A first-principles prediction of electronic, mechanical and thermodynamic properties of α-LuAlB4 and β-LuAlB4 ceramics

In this work, the electronic, mechanical and thermodynamic properties of two polymorphs of LuAlB4 ceramics (alpha-LuAlB4 and beta-LuAlB4) were predicted through first-principles calculations. The formation enthalpy of alpha-LuAlB4 and beta-LuAlB4 is -1.433 kJ/mol and -1.429 kJ/mol, respectively, indicating that LuAlB4 ceramics are stable. Crystal structure and electronic structure analysis revealed that strong B-B bonds greatly contributes to the high hardness of LuAlB4 ceramics. The analysis of state density showed that LuAlB4 is a layered ternary boride with metallic properties. Elastic anisotropy indexes, 3D surface constructions and 2D projections of elastic modulus showed that the elastic anisotropy of alpha-LuAlB4 is higher than beta-LuAlB4. In addition, the phonon dispersion curves verified the thermodynamic stability of LuAlB4 ceramics. Finally, according to elastic constants and modulus, the Debye temperature, directional sound velocities and thermal conductivities of LuAlB4 ceramics were discussed.