基于第一性原理的Mo_(2)CoB_(2)三元过渡金属硼化物掺杂效应研究

Doping Effects of Mo_(2)CoB_(2)Ternary Transition Metal Boride:a First-Principles Study

利用第一性原理计算研究了掺杂第四周期过渡金属元素对Mo_(2)CoB_(2)的结构、力学和热力学性质的影响。通过计算结合能和形成焓以及与Born-Huang标准比较,发现所有模型都满足力学与热力学稳定条件。采用点缺陷理论确定了掺杂元素在Mo_(2)CoB_(2)晶体中的占位以及占位偏好。结果表明,Sc和Ti对Mo点位表现出强烈的占位偏好,V对Mo点位仅有较弱的占位偏好。同时,Cr、Mn、Fe、Cu和Zn对Co点位具有较弱的占位偏好,而Ni对Co点位有较强的占位偏好。通过对比计算得到德拜温度,发现除Mo7TiCo4B8、Mo7VCo4B8和Mo7CrCo4B8外,其他掺杂模型的德拜温度都低于未掺杂模型,这说明实验中应尽量避免在Mo_(2)CoB_(2)硬质相中大量添加除Ti、V和Cr以外的过渡金属元素。最后,除Cr掺杂模型外,其他掺杂模型的硬度计算结果都低于未掺杂的模型。同时,占据偏好点位的掺杂元素模型的硬度通常比占据非偏好点位的更高。本研究为开发性能更好的Mo_(2)CoB_(2)金属陶瓷提供了理论支持。

The first-principles calculation was used to investigate the influence of doping fourth-period transition metal elements on the structural,mechanical,and thermal properties of Mo_(2)CoB_(2).Through the calculation of cohesive energy and formation enthalpy as well as the calculation comparison between the obtained results and Born-Huang criterion,all doped compounds are thermodynamically and mechanically stable.Point defect theory was employed to determine the occupation sites and occupation preference of doped elements in the Mo_(2)CoB_(2)crystal cell.Results show that Sc and Ti exhibit strong preference for Mo sites,and V has a weak preference for Mo sites.Additionally,Cr,Mn,Fe,Cu,and Zn have a weak preference for Co sites,and Ni has a strong preference for Co sites.Debye temperatures were obtained by the contrast calculation.The results reveal that except Mo7TiCo4B8,Mo7VCo4B8,and Mo7CrCo4B8,the doped models all have lower Debye temperatures than the undoped model,suggesting that except Ti,V,and Cr elements,the addition of transition metal elements of large quantity into the Mo_(2)CoB_(2)hard phase should be avoided.Furthermore,except that of the Cr-doped model,the hardness of the doped models is lower than that of the undoped model,and the models with doped elements at preferential sites normally exhibit higher hardness than those at non-preferred sites do.This research provides theoretical basis for the development of Mo_(2)CoB_(2)-Co cermet with improved properties.