R. Lu et Am. Hofmeister, INFRARED-SPECTROSCOPY OF CAGEO3 PEROVSKITE TO 24-GPA AND THERMODYNAMIC IMPLICATIONS, Physics and chemistry of minerals, 21(1-2), 1994, pp. 78-84
Far-infrared absorbance spectra were collected from CaGeO3 with a meta
stable orthorhombic perovskite structure from 0 to 24.4 GPa. The absor
bance data are compatible with a reflectance spectrum which was collec
ted at ambient conditions from a polished, densely compacted polycryst
al. The reflectance spectrum shows 18 IR modes from 155 to 786 cm-1. A
detailed model for the density of states constructed from these new d
ata results in accurate calculation of heat capacity and new data on e
ntropy. Peak positions increase linearly with pressure. Mode Gruneisen
parameters (ranging from 0.72-1.56) decrease almost linearly with inc
reasing mode frequency which is consistent with deformations of the ox
ygen sublattice dominating the lattice vibrations. Neither discontinuo
us changes in the number of modes nor in these frequencies nor in band
widths are observed at pressures up to 24.4 GPa. Thus, conversion to
the tetragonal phase at approximately 12 GPa is not indicated.