Theoretical And Applied Study On The Thermodynamic Properties Of MoSi₂

In recent decades,ternary layered compounds MoSi₂ attract extensive attention for their perfect properties.For example,both metallic and ceramic property,high melting point,high hardness,fine conductivity and thermal conduction,chemical stability and so on.They are excellent refractory ceramics material with chemical inertness for molten metal.It has demonstrated the formidable vitality under the environment of high temperature.Especially it plays an unique role in many fields which metal and ceramics can not play.Despite the technological developments of MoSi₂,some behaviors of MoSi₂ under the high temperature have not been paid enough attention.Through the calculation of thermodynamic properties of MoSi₂ materials,can accurately reveal the mechanism of its performance under high temperature,provide a theoretical basis for further improving the performance and application of MoSi₂ material In this paper,we employed first-principle method CASTEP（Cambridge Sequential Total Energy Package）code of Materials studios based on DFT（density functional theory）to obtain phonon spectrum of MoSi₂,systematically investigated the thermodynamic properties of MoSi₂,obtained heat capacity at constant volume,heat capacity at constant pressure,thermal expansion coefficient,Debye temperature,bulk modulus,standard molar Gibbs free energy of formation,standard molar enthalpy of formation,standard entropy et al.thermal data as functions of temperature.The calculation results show that the absolute value of the cohesive energy of the MoSi₂ structure C11 b is larger than that of the C40 structure,which means that the MoSi₂ stability of the C40 structure is not as good as that of the C11 b structure.In other thermodynamic properties,the structure of the two kinds of MoSi₂ remained the same characteristics:The thermal expansion coefficient sharply increases with temperature,then slowly.The bulk modulus of MoSi₂ approach to the constant at low temperature,then decrease linearly.The standard entropy of MoSi₂ increase with temperature,which is due to microcosmic states increase.Because the more molecular weight,the more entropy.Simultaneously the standard molar Gibbs energy of formation and standard molar enthalpy of formation show inverse condition.At low temperature（0-30K）,the heat capacity is close to 0.The heat capacity follows the Debye T3 law,at the high temperature,heat capacity follow the anharmonic effect.With the increase of temperature,increases rapidly.At about 750 K gradually approaches a constant,namely the Dulong Petit limit（Dulong-Petit）.By using the first principles simulation speculated that the thermodynamic properties of MoSi₂ and experimental values demonstrates the accuracy of the calculation,can provide theoretical basis for engineering of MoSi₂ under high temperature and high pressure use,and also to improve the properties of materials,expand the application ranges of the foundation.