The low-temperature heat capacity and standard entropy of synthetic huttonite ThSiO4

The low-temperature heat capacity of synthetic huttonite ThSiO4 has been measured from T = (2 to 300) K. The sample was synthesised successfully from SiO2 and ThO2 by solid-state reaction at T = 1873 K at atmospheric pressure. From the calorimetric results, the value for the standard entropy Sm∘ (ThSiO4, huttonite, 298.15 K) = (104.3 ± 2.0) J · K−1 · mol−1 has been obtained. This value indicates that the entropy of reaction from SiO2 and ThO2 is negative, giving a positive entropy term (−T · ΔrS) of the Gibbs free energy of reaction. The implications of this finding are discussed extensively.