High‐pressure Raman study on type‐I germanium clathrate

Abstract

Raman scattering measurements of the type-I Ge clathrtate, Ba 8 Ge 43 , have been performed at 1 bar and room temperature, and under high-pressures up to 22 GPa. Because of vacancies which exist in Ba 8 Ge 43 , the Raman spectrum at 1 bar was found to be different from that of Si clathrate. Low-frequency vibrational modes associated with Ba atoms were found around 35 -75 cm -1 and the Ge-framework Raman bands were observed around 80 -150 cm -1 comparable to the typical clathrate Ba 8 Si 46 . For these regions, spectral shapes are very similar to that of Ba 8 Si 46 . However, for the region above 150 cm -1 , all the peaks were considerably weak in intensity, in contrast to Ba 8 Si 46 . In the data obtained at high pressures, the spectral changes were observed around 8.0 GPa and 22 GPa.

Clathrate guest atoms under pressure

“…However, the pressures applied in the Ba 8 Si 46 study were much higher ͑ϳ1.7-20 GPa͒ than used here for Ba 8 Ga 16 Ge 30 ͑0.9 GPa͒. In a recent study of Ba 8 Ge 43 ᮀ 3 it was likewise observed that all modes shift to higher energies with applied pressure, 32 but again the applied pressures were higher ͑2.6-22 GPa͒ compared with the pressure used in this study.…”

Pressure-induced structural transformation of clathrate Ge136 via ultrafast recrystallization of an amorphous intermediate

“…[9]). The high-pressure behavior of filled clathrates was studied, e.g., for Ba 8 Si 46 [10], Ba 7.5 Si 45 [11], Ba 8 Ge 43 [12], or Rb 6. 15 Si 46 [13], where pressure-induced amorphization (PIA) and polyamorphic transition were observed (for a review, see Refs.…”

Sur les phases de type clathrate du silicium et des éléments apparentés (C, Ge, Sn) : Une approche historique

“…Récemment, Fukushima et al ont réalisé une étude comparative de Ba 8 Si 46 et Ba 8 Ge 43 X 3 , ce dernier comportant dans son réseau d'accueil des lacunes ordonnées (paragraphe 3.1) impliquant la présence d'atomes de germanium triplement liés seulement[149]. Les spectres de diffusion Raman des deux clathrates sont très proches pour les fréquences inférieures à 200 cm À1 , mais diffèrent nettement pour les plus hautes fréquences en raison de la quasi-disparition dans le spectre du clathrate lacunaire de modes de vibrations nettement visibles pour le clathrate stoechiométrique.…”