ИСТИНА

DOI: https://doi.org/10.1051/matecconf/20130301078 The present paper is the result of the fundamental thermodynamic study, which started with the experimental and review papers. The main idea is based on the periodic law. The Russian scientist Kapustinsky established by calorimetry a linear relation between the enthalpies of formation and the logarithm of the total electrons’ number of the compounds for the first time. He called this relation “the rule of thermochemical logarithmics”. We developed this rule and established a strict relation between the enthalpies of formation, the melting temperatures and the sum of A and B atomic numbers for isostructural AIIIBV phases of sphalerite and wurtzite types. We applied our model to develop the thermodynamic calculation of the properties for isostructural compounds. Every binary system AIII-BV, apart from B-As system, has only one compound AIIIBV with a congruent melting point. Most of the known AIIIBV compounds crystallize in a cubic system, of the ZnS type, except the nitrides of aluminum, gallium, indium and thallium, which have a hexagonal cell, ZnS wurtzite type. Boron nitride (hBN) is isostructural to graphite under normal conditions, and its high-pressure modification (cBN) is of blend ZnS type above 10 GPa. The selection of AIII and BV standard state is rather simple. Under standard conditions (P = 101325 Pa) at T = 298 K, all these elements are solid, but nitrogen which is a gas, while at some temperatures and pressures it may be solid. The experimental study of nitride systems is extremely complicated due to the fact that nitrogen gas is formed before its fusion. The liquidus curve depends on nitrogen pressure. It is necessary to maintain a nitrogen pressure between 6 and 10 GPa for nitrides [7]. It must be mentioned that nitrogen is solid at such pressures and at room temperature. The transition from solid to liquid takes place at T = 308 K and P = 2.8 GPa according to reference [8]. In view of the fact that phosphorus has ten forms allotropic forms we selected the white phosphorus as standard state. According to obtained results the white form is more suitable for our correlation model. The relationship between the reduced enthalpies, standard entropies and reduced Gibbs energies of formation of AIIIBV phases and the sum of their atomic numbers (Zi = ZA + ZB) was used to calculate the corresponding data of unknown phases. The method of similarity in the critical analysis AIIIBV heats capacities is discussed and a set of equations Cp(T) is presented.