Open AccessTheoretical calculations of stabilities and properties of transition metal borocarbides TM3B3C and TM4B3C2 compound
Author(s) -
胡前库,
侯一鸣,
吴庆华,
秦双红,
王李波,
周爱国
Publication year - 2019
Publication title -
wuli xuebao
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.199
H-Index - 47
ISSN - 1000-3290
DOI - 10.7498/aps.68.20190158
Subject(s) - crystallography , ternary operation , transition metal , materials science , chemistry , catalysis , biochemistry , computer science , programming language
To search new hard or superhard materials in transition-metal light-element compounds is a current research focus. Most of the past researches focused on binary phases such as transition metal borides, carbides and nitrides, while the researches on ternary phases were relatively rare. The single crystals Nb 3 B 3 C and Nb 4 B 3 C 2 were synthesized recently by using Al-Cu alloys as auxiliary metals and their structures were determined by Hillebrechtand Gebhardt. In the present paper, 29 TM 3 B 3 C and 29 TM 4 B 3 C 2 configurations are constructed by TM atoms ( TM = Sc to Zn, Y to Cd, Hf to Hg) replacing Nb atoms in the known Nb 3 B 3 C and Nb 4 B 3 C 2 configuration. By calculating the formation energy from first-principles density functional theories, only 13 TM 3 B 3 C and 11 TM 4 B 3 C 2 phases are stable compared with the three elemental substances of TM , boron and carbon. However compared with the most competing phases, only Ta 3 B 3 C, Nb 3 B 3 C and Nb 4 B 3 C 2 phases are stable thermodynamically. The metastable Ta 4 B 3 C 2 phase at 0 K becomes stable when temperature is higher than 250 K. Thus two new phases of Ta 3 B 3 C and Ta 4 B 3 C 2 are uncovered to be stable thermodynamically. Global structure searches conducted by the popular USPEX and CALYPSO softwares prove the Ta 3 B 3 C and Ta 4 B 3 C 2 phases to be the most favorable energetically. By calculating the phonon dispersion curves of the Ta 3 B 3 C and Ta 4 B 3 C 2 phase, no imaginary phonon frequencies are observed in the whole Brillouin zone, which demonstrates the dynamical stability of the Ta 3 B 3 C and Ta 4 B 3 C 2 phase. The calculated elastic constant of the Ta 3 B 3 C and Ta 4 B 3 C 2 phases satisfy the criteria of mechanical stability, showing that the Ta 3 B 3 C and Ta 4 B 3 C 2 phase are stable mechanically. The calculations of band structure and density of state show that the Ta 3 B 3 C and Ta 4 B 3 C 2 phases are both conducting, which mainly arises from the d electrons of Ta atoms. The calculated bulk modulus and shear modulus of the Ta 3 B 3 C and Ta 4 B 3 C 2 phases show their brittle nature. The hardness of Ta 3 B 3 C and Ta 4 B 3 C 2 phase are nearly the same and calculated to be about 26 GPa by Chen’s and Tian’s models, which illuminates that the two phases are hard but not superhard.