YPd_3X(X=B,C)晶体结构、弹性性质与电子结构的第一性原理研究

First-principles study on the crystal structures,elastic modulus and electronic structures of YPd_3X(X=B,C)

在广义梯度近似(GGA)和GGA+U(在位库仑势)下,采用第一性原理方法系统地研究了三元过渡金属硼碳化合物YPd3X(X=B,C)的晶体结构、弹性性质、电子结构和成键特性.计算的晶格参数和体弹性模量均与报道的实验结果吻合,而YPd3X(X=B,C)的弹性参数计算值则表明YPd3C的硬度大于YPd3B.根据晶体机械稳定标准得到YPd3B和YPd3C的失稳临界压强分别约为16.5GPa和23GPa.由Pugh经验关系可知YPd3X(X=B,C)均属于韧性材料,且YPd3B的韧性略高于YPd3C.电子能带结构分析表明YPd3B和YPd3C均具有金属特性,且导电能力相当.由态密度和电荷密度分析得知,X与Pd之间形成较强的共价键,而Y与Pd3X之间形成离子键,化学键键能的不同是两种材料的弹性参数存在差异的内在原因.上述的研究结果为YPd3X(X=B,C)的力电材料的设计和应用提供了一定的理论依据.

The crystal structures, elastic parameters, electronic structures and bonding characteristics of the ternary borides or carbides of transition metals YPd3 X（X=B, C） have been investigated by first- principles method within the generalized gradient approximation （GGA） and GGA＋U. The calculated lattice parameters and bulk modulus are in good agreement with the reported experimental data. The calculated elastic parameters of YPd3X（X=B, C） indicate that the hardness of YPd3B is larger than YPd3C. Meanwhile, the calculated instability thresholds of pressure of YPd3B and YPd3C are, respec- tively, close to 16.5GPa and 23GPa according to the standard of crystal mechanically stability. Based on Pugh empirical relationship, it can be found that the compounds of YPd3X（X=B, C） are of ductile ma- terials and YPd3 B is little more ductile than YPd3 C. The analyses of the band structure tell us that YPd3 B and YPd3C both have metal properties and their abilities of conduct electricity are almost equal to eachother. At last, the analyses of the density of states and Milliken charge distribution show that the cova- lent bond is formed between X and Pd and the ionic bond is formed between Y and Pds X while the ener- gy difference of chemical bond is the underlying reason for the elastic parameters having diversity of YPdsX（X=B, C）. In a word, the involved results of the study provide a theoretical basis for the design and application of electromechanical materials YPd3X（X=B, C）.