Место издания:Université de Lorraine 2 Avenu de la forêt de Haye, BP 3 - 54501 Vandoevre Cedex, France
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Последняя страница:80
Аннотация:Abstract - The thermodynamic properties for sixteen compounds were optimized for the first time by means of a novel correlative method. It was found that maximum melting temperature and sum of atomic numbers Zi = (ZA+ZB ) of the isostructural phases were the important parameters in this thermodynamic approach. The enthalpies of formation (±0.4 kJ/ mol-at), Gibbs energies (±0.5-1.0 kJ/ mol-at), standard entropy (±0.5-1.0 J/ (K mol-at)), entropies of formation, and heat capacity (±0.2-0.4 (J / (K mol-at)) of compounds have been obtained. The literature available heat capacities values for phases, which have similar structure and do not take place solid-solid transitions, were analyzed with the assumption that these phases are similar at low and high temperatures for the same sums of atomic numbers. Thermodynamic properties of the unknown semiconductor TlN, as well as insufficiently known compounds BP, BAs and AlP have been evaluated. The proposed correlative method can be used to analyze the thermodynamic or physico-chemical properties of any isostructural phases in the systems AIII-BV, AII-BVI, RE-Me, and other ones.
The presented paper is a result of the fundamental thermodynamic study, which was started in the experimental and review papers [1]-[4]. The main idea of this contribution is based on the periodic law. The Russian scientist on calorimetry Kapustinsky established a linear relation between the enthalpy of formation and the logarithm of the total number of electrons (or the atomic numbers of the elements) for the first time. He called this relation as “the rule of thermochemical logarithmics” [5]. We developed this rule and established a rigid relation between the enthalpies of formation their melting temperatures and the sum of the atomic numbers of the elements for isostructural AIIIBV phases of sphalerite and wurtzite types [3], [4].
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, zinc blend type (ZnS), except the nitrides of aluminum, gallium, indium and thallium, which present a hexagonal cell, wurtzite type (ZnS). Boron nitride (hBN) is isostructural to graphite under normal conditions, and its high-pressure modification (cBN) is of blend type (ZnS) above 10 GPa.
The selection of the standard state of the elements AIII and BV groups is rather simple. Under standard conditions (T = 298K and P = 101325 Pa), all the elements are solid, except of nitrogen. In the standard state nitrogen is gas. But at some temperature and pressure it can be transformed into 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 [7]. It must be mentioned that nitrogen is in a solid state at such pressures and at room temperature. The transition from the solid crystallographic state to the liquid state takes place at T=308 K and P=2.8 GPa according to reference [8]. The white form phosphorus is selected as the standard state.
The relationship between reduced enthalpies ( ), standard entropies ( ) and reduced Gibbs energies of formation ( ) of the AIIIBV phases with the sum of their atomic numbers (Zi = ZA + ZB) was used to calculate the corresponding data of unknown phases. Method of similarity in the critical analysis of the heats capacities of phases is discussed and set of equations Cp(T) is presented.
References
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[2] V.P. Vassiliev, J.-C. Gachon, Thermodynamic properties of indium phosphide (InP). Inorg. Mater., 42 (2006) 1287-1292.
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