L. N. Komissarova

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.

On the synthesis and thermodynamic properties of SrLaGaO4-SrLaAlO4 solid solutions

Abstract Continuous solid solutions with a tetragonal structure of K 2 NiF 4 -type are formed in the SrLaGaO 4 -SrLaAlO 4 system. Samples of SrLaAl x Ga 1−x O 4 (0.0 ≤ x ≤ 1.0) were obtained by the freeze-drying method and their structural parameters and thermodynamic properties were studied by X-ray diffraction and heat flux Calvet calorimetry. Composition dependence of lattice constants was observed to follow Vegard’s low. Heats of solution of the SrLaAl x Ga 1−x O 4 samples in molten 2PbO·B 2 O 3 were measured, and enthalpies of formation and mixing were calculated. The possibility of eliminating the lattice mismatch of these phases and YBa 2 Cu 3 O x (x = 6.90–7.00) or Bi 2 Sr 2 CaCu 2 O 8 by proper selection of the Al/Ga ratio makes them perspective substrate materials for high-temperature superconducting thin films.

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.

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.

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.

Luminescence of Eu3+-Activated Potassium Scandium and Potassium Yttrium Phosphate Vanadates

The photoluminescence spectra of potassium rare-earth phosphate vanadates K3R1 – yEuy(PO4)x(VO4)2 – x(R = Sc, Y) were measured in the range 450–800 nm under excitation at 337 nm. The energies of the Stark components of the 7Fj(j= 0, 1, 2) multiplet were determined, and the crystal-field parameters were evaluated. The effects of the Eu3+concentration and PO43–/VO43–ratio on the luminescence of the materials studied and the concentration quenching of luminescence were analyzed. The materials with high Eu3+concentrations are shown to be potentially attractive as photo- and cathodoluminophors.

Luminescence Spectra of Eu3+-Activated Potassium Lanthanum and Potassium Gadolinium Phosphate Vanadates

The effects of the Eu3+concentration and PO4/VO4ratio on the photoluminescence (PL) of K3R1 – yEuy(PO4)x(VO4)2 – x(R = La, Gd) phosphate vanadates were studied over wide composition ranges. The energies of the Stark components of the 7Fj(j= 0, 1, 2) levels were determined, and the crystal-field parameters were evaluated. The concentration quenching of Eu3+luminescence was examined. The PL intensity was found to increase with Eu3+content up to y= 0.3. At higher Eu3+contents, the PL intensity decreases, without, however, complete luminescence quenching even at y= 1. K3Gd0.7Eu0.3(VO4)2and K3Gd0.7Eu0.3(PO4)0.3(VO4)1.7were found to exhibit the brightest photoluminescence.