An equation for the heat capacity of solids

A new expression for the heat capacity of solids is proposed: a) for fitting the measured low-temperature heat capacity data on crystals, and b) for estimating heat capacity at high temperatures without violating the limit set by Petit and Dulong (1819). C_p = 3Rn(1 + k₁T⁻¹ + k₂T⁻² + k₃T⁻³) + (A + BT) + C'_p where R and n are the gas constant and the number of atoms in the chemical formulae, respectively. A and B are calculated from thermal expansion coefficient and isothermal bulk modulus data. The k_i's are determined by fitting the measured low-temperature heat capacity data. C'_p is the departures from the 3Rn limit for some substances due to cation disordering, anharmonicity and electronic contributions.The five constants in the proposed equation were determined for six minerals for which the physical properties have been well studied. The errors possibly resulting from experimental measurements or extrapolations of the thermal expansion coefficient and bulk modulus were carefully examined.