge modes, the symmetric stretching mode ν s (Ge-O-Ge) has been assigned to the theoretical A 1 and B 2 modes near 500 cm -1 . The A 1 mode is responsible for the Raman mode at 528 cm -1 in good agreement with previous literature.…”

Many-phonon stimulated Raman scattering and related cascaded and cross-cascaded χ(3)-nonlinear optical effects in melilite-type crystal Ca2ZnSi2O7

“…It could be further subdivided into (see, e.g. [10,39] [41][42][43]). In the crystal these modes will give rise to Γ int = 7A 1 + 4A 2 + 4B 1 + 7B 2 + 10E internal modes.…”

Synthesis and structural study of a new group of trigermanates, CaRE2Ge3O10(RE = La–Yb)

“…This also features the vibrational spectra of the silicates and germanates comprising the ijSi 3 O 10 ] 8− and ijGe 4 O 12 ] 8− anions, respectively. While the symmetric GeOGe stretchings are not influenced by the deformation contribution in the spectra of germanates with the Ge 2 O 7 pyrogroups, 51,52,55 this effect becomes apparent in vibration motions of the Ge 3 O 10 unit similar to Si 3 O 10 in silicates. However, the bands associated with ν s IJGeOGe) are shifted to 541 cm −1 and 536 cm −1 in the spectra of CaLa 2 Ge 3 O 10 , and are represented as weak infrared bands and Raman lines, respectively (Fig.…”

“…In the vibrational spectra of many isostructural series of lanthanide-containing antimonites, arsenates, germanates, phosphates and others, the bands are slightly displaced to higher wavenumbers with unit cell dimensions decreasing due to the phenomenon of lanthanide contraction. 51,54,55 In their turn, the ν as IJGeOGe) and ν s IJGeO 3 ) vibrations involve the motions of the Ge atom in the central tetrahedron GeIJ2)O 4 of the Ge 3 O 10 unit, which are found to be the most sensitive to variation of the Ge-O-Ge bond angle. The main reason is the presence of the above considered morphotropic transitions occurring between the Gd-Eu and Pr-La compounds (Fig.…”