Pressure-induced phase transformation of CsPbI₃ by X-ray diffraction and Raman spectroscopy

The structural transformation of cesium lead iodine (CsPbI3) has been investigated in diamond anvil cells up to ∼15 GPa at room temperature by employing synchrotron radiation X-ray diffraction and Raman spectroscopy. One reversible transformation from orthorhombic (Pnma) to monoclinic (P21/m) phase has been observed at 3.9 GPa. Isothermal pressure–volume relationship of orthorhombic CsPbI3 is well fitted by the third-order Birch–Murnaghan equation of state with K0 = 14(3) GPa, K′0 = 6(2) and V0 = 891(7) Å3. The ultralow value of bulk modulus K0 demonstrates the high compressible nature of CsPbI3, similar to those of organic–inorganic metal halide perovskites. The present results provide essential information on the intrinsic properties and stability of CsPbI3, which may be applied in photovoltaic devices.