Thermodynamic Properties of Europium-Doped BaLa2WO7-Based Compounds

Abstract

Samples of compounds were synthesized by the solid-phase method from the systems of barium, lanthanum, europium, and tungsten ternary oxides with the general formula Ba(La,Eu)2WO7. The unit cell parameters were refined, and the content of additional phases was determined using the full-profile calculation of X-ray diffraction patterns. The heat capacities of these samples were studied by adiabatic calorimetry from the helium region to room temperatures (4.25–315 K), and the anomalies produced by the doping element were detected. Based on the experimental data, the lattice component of the heat capacity was recognized to determine the entropy and enthalpy changes in the anomalies, and the thermodynamic functions of the compounds were calculated within a range of 5–310 K. The standard thermodynamic functions are Cp,298.15 = 208.3 ± 0.7 J/(mol K), = 243.6 ± 1.5 J/(mol K), and H298.15 – H0 = 37360 ± 185 J/mol for Ba(La0.99Eu0.01)2WO7, Cp,298.15 = 208.7 ± 0.5 J/(mol K), = 244.0 ± 1.2 J/(mol K), and H298.15 – H0 = 37619 ± 142 J/mol for Ba(La0.97Eu0.03)2WO7, and Cp,298.15 = 208.8 ± 0.8 J/(mol K), = 242.6 ± 1.5 J/(mol K), and H298.15 – H0 = 37384 ± 190 J/mol for Ba(La0.95Eu0.05)2WO7.