Internal energy and parameters of the order-disorder phase transition in titanium monoxide TiO y

Abstract

Abstract-Quantum mechanical ab initio calculations are used to simulate the free energy functions for tita nium monoxide TiO y . The effect of the long range order of the Ti 5 O 5 type superstructure on the internal energy of the compound is studied by the supercell method. The dependences of the configuration entropy and free energy on the long range order parameter are determined. It is found that the order-disorder phase transition in titanium monoxide must occur in accordance with the mechanism of the first order phase tran sition with a critical value of the long range order parameter of 0.971. The calculated parameters of the phase transition are compared with the experimental data and the results obtained using the model of point charges and by calculating the Madelung energy. It is concluded that the short range order and the phonon entropy must be taken into account in calculating the equilibrium phase diagrams for strongly nonstoichiometric compounds.

Effect of high pressures and high temperatures on the structure of nanostructured titanium monoxide

“…Oxides, carbides and nitrides of transition metals of IV -V groups of the periodic table having B1 type crystal structure feature wide homogeneity regions due to an anomalously high concentration of structural vacanciescrystal lattice sites which are not occupied by atoms [1,2]. Vacancies are associated not only with nonstoichiometry, but also with short-and long-range order effects allowing a great number of various phases and structural modifications of a compound to be obtained while retaining the type of its basis crystal structure [3][4][5][6][7][8]. This peculiarity is of importance in terms of the topical problem of designing materials with pre-defined properties.…”