First-Principles Investigation of Pressure-Induced Structural Phase Transition and Properties of CsPbF₃ Polymorphs

This study presents a first-principles investigation into the high-pressure studies of cesium lead fluoride (CsPbF₃) polymorph using the Vienna ab initio simulation package (VASP). The CsPbF₃ with <i>Pm</i>3̅<i>m</i> symmetry undergoes a pressure-induced structural transition, resulting in two distinct phases: <i>R</i>3̅<i>c</i> and <i>Pnma</i>. The structural stability, electronic structure, and optical properties of the three polymorphs of CsPbF₃ (<i>Pm</i>3̅<i>m</i>, <i>R</i>3̅<i>c</i> and <i>Pnma</i>) are investigated using the plane wave pseudopotential method within the framework of density functional theory (DFT). The elastic constants and moduli of these polymorphs were computed and the result confirms that all are mechanically stable. Electronic band structure calculations indicate that all three CsPbF₃ polymorphs exhibit semiconducting properties with a wide band gap (3-5 eV). The <i>Pm</i>3̅<i>m</i>, <i>R</i>3̅<i>c</i> form of CsPbF₃ has a direct band gap while <i>Pnma</i> form has an indirect band gap. The mechanical stability and optical properties of the <i>R</i>3̅<i>c</i> and the <i>Pnma</i> phase of CsPbF₃ have not been reported in the existing literature. By addressing this gap, this research contributes valuable data and sets the stage for future studies that explore these polymorphs in greater detail and their potential in advanced technological applications.