Heat capacity, entropy of Ln2(MoO4)3 (Ln = La, Sm, and Gd), and the high-temperature enthalpy of Ln2(MoO4)3 (Ln = Eu, Dy, and Ho)

Abstract

The low-temperature heat capacity of Ln₂(MoO₄)₃ (Ln = La, Sm, and Gd) is investigated by means of adiabatic calorimetry within the range of 60–300 K. The temperature dependences of the heat capacity are found and the values of the standard entropy are calculated, based on extrapolations to 0 K. Characteristic temperatures for molybdates are determined from the results of IR spectroscopic studies. The high-temperature enthalpy of Ln₂(MoO₄)₃ (Ln = Eu, Dy, and Ho) is measured via high-temperature microcalorimetry, and the temperature dependence of heat capacity is calculated in the range of 298–1000 K. Since samarium and gadolinium molybdates are of the same structural type as terbium molybdate, we can estimate the anomaly of the heat capacity in the low-temperature region using the data for terbium molybdate and find the entropy of samarium and gadolinium molybdates.