Features Of Vacancy Formation Energy Determination of 5-d Transition Metals Of The First Principles Taking Into Account The Temperature Factor

Abstract

This work is devoted to investigation of the behavior of the most common structural defect that determines the properties of the material – vacancies – at high temperatures. Theoretical study of the temperature dependence of the vacancy formation energy in pure 5-d fcc and bcc transition metals Au, Pt and W by means of density functional theory (DFT). The feature of this work is usage of experimental values of lattice parameters for the respective temperatures. The article discusses contributions to the vacancy formation energy, the results of computer simulation show that all of them can play an important role. It is shown, that thermal excitation has a significant impact on the vacancy formation energy at high temperatures. Also the possibility of compensation effect, i.e. the simultaneous change of free energy contributions to the vacancy formation energy in the 5-d fcc and bcc transition metals Au, Pt and W was confirmed. Contribution of the free energy vibrations and thermal electronic excitation depending on the temperature gives a good picture of the effect thermal expansion. Calculated vacancy formation energies are in good agreement with previous theoretical and experimental research. The effect of the compensation of different contributions to the vacancy formation energy can explain equality of vacancy formation energy values at different temperatures, observed in experimental studies, and justifies temperature dependence neglecting when modeling the properties of pure 5-d fcc and bcc transition metals.