Pressure dependence of the Raman modes for orthorhombic and monoclinic phases of CsPbI₃ at room temperature

Metal halide perovskites (MHPs) have attracted a great deal of scholarly attention in the last few decades due to their unique properties and potential for photovoltaic and optoelectronic applications. The mechanical and electrical properties of MHPs are substantially affected by altering pressure and/or temperature. Near the phase transition pressure, these properties alter dramatically and a discontinuity in the Raman frequencies is observed. In this study, the Raman frequencies of the modes were calculated as a function of pressure (at room temperature) through the isothermal mode Grüneisen parameter for these modes by using the experimental volume data from the literature for CsPbI₃. Moreover, I calculated the isothermal compressibility and the bulk modulus through the calculated Raman frequency shifts and isothermal Grüneisen parameter as a function of pressure for the orthorhombic and monoclinic phases of CsPbI₃ at room temperature. The predicted Raman frequencies, isothermal Grüneisen parameter, isothermal compressibility, and the bulk modulus for the studied modes were compared with the experimental measurements below and above the orthorhombic and monoclinic phases.