Pressure-induced phase transitions of CsSnBr3 perovskite from first-principles calculations

Abstract High-pressure structure transition of nontoxic all-inorganic MHP CsSnBr 3 was fully explored up to 15 GPa using an advanced structure search technique CALYPSO combined with first-principles calculations. Besides the known orthorhombic Pnma ground state phase, two high-pressure semiconducting Cmcm and P 2 1 / m phases of CsSnBr 3 were firstly uncovered above 2.37 and 6.8 GPa, respectively. Both phase transitions of the Pnma → Cmcm at 2.37 GPa and Cmcm → P 2 1 / m at 6.8 GPa were characterized as first order with a volume reduction of 4.7% and 10.8%. The occurrences of high-pressure Cmcm and P 2 1 / m phases follow the enhanced distortions of Sn–Br polyhedrons and increased coordination of Sn atoms from 6 to 8 at elevated pressures. Compared to the direct band gap of the ambient-pressure Pnma phase, the Cmcm and P 2 1 / m phases exhibit a larger indirect band gap of 2.347 and 3.143 eV, respectively, originating from the movement away from the Fermi level of conduction bands driven by the twisting of Sn–Br polyhedrons under pressure. The light absorption performances of two high-pressure phases in comparison with the Pnma phase were studied by the calculated optical absorption coefficients.