Isotopic Impurity Modes and Polariton Dispersion in Li₂GeO₃ Crystals

Abstract

Infrared reflection and Raman spectra of single crystals of 7Li,GA03 and 6Li,Ge03 containing 7.42 and 9.10% of 6Li and 'Li, respectively, are measured and the oscillator parameters ;LO, $TO, y~o ,and y r o determined using the Kurosawa dispersion relation. The experimental attenuated total reflection spectra are in good agreement with the calculated polariton dispersion curves. The resonance type interactions between parent and isotopic impurity deformation modes are interpreted; the behaviour of the corresponding phonons depends on their symmetry species.Les spectres infrarouge et Raman de monocristaux de 'LiGeO, et 6Li,Ge03, contenant 7,42 et 9,10% de 6Li et 'Li, respectivement, ont btB analyses e t les parametres ;LO, ;TO, y~o , et TO de l'oscillateur ont btb determines i partir de la relation de dispersion de Kurosawa. Les spectres obtenus par reflexion totale attbnube sont en bon accord avec les courbes de dispersion du polariton calculbes. Des interactions resonantes ont Ate mises en evidence entre modes de deformation de I'isotope preponderant et de l'impuretb isotopique ; le comportement des phonons correspondants est diffbrent suivant leur type de symbtrie.

Lattice dynamics calculations and temperature dependence of vibrational modes of ferroelastic Li2TiGeO5

“…Translations of Li + ions are also predicted to be observed near 416 (442) and 322 (303) cm −1 . The region of T (Li) modes predicted by our calculations is in good agreement with the previous studies of Li 2 GeO 3 where these modes were located in the 250-500 cm −1 region on the basis of isotopic substitution [10]. Translational motions of Ti 4+ and Ge 4+ ions are expected to contribute significantly to those IR modes which are observed at 296 and 227 cm −1 , respectively.…”

“…The remaining stretching modes correspond to vibrations of the O1 oxygen atom, which connects TiO 5 and GeO 4 polyhedra via a Ti-O1-Ge bridge. Vibrations of the Ge-O-Ge bridge were observed at 698 cm −1 for Li 2 GeO 3 [9,10] and near 800-860 cm −1 for Li 2 Ge 7 O 15 [11]. It is also worth noting that the calculations predict the presence of only one E u and two A 2u modes in the high-frequency region whereas two E u modes were observed in the reflection spectra (see tables 1 and 3).…”

In Situ Raman Spectroscopy and DFT Studies of the Li2GeO3 Melt Structure

“…Orel et al also analyzed the vibrations of the Li 2 GeO 3 crystal . Their results showed that the 36 lattice phonons (10A 1 + 8A 2 + 8B 1 + 10B 2 ) can be divided into 20 internal phonons (6A 1 + 4A 2 + 4B 1 + 6B 2 ) and 16 external phonons, which are subdivided into three acoustic phonons (A 1 + B 1 + B 2 ), 12 Li + ion translational phonons (3A 1 + 3A 2 + 3B 1 + 3B 2 ), and one [GeO 2 Ø 2 ] n chain librational phonon (A 2 ).…”