Rutile and CaCl₂ Structure of SnO₂ Phase Transition under High-Pressure Studied by First-Principles Method

In the present work we performed the first principles calculations based on the density functional theory and investigated the P42/mnm-Pnnm phase transition and the mechanical properties of SnO₂.For the exchange-correction energy we employed the generalized gradient approximation (GGA) in the Perdew, Burke and Ernzerhof (PBE) form.The elastic stiffness coefficients, c_ij, bulk modulus, shear modulus, Young modulus, Reuss modulus, Voigt modulus and anisotropy factor were calculated for two polymorphs of SnO₂:rutile and CaCl₂ structure.Our results for the structural parameters and elastic constants at the equilibrium phase are in good agreement with the available theoretical and experimental values.Using the enthalpy-pressure data, we observed the rutile to CaCl₂ structural phase transition under 11.06 GPa pressure.In the low index plane of two polymorphs' SnO₂, the most unstable and the possibility of slippage crystal planes was the {100} crystal planes of Pnnm structure, and the {001} crystal planes has the strongest binding force.The Vickers hardness calculated for the P42/mnm of SnO₂ was 10.49 GPa, and the Pnnm structure was 11.42 GPa.Because of the differences in the level of the structure symmetry, results from calculation show that the Debye temperature waverd in a small range for the utile structure but it had mutations in 8-10 GPa and showed a downward trend for the CaCl₂ structure.