| Superhard material refers to the one whose Vickers hardness is more than 40 GPa. With the rapid development of social industry, superhard materials in today’s society have the irreplaceable effects on the basic scientific research and application area. High hardness material can be used for cutting, grinding, polishing and coating process, also can be widely used in oil drilling,metallurgy,construction, instrumentation and aerospace and other cutting-edge science. diamond is the material which has the highest hardness in nature, but its natural reserves is limited and hard to meet industrial demand.Therefore, a considerable number of experimental and theoretical workers are committed to new superhard materials’ research.The hardness of cubic boron nitride(c-BN) and BC5 are second only to diamond, But the synthetic cost is higher. Recent years,researchers found some transition-metal borides(TMBs) with high bulk modulus and shear modulus can be compounded under relatively low cost,these substances are potential superhard materials.the research on TMBs is favored by more and more researchers.Thus, several kinds of boride iridium structures have been theoretically studied in this article.This paper uses MS software’s CASTEP module that is based on the plane wave pseudopotential density functional theory to calculate. Calculated with Vanderbilt pseudopotential, the exchange and correlation function is described by local density approximation(LDA) and generalized gradient approximation(GGA).we obtain stable structure and equilibrium lattice parameters by establishing and optimizing the model.We calculate elastic constants、bulk modulus、shear modulus and electronic structure of P1- Ir B and P5- Ir B2, Ni As- Ir B, anti- Ni As- Ir B, Na Cl- Ir B, WC- Ir B, Cs Cl-Ir B,Re B2 Under the zero pressure by GGA,LDA approximate method is separately used. Further calculating each structures’ elastic constants 、 bulk modulus 、 shear modulus and equilibrium lattice parameters within the scope of 0-100 GPa,we found that with the pressure increasing, the elastic constants and bulk modulus、shear modulus of several kind of structures,including:P1-Ir B,Na Cl-Ir B,Ni As-Ir B,anti-Ni As-Ir B, Cs Cl-Ir B,incompressibility gradually enhanced.WC-Ir B and Re B2-Ir B2 both belong to the hexagonal system, according to the hexagonal system stability conditions, when the pressure comes to 10 GPa,WC-Ir B structure mechanics stability is destroyed, so appear C11, G, E changes. Similarly, when the pressure is 80 GPa and the elastic constants of Re B2-Ir B2 also does not meet the above conditions, this can also explain that when C11 and G, E are under this kind of pressure condition, the crystal structure and mechanical properties are no longer stable.For P5-Ir B2 structure, with the increase of the pressure, incompressibility increases gradually, but when the pressure increases to 50 GPa, Young’s modulus and the lattice constant in the direction of b changes exceptionally, the analysis shows that under the condition of the pressure,crystal stability conditions are no longer satisfied. It suggests that the crystal structure is changed under high pressure.In addition, the analysis of band structure and density states figure for P1-Ir B,P5-Ir B2,Na Cl-Ir B,Ni As-Ir B, anti-Ni As-Ir B, WC-Ir B,Cs Cl-Ir Band Re B2-Ir B2 indicate that eight kinds of structure have metal properties.Finally, in this paper, the calculated results of P1–Ir B,P5-Ir B2,Na Cl-Ir B,Ni As-Ir B,Cs Cl-Ir B, anti-Ni As-Ir B,WC–Ir B and Re B2-Ir B2 show that the eight kinds of structure of elastic modulus value and shear modulus value are large,covalent effect between B and Ir atoms is strong. They are potential compression material. The paper’s research results can provide certain theoretical guidance for these new experimental exploration synthetic hardness materials. |
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