Work

Temperature and Pressure Effects on Phase Transitions and Structural Stability in CsPb 2 Br 5 and CsPb 2 Br 4 I Perovskite-Derived Halides

Year: 2024

Type: article

Abstract: All-inorganic perovskites exhibit outstanding light absorption properties in the visible range suitable for solar energy applications. We focus on the synthesis of CsPb 2 (Br,I) 5 using mechanochemical procedures. Synchrotron X-ray diffraction (SXRD) data are essential for determining the crystallographic evolution in the 295–753 K temperature range. From room temperature to 573 K, the crystal structure is refined in a two-dimensional (2D) tetragonal framework (space group: I 4/ mcm ) consisting of layers of face sharing [Pb(Br,I) 8 ] polyhedra. Above a transition temperature of T t = 630 and 621 K, identified from differential scanning calorimetry (DSC) curves for CsPb 2 Br 5 and CsPb 2 Br 4 I, respectively, a cubic three-dimensional (3D) corner-sharing perovskite structure is identified, showing substantial Cs and (Br,I) deficiency. A more ionic character for Cs-halide versus Pb-halide is derived from the evolution of the anisotropic atomic displacements. An ultralow thermal conductivity of 0.35–0.18 W m –1 K –1 is related to the low Debye temperatures. From high-pressure SXRD studies, the change in B 0 can be attributed to a basic expansion of the unit-cell volume caused by the chemical pressure from iodine within the CsPb 2 Br 5 framework. UV–vis–NIR spectroscopy revealed optical gaps of approximately 2.93 and 2.50 eV, respectively, which agrees with ab initio calculations.

Source: Inorganic Chemistry

DOI: 10.1021/acs.inorgchem.4c03920