M. A. Ryumin

Revised heat capacity and thermodynamic functions of GdVO4

The heat capacity of GdVO4 has been determined by adiabatic calorimetry in the range 5–345 K. The present experimental data and earlier results have been used to evaluate the thermodynamic functions of gadolinium orthovanadate (Cp0(T), S0(T), H0(T) − H0(0), and Φ0(T)) as functions of temperature (5–350 K). Its Gibbs energy of formation is determined to be ΔfG0(GdVO4, 298.15 K) = −1684.5 ± 1.6 kJ/mol.

Heat capacity and thermodynamic functions of xenotime YPO4(c) at 0–1600 K

The heat capacity of xenotime YPO4(c) was measured by adiabatic calorimetry at 4.78–348.07 K. Our experimental and literature data on H0(T)-H0(298.15 K) of Y orthophosphate were utilized to derive the Cp0(T) function of xenotime at 0–1600 K, which was then used to calculate the values of thermodynamic functions: entropy, enthalpy change, and reduced Gibbs energy. These functions assume the following values at 298.15 K: Cp0 (298.15 K) = 99.27 ± 0.02 J K−1 mol−1, S0(298.15 K) = 93.86 ± 0.08 J K−1 mol−1, H0(298.15 K) − H0(0) = 15.944 ± 0.005 kJ mol−1, Φ0(298.15 K) = 40.38 ± 0.08 J K−1 mol−1. The value of the free energy of formation ΔfG0(YPO4, 298.15 K) is −1867.9 ± 1.7 kJ mol−1.

The heat capacity and thermodynamic functions of EuPO4 over the temperature range 0-1600 K

The heat capacity of EuPO4 was measured by adiabatic calorimetry over the temperature range 9.81–298.48 K. The experimental and literature data were generalized to obtain the temperature dependence of the heat capacity of europium orthophosphate from 0 to 1600 K. This dependence was used to calculate thermodynamic functions (entropy, enthalpy, and reduced Gibbs energy). The data on the heat capacity of europium orthophosphate and diamagnetic lanthanum orthophosphate were used to estimate the noncooperative magnetic transition (Schottky anomaly) value.

Low-temperature heat capacity and thermodynamic functions of DyVO4

The heat capacity of dysprosium orthovanadate has been determined by adiabatic calorimetry in the range 6.12–343.26 K. The present and earlier data have been used to calculate the thermodynamic functions of DyVO4 in the temperature range 0–350 K. We have determined the absolute entropy and Gibbs energy of formation of dysprosium orthovanadate: S0(298.15 K) = 148.34 ± 0.11 J/(mol K), ΔfG0(298.15 K) = −1671.6 ± 2.1 kJ/mol. An anomaly has been detected at temperatures below 42 K, due to the Jahn-Teller phase transformation (TC = 14.42 K). We have determined the thermodynamic characteristics of the transformations in the temperature range 0–42.63 K.

Heat capacity and thermodynamic functions of YbPO4 from 0 to 1800 K

The thermodynamic functions of YbPO4 have been determined experimentally in the temperature range 6–1745 K. The results have been used to calculate temperature-dependent heat capacity, entropy, enthalpy increment, and reduced Gibbs energy of YbPO4 in the range 6–1800 K. The Gibbs energy of formation of ytterbium orthophosphate (ΔfG0(298.15 K)) has been determined.

Heat capacity and thermodynamic functions of LaVO4 and LuVO4 from 7 to 345 K

The heat capacities of lanthanum and lutetium orthovanadates have been measured at temperatures from 7 to 345 K using an adiabatic calorimeter. No anomalies have been detected in the heat capacity data. The thermodynamic functions (Cp0(T), S0(T), and H0(T) − H0(0)) of the two compounds have been calculated in the temperature range studied, and their Debye characteristic temperatures have been estimated.

High-temperature thermodynamic properties of LuPO4

The high-temperature enthalpy of lutetium orthophosphate has been determined as a function of temperature in the range 432.92–1744.58 K using drop calorimetry. The present and earlier experimental data have been used to calculate temperature-dependent heat capacity of LuPO4 in the range 1–1750 K.

Heat capacity and thermodynamic properties of GdPO4 in the temperature range 0–1600 K

The heat capacity of gadolinium orthophosphate (GdPO4) measured in the temperature range 11.15–344.11 K by adiabatic calorimetry and available literature data were used to calculate its thermodynamic functions at 0–1600 K. At 298.15 K, these functions are as follows: Cp0(298.15 K) = 101.85 ± 0.05 J K−1 mol−1, S0(298.15 K) = 123.82 ± 0.18 J K−1 mol−1, H0(298.15 K)–H0(0) = 17.250 ± 0.012 kJ mol−1, and Φ0(298.15 K) = 65.97 ± 0.18 J K−1 mol−1 The calculated Gibbs free energy of formation from the elements of GdPO4 is ΔfG0 (298.15 K) = −1844.3 ± 4.7 kJ mol−1.

Potassium Europium Molybdate Phosphate

The new compound K2Eu(MoO4)(PO4) has been synthesized. The compound is isostructural to the known potassium lanthanide molybdate phosphates (Ln = Nd, Sm, Dy, Yb, Lu). It crystallizes in space group Ibca (no. 73) with the unit cell parameters a = 19.734 Å b = 12.301 Å c = 6.978 Å V = 1693.8 Å, Rp = 2.19%, Rwp = 2.97%. K2Eu(MoO4)(PO4) decomposes above 1000°C and has a rather high luminescence intensity. The 5D0-7F2,4 electric dipole transitions are noticeably stronger than the 5D0-7F1,3 magnetic dipole transitions because of the noncentrosymmetric coordination environment of the europium ions in the complex molybdate phosphate.

Low-temperature heat capacity and thermal behavior of Zn0.98Co0.02O in the high-temperature region

The low-temperature heat capacity of Zn 0.98Co0.02O oxide was measured by adiabatic calorimetry. The formation of a solid solution was shown to be accompanied by a change in the entropy by 0.4 J/(K mol). No anomalies in the heat capacity or the thermal behavior confirming the phase transformations found earlier by other methods were observed. A heat capacity anomaly was revealed below 15 K and tentatively attributed to a change in the magnetic properties of the substance.