一种超硬新材料BeP2N4的电子结构和力学性质及本征硬度

Electronic Structure,Mechanical Properties and Intrinsic Hardness of a New Superhard Material BeP_2N_4

基于密度泛函理论,采用局域密度近似(LDA)和广义梯度近似(GGA)泛函研究了硅铍石、尖晶石结构的BeP_2N_4材料的晶格参数、能带结构、态密度、分态密度、Mulliken布居值和弹性性质,计算结果与已有的实验值和理论值符合很好.能带结构和态密度表明两种结构的BeP_2N_4材料是宽的直接带隙的绝缘体材料.尖晶石结构BeP_2N_4的体弹性模量、剪切模量和弹性模量比硅铍石结构的相应的力学量大得多.利用Sung等提出的硬度经验划据和Gao等提出的基于Muilliken轨道重叠布居数的共价同体本征硬度计算方法,预测了两种结构的本征硬度值.计算结果表明硅铍石结构BeP_2N_4虽然体弹模量小,但是它并不是一种软的材料,而是一种易脆的硬度较硬的材料,随着压力增加硅铍石结构BeP_2N_4的脆性逐渐过渡到延性.尖晶石结构BeP_2N_4是一种易脆的超硬材料.采用GGA计算得到的硅铍石BeP_2N_4向尖晶石相转变压力为14 GPa,与理论预测值(24 GPa)相比偏小.

First-principles calculations were carried out to investigate the crystal structures, band structure, density of states, partial densities of states, Mulliken population and elastic properties of two BeP2N4 polymorphs namely phenakite and spinel. The generalized gradient approximation （GGA） and local density approximation （LDA） were used. The calculated results agree well with the experimental data and other theoretical calculations. The electronic structures of BeP2N4 indicate that they are insulators with wide bandgaps. The mechanical moduli of the spinel structure are larger than that of phenakite. The hardness of the two polymorphs was evaluated based on the methods proposed by Sung and Gao et al. Although the bulk modulus of phenakite is small the results indicate that it is a relatively hard material. On the other hand, the spinel structure is a super hard phase. When the pressure increases the phenakite structure gradually becomes malleable. The calculated GGA transition pressure from phenakite to spinel is 14 GPa, which is smaller than the predicted value of 24 GPa.