SYNTHESIS, RADIOGRAPHY AND THERMODYNAMICS CUPRATE-VANADATO-MANGANITE LaLi₂CuVMnO_7.5

The article presents the results of synthesis, radiographic and thermodynamic studies of the cupratevanadato-manganite compound LaLi₂CuVMnO_7.5. Using ceramic technology, a new cuprate-vanadatomanganite LaLi₂CuVMnO_7.5 was synthesized. The structure was analyzed by X-ray diffraction (XRD). The Xray images were indicated by the analytical method. Pycnometric densities were determined in glass pycnometers with a volume of 1 ml. 3 times and the data were averaged. The results show that LaLi₂CuVMnO_7.5 crystallizes in cubic syngony with lattice parameters: а=14,01 ± 0,01 Å; Z=4; Vo=2747,18 ± 0,03 Å^³; V_oun._cell.=686,87 ± 0,87 ų, ρ_x-ray.=4,27 and ρ_picn.=4,26 ± 0,005 g/sm³. The temperature dependence of the heat capacity of LaLi₂CuVMnO_7.5 was studied using a serial IT-C-400 calorimeter in the range of 298.15-673 K. The calibration of the device was carried out based on determining the thermal conductivity of the heat meter. For this purpose, experiments were conducted using a copper sample and an empty ampoule. At each temperature (in increments of 25 K), five parallel experiments were performed, and the results were processed using methods of mathematical statistics by calculating the mean value. The performance of the device was verified by determining the heat capacity of α-Al₂O₃. Based on experimental data, equations describing the temperature dependence were derived. It was established that LaLi₂CuVMnO_7.5 undergoes a λ-shaped effect at 348 K, which is likely related to a second-order phase transition. Using a calculation method, the values of the thermodynamic functions H°(T)-H°(298,15), S°(T), Ф**(Т) for the studied cuprate-vanadate-manganite were evaluated. The research results are important for further studies of the electrophysical properties of this compound and are also of interest for predicting valuable physicochemical properties and the certification of the laboratory prototype of LaLi₂CuVMnO_7.5.

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