First-principles Study Of The Structural Stability And Elastic Properties Of TMB₄（TM=V, Cr, Mn, W）

In recent years, for the transition metal tetraborides has good elastic properties, thus arouse people to research on it extensivly from theory and experiment. In this paper, the potential superhard material——transition metal tetraboride TMB4(TM=V, Cr, Mn, W) have been studied by using the first principle based on the density functional theory within the GGA and LDA method as the exchange of correlation functions, and further study the structure stability and elastic properties of it under high pressure. In view of the fact that the superhard materials has wide application in industry, and hope that through study on TMB4 can be provide some foundation and guides for the predicte of new potential superhard materials in the future.This paper is divided into five chapters to discuss material TMB4(TM=V, Cr, Mn, W), the first chapter introduces the research background and significance of this paper, the second and third chapters introduces the relevant theoretical knowledge of first principles density functional theory and hardness, the fourth chapter introduces the structure and elastic properties TMB4(TM=V, Cr, Mn) and a variety of structures(includes Immm, Pnnm, Pmmn, C2/m and P63/mmc structures) for WB4 on the stability and elastic properties, the fifth chapter is the conclusion of this paper. The innovations of this paper are as follows:(1) Studied the structure stability and elastic properties of TMB4(TM=V, Cr, Mn, W) under extreme high pressure.(2) According to the analysis of elastic constants for the mechanical stability criteria, the TMB4(TM=V, Cr, Mn), and the Immm, Pnnm, Pmmn, C2/m structure of WB4 are all keep the mechanical stability at ground state and high pressure.(3) The TMB4(TM=V, Cr, Mn) has very strong dependence on pressure, the Immm structure of the Cr B4 is the most difficult to compression under ground state.(4) For the WB4, the C2/m structure of the WB4 has superior mechanical property(hardest and incompressible) among the Immm, Pnnm, Pmmn and C2/m structures. At the same time, confirmed that the P63/mmc structure of WB4 is not stable.(5) For the B/G ratio, the Cr B4, VB4 and C2/m structure of Mn B4 shows brittle nature within 100 GPa for the B/G ratio lower than 1.75. And the Pnnm structure of MnB4 is prone to ductility when the pressure above 73 GPa.