Crystal structures and mechanical properties of tungsten monocarbide predicted by first-principles investigations

• Published in: Journal of applied physics 2021-11, Vol.130 (19)
• Main Authors: Zhang, Huai-Yong, Guo, Yun-Dong, Min, Shuo, Ma, Chang-You, Li, Jian
• Format: Article
• Language: English
• Subjects: Applied physics; Approximation; Bulk modulus; Compressibility; Crystal structure; Dynamic stability; First principles; Hard materials; Hardness; Mathematical analysis; Mechanical properties; Transition pressure; Tungsten carbide
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/5.0067140

The crystal structure of tungsten monocarbide (WC) is researched from 0 to 650 GPa through first principles calculations. The results verify that the experimental structure (hP2-WC) with the space group P 6 ¯m2 is the most stable phase in a wide range of pressure. Above 231 GPa, a new stable structure (space group P63/mmc, hP4-WC) is found to be the most stable phase, and it will transform to a CsCl-type phase (cF8-WC) around 582 GPa. Phonon calculations reveal that the hP4-WC phase is dynamically stable and may be a metastable structure at ambient conditions. The cF8-WC phase possesses dynamical stability above 20 GPa. The hP4-WC phase is a low compressible material with a large bulk modulus of 377 GPa at zero pressure. The hardness values of hP2-WC and hP4-WC at zero pressure are 32 and 21 GPa, respectively, while the cF8-WC phase possesses a hardness of 21 GPa at 20 GPa, implying that these phases are potential hard materials. The temperature–pressure phase boundary of WC is obtained by means of the quasi-harmonic approximation method. As the temperature increases, the transition pressure from hP2-WC to hP4-WC remained nearly unchanged. The transition pressure between hP4-WC and cF8-WC decreases with the increasing temperature.