Thermophysical properties of Ca₂GeO₄ over the temperature range between (6 and 350) K

Highlights: • The temperature dependence of isobaric heat capacity of Ca₂GeO₄ has been measured. • The experimental data were used to calculate standard thermodynamic functions. • The low-temperature X-ray diffraction was used for determination thermal expansion coefficient. • The experimental data were used to calculate isochoric heat capacity of the clear Ca₂GeO₄. • A simple model of the isochoric heat capacity Debye and Einstein was used for calculate S_v,m. - Abstract: The isobaric heat capacity of monocrystalline Ca₂GeO₄ (olivine structure) has been measured between T = (6 and 350) K by precision adiabatic vacuum calorimetry for the first time. The experimental results have been used to calculate the standard (r^o = 0.1 MPa) thermodynamic functions C_p,m^o/R, Δ₆^TH_m^o/RT, Δ₆^TS_m^o/R and Φ_m^o/R = Δ₆^TS_m^o/R − Δ₆^TH_m^o/RT (where R is the universal gas constant) of Ca₂GeO₄ (cr) over the range from T = (6 to 350) K. The thermal expansion coefficient (α) of this synthetic mineral has been determined from low-temperature X-ray measurements over the range from T = (100 to 300) K. Isochoric heat capacity S_v,m/R has been calculated using this low-temperature X-ray measurements and available compressibility data. The «acoustical» and «optical» components of the isochoric heat capacity have been estimated. The «optical» component of the one are calculated from the vibrational frequencies (ν) as measured by Raman spectroscopy with different polarization at room temperature and at 1 bar