First-principles study of bonding,elasticity-relevant and acoustic properties of BaAlBO3F2

The band structure, density of states, charge densities, and elasticity-relevant properties of BaAlBO₃F₂ are obtained by first-principles density functional calculations within the generalized gradient approximation. Other elasticity-relevant constants, such as the the Young's modulus, Poisson ratio, velocity of acoustic waves, and the Debye temperature are also deduced from the elastic constants. Bonding analysis demonstrates that BaAlBO₃F₂ has different bonding properties between basal (ab) plane and c axis. The analyses on elasticity-relevant properties indicate BaAlBO₃F₂ is mechanically stable and anisotropic. It is also shown that BABF is an ionic crystal with brittle character. Our these results give a reasonable explanation for the experimental finding that BaAlBO₃F₂ is apt to crack along c axis. Proceeding from Christoffel equation, we discuss the propagation properties of acoustic modes in BaAlBO₃F₂ to give a theoretical guidance for measuring its elastic constants. Research shows that the calculated average velocities of longitudinal and transverse modes from Christoffel equation are in good agreement with those from classic Debye model.