Abstract
High-pressure micro-Raman spectroscopic measurements of calcium ferrite-type MgAl2O4 and CaAl2O4 were made using a diamond-anvil cell high-pressure apparatus. The pressure dependence of frequencies of 18 Raman peaks for calcium ferrite-type MgAl2O4 and 26 Raman peaks for calcium ferrite-type CaAl2O4 were determined up to 20 GPa at ambient temperature. The mode Gruneisen parameter for each observed Raman mode was obtained from the pressure dependence of frequencies. Vibrational mode calculations by first principles using density functional theory were also performed for assignment of Raman peaks and for estimating frequencies of Raman inactive modes. From the obtained mode Gruneisen parameters and the results of the vibrational mode calculations, thermal Gruneisen parameters were determined to be 1.50(5) for calcium ferrite-type MgAl2O4 and 1.31(3) for calcium ferrite-type CaAl2O4. These thermal Gruneisen parameters were applied to heat capacity and vibrational entropy calculations using Kieffer model.
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