Discovery of new MAX-phase-like layered ternary carbide V8P6C: Crystal structure, thermal expansion, and elastic properties

Due to the laminated structure, MAX phases and MAX-phase-like compounds possess outstanding dam -age tolerance capability with good thermal/electrical conductivity and other charming functional prop-erties, showing a bright future for structural-functional uses. Here, a new MAX-phase-like ternary car -bide V8P6C with layered characteristics was discovered. Contrary to the alternate stacking of hexagonal-arranged M/A/X atom layers in MAX phases, V8P6C has a layered structure formed by a repeated stacking of the slabs consisting of V6C-octahedrons and VP6-distorted-octahedrons in three-atomic layers thick. The thermal expansion anisotropy was revealed, with the thermal expansion coefficients (TECs) along a-axis, c-axis, and the average value, equal to alpha a= 8.55(5) mu K -1, alpha c= 10.23(5) mu K -1, and alpha L= 9.14(5) mu K -1, respectively. The dilation along the c-axis was mainly dominated by out-plane V-P bonds be-tween layered slabs. According to the pressure-dependent lattice parameters, the polycrystalline bulk modulus ( B 0 = 185(9) GPa) and high compressibility anisotropy factor (Ba/Bc = 1.64) was found. Mean-while, the second-order elastic constants were calculated, and the elastic moduli, E = 303 GPa, B = 198 GPa, G = 122 GPa, and nu = 0.246, were obtained. And the weak connection between layer slabs by out-plane V1-P bond was revealed by the bond stiffness model, with a bond stiffness close to the M-A bond in MAX phases. Furthermore, good damage tolerance capability was predicted according to Paugh's ratio (G/B= 0.616) and Cauchy pressure (Pa = 0 GPa, Pc =-7.5 GPa), even better than those of typical MAX phases. The discovery of V8P6C provides a new member of MAX-phase-like damage-tolerant ceramic with relatively low density, moderate thermal expansion, and anisotropic compressibility, and the unique layered structure is inspiring for exploring new layered ternary ceramics.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

Due to their laminated structure, MAX phases and MAX-phase-like compounds possess excellent damage tolerance capability, thermal/electrical conductivity, and other functional properties, showing promising prospects for structural-functional applications. In this study, a new MAX-phase-like ternary carbide, V8P6C, with layered characteristics was discovered. It has a layered structure formed by repeated stacking of V6C-octahedrons and VP6-distorted-octahedrons, exhibiting thermal expansion anisotropy and high compressibility anisotropy. The unique structure and properties of V8P6C were revealed through experiments and calculations, and its good damage tolerance capability was predicted.