Synchrotron powder XRD patterns of in the range from 3° to 23°. The pressure medium was helium. In (a), the lower and upper panels correspond to the compression and decompression processes, respectively. The peaks denoted with are from the Re gasket and ruby. In (b), three diffraction data picked up for discussion of the crystal symmetry of HP phase are presented. The calculated position under simple-cubic and simple tetragonal lattices are indicated with thick marks. The peaks denoted with and are, respectively, from the Re gasket and ruby , of which the calculated positions (Refs. 31–33) are denoted with thick marks.
Raman spectra of obtained for various pressures up to 33 GPa on compression and decompression processes. The perfect reversibility is found on the spectral change. Solid circles correspond to the guest Ba vibration in the large cage. For arrows denoting the spectra, see text. The pressure medium was argon.
Typical results of Rietveld analyses performed up to 33 GPa. Solid circles denote the experimental data; solid lines, the calculated patterns; the thick marks, the calculated peak position; the bottom curves, the differences between the observed and calculated pattern. The angle regions in which the strong gasket peak appears were omitted from the fitting range.
Pressure dependence of internal atomic coordinate parameters obtained by Rietveld refinements.
Cage structure of . The unit cell is represented by a cube drawn by solid lines. The Wyckoff sites (6c, 16i, and 24k) of the host atoms are indicated. Arrows shows the displacements for the 24k site induced by pressurization.
Pressure dependence of unit-cell volumes of , (Ref. 26), and (Ref. 21) normalized with those under the ambient condition. Symbols correspond to the experimental data, and lines the result of theoretical fitting with Murnaghan’s EOS.
Raman frequencies of as a function of pressure.
The vibration frequencies of Ba encapsulated in the large cages of the Ge clathrates against the guest-host distance. Solid squares and circles correspond to and , respectively. The straight line is a fitted line under the assumption of a linear function of the distance of the guest-host distance, using both the data in the range higher than 0.362 nm.
Typical results of Rietveld refinements for under high pressures. The space group is and atom positions are Ba(2a) 0,0,0; Ba(6d) 1/4,1/2,0; Ge/Ga(6c) 1/4,0,1/2; Ge/Ga(16i) ; and Ge/Ga(24k) .
Isothermal bulk moduli and its pressure derivative obtained by Murnaghan’s EOS.
Article metrics loading...
Full text loading...