Open AccessFirst-principles calculations of stabilities and physical properties of ternary niobium borocarbides and tantalum borocarbides
Author(s) -
Qicheng Hu,
Shuang-Hong Qin,
Qinghua Wu,
Dandan Li,
Bin Zhang,
Wei Yuan,
Li-Bo Wang,
Aiguo Zhou
Publication year - 2020
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.69.20200234
Subject(s) - ternary operation , crystallography , octahedron , tantalum , materials science , niobium , tantalum nitride , chemistry , crystal structure , metallurgy , computer science , programming language
Transition-metal light-element compounds are potential candidates for hard materials. In the past, most of studies focused on the binary transition metal borides, carbides and nitrides, while the researches of ternary phases are relatively rare. In this paper, the structure units of the known Nb 3 B 3 C and Nb 4 B 3 C 2 phases are first analyzed to be Nb 6 C octahedron and Nb 6 B triangular prism, respectively. By stacking the Nb 6 C octahedron and Nb 6 B triangular prism, twenty ternary Nb-B-C and twenty ternary Ta-B-C configurations with different compositions are constructed. The chemical formula of these Nb-B-C and Ta-B-C configurations can be defined to be Nb ( m + n + 2) B (2 m + 2) C n and Ta ( m + n + 2) B (2 m + 2) C n , respectively. Using first-principles density functional calculations, thermodynamical, dynamical and mechanical stabilities of the constructed ternary Nb-B-C and Ta-B-C configurations are investigated through calculating their enthalpies of formation, phonon dispersions and elastic constants. Five Nb-B-C (Nb 3 B 3 C, Nb 4 B 3 C 2 , Nb 6 B 4 C 3 , Nb 7 B 4 C 4 and Nb 7 B 6 C 3 ) phases and six Ta-B-C (Ta 3 B 3 C, Ta 4 B 3 C 2 , Ta 6 B 4 C 3 , Ta 7 B 4 C 4 , Ta 7 B 6 C 3 and Ta 3 BC 2 ) phases are predicted to be stable by analyzing the constructed ternary Nb-B-C and Ta-B-C phase diagrams, in which the seven phases (Nb 6 B 4 C 3 , Ta 3 B 3 C, Ta 4 B 3 C 2 , Ta 6 B 4 C 3 , Ta 7 B 4 C 4 , Ta 7 B 6 C 3 and Ta 3 BC 2 ) are first predicted to be stable. The Nb 6 B 4 C 3 , Ta 6 B 4 C 3 , Ta 4 B 3 C 2 and Ta 3 B 3 C phases are stable when temperature is higher than 1730, 210, 360 and 1100 K, respectively. And the Ta 3 BC 2 phase is stable only when temperature is lower than 130 K. The calculated results about mechanical and electric properties show that these Nb-B-C and Ta-B-C phases are conductive materials with a high hardness in a range of 23.8–27.4 GPa.