Density-functional-theory predictions of mechanical behaviour and thermal properties as well as experimental hardness of the Ga-bilayer Mo2Ga2C
Xinxin Qi, Weilong Yin, Sen Jin, Aiguo Zhou, Xiaodong He, Guangping Song, Yongting Zheng, Yuelei Bai
Abstract
Abstract Mo 2 Ga 2 C is a new MAX phase with a stacking Ga-bilayer as well as possible unusual properties. To understand this unique MAX phase structure and promote possible future applications, the structure, chemical bonding, and mechanical and thermodynamic properties of Mo 2 Ga 2 C were investigated by first-principles. Using the “bond stiffness” model, the strongest covalent bonding (1162 GPa) was formed between Mo and C atoms in Mo 2 Ga 2 C, while the weakest Ga-Ga (389 GPa) bonding was formed between two Ga-atomic layers, different from other typical MAX phases. The ratio of the bond stiffness of the weakest bond to the strongest bond (0.33) was lower than 1/2, indicating the high damage tolerance and fracture toughness of Mo 2 Ga 2 C, which was confirmed by indentation without any cracks. The high-temperature heat capacity and thermal expansion of Mo 2 Ga 2 C were calculated in the framework of quasi-harmonic approximation from 0 to 1300 K. Because of the metal-like electronic structure, the electronic excitation contribution became more significant with increasing temperature above 300 K.