Vibrational entropy of disordering in omphacite.

Authors :: Benisek A
Dachs E
Carpenter MA
Joachim-Mrosko B
Vielreicher NM
Wildner M
Source :: Physics and chemistry of minerals [Phys Chem Miner] 2023; Vol. 50 (4), pp. 36. Date of Electronic Publication: 2023 Nov 27.
Publication Year :: 2023
Abstract: The cations of an ordered omphacite from the Tauern window were gradually disordered in piston cylinder experiments at temperatures between 850 and 1150 °C. The samples were examined by X-ray powder diffraction and then investigated using low-temperature calorimetry and IR spectroscopy. The low-temperature heat capacity data were used to obtain the vibrational entropies, and the line broadening of the IR spectra served as a tool to investigate the disordering enthalpy. These data were then used to calculate the configurational entropy as a function of temperature. The vibrational entropy does not change during the cation ordering phase transition from space group C2/c to P2/n at 865 °C but increases with a further temperature increase due to the reduction of short-range order.<br />Supplementary Information: The online version contains supplementary material available at 10.1007/s00269-023-01260-7.<br />Competing Interests: Conflict of interestThe authors declare no competing interests.<br /> (© The Author(s) 2023.)