ИСТИНА

Critical Analysis of the Heat Capacities of Diamond and Graphite Valery P. Vassiliev Lomonosov Moscow State University, Russia; valeryvassiliev@yahoo.fr; Abstract The investigation of the heat capacities of systems based on light elements such as lithium, beryllium, boron, and carbon is an extremely complex experimental task. The presence of impurities or variations in the isotopic composition has a stronger effect on the physicochemical properties than on the heavy elements. In accordance with our proposed concept of similarity put forward by us, isostructural substances with the same sum of atomic numbers have the same heat capacities per J·(mole-atom)-1·K-1 [1, 2]. Diamond and cubic boron nitride have the same crystal structure of the type (Fd¯3 m). Both substances are in a metastable state under normal conditions. Synthetic diamond and various modifications of boron nitrides contain various impurities due to the specifics of their synthesis. Consequently, cubic boron nitride must have the same heat capacity as the diamond. Similarly, we can compare the isostructural phases of graphite and BN with a hexagonal structure. All deviations from this rule are caused by the presence of impurities in the final product. The functions Cp and Cv using both the Debye models and the Maier-Kelley equation are proposed to describe the heat capacity of substance in solid state using the in-house software on the base of commercial one DELPHI-7. They make it possible to calculate the heat capacity values equal to the experimental data within the range of the deviation. References: [1] V.P. Vassiliev, W. Gong, A.F. Taldrik, S.A. Kulinich. Method of the correlative optimization of heat capacities of isostructural compounds. J. Alloys Comp. 552 (2013) 248–254. https://doi.org/10.1051/matecconf/20130301074 [2] V. P. Vassiliev, A. F.Taldrik. Description of the heat capacity of solid phases by a multiparameter family of functions. J. Alloys Comp. 872 (2021) 159682. https://doi.org/10.1016/j.jallcom.2021.159682