InBO3 and ScBO3 at high pressures: An ab initio study of elastic and thermodynamic properties

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We have theoretically investigated the elastic properties of calcite-type orthoborates ABO3 (A=Sc and In) at high pressure by means of ab initio total-energy calculations. From the elastic stiffness coefficients, we have obtained the elastic moduli (B, G and E), Poisson's ratio (ν), B/G ratio, universal elastic anisotropy index (AU), Vickers hardness, and sound wave velocities for both orthoborates. Our simulations show that both borates are more resistive to volume compression than to shear deformation (B>G). Both compounds are ductile and become more ductile, with an increasing elastic anisotropy, as pressure increases. We have also calculated some thermodynamic properties, like Debye temperature and minimum thermal conductivity. Finally, we have evaluated the theoretical mechanical stability of both borates at high hydrostatic pressures. It has been found that the calcite-type structure of InBO3 and ScBO3 becomes mechanically unstable at pressures beyond 56.2 and 57.7GPa, respectively.