Effects of the phase transition on the structural, mechanical, electronic and vibrational properties of the CaSnO₃ perovskite: Study under hydrostatic pressure

For this work, a theoretical study was carried out on the CaSnO₃ perovskite, under hydrostatic pressure, in the Density Functional Theory framework. The CASTEP code was used for calculations made within the Generalized Gradient Approximation. The results for the lattice parameters (at zero GPa) agree with the experimental and theoretical data available elsewhere. Enthalpy calculations show a hydrostatic pressure-induced phase transition (P_T): from perovskite to post-perovskite (Pbnm to Cmcm), at 20 GPa. As the hydrostatic pressure increases, the lattice parameters and the Sn–O bonds lengths decrease; however, at P_T, the bond lengths increase. Above P_T, the bond length distance decreases as the hydrostatic pressure increase, and, consequently, the orthorhombic distortion increases at P_T. On the other hand, the values for the independent elastic constants, the mechanical modules and the Debye temperature increase under pressure, whereas the hardness decreases. By means of the Born's structural stability criteria it was identified that the Pbnm and Cmcm phases are mechanically stable, while the Pugh's and Poisson criteria suggest ductile behavior from zero to 60 GPa and interatomic central forces' contribution, respectively. The electronic properties at zero GPa show that the Pbnm phase has a bandgap around 4.34 eV; at P_T, the value of the bandgap increases up to 5.51 eV. For the Cmcm phase, the bandgap value at P_T is 5.29 eV and increases to 5.67 at 60 GPa. As a general result, the value of the bandgap increases with the pressure. Finally, the vibrational properties show that the systems are stable at zero and 60 GPa. Then, the CaSnO₃ perovskite could be used as an anode for electrochemical systems due to their electronic properties and because their resistance increases with the pressure.