Pressure-Induced Stabilization of Sodium Halide Perovskites

Halide perovskites with the chemical formula ABX(3) are promising materials for solar energy harvesting, with their Asite playing an important role in giving stability for the 3D corner-sharing octahedron BX6, forming the perovskite structure. In its inorganic family, the perovskite A-site is usually occupied by Cs, and when lighter atoms such as Na and K are introduced, the perovskite structure becomes unstable compared to other crystal structures. Here, we show that relatively low pressures, ranging from 6.1 to 7.0 GPa, can stabilize Na-based perovskites. We have also found that the band gap energy of these compounds decreases as a function of pressure, revealing a transition from semiconducting to metallic behavior at pressures larger than 50 GPa. These results present a pathway for the stabilization of new perovskites that can be extended to other systems composed of small ions.