2024 AIChE Annual Meeting
Analysis of Phase Transitions in Lead Halide Perovskite Cesium Lead Chloride
Understanding the reaction kinetics of a material is an integral part of its characterization. The focus of this project is on the formation of the perovskite cesium lead chloride (CsPbCl3). Materials containing a perovskite structure, such as CsPbCl3, have defect tolerance and tunable electronic properties, which make them a topic of intense research. For instance, ytterbium-doped cesium lead chloride (Yb:CsPbCl3) is a promising scintillator material for radiation conversion in detectors. The solid-state synthesis allows for easy scale-up to produce large amounts of polycrystalline scintillators. Developing an understanding for the formation allows us to better refine the synthesis as well as predict the phase transitions of the material. Interdiffusion of constituent elements is the limiting step in the conversion to the perovskite phase. Increased heating temperature and time is expected to increase the rate of diffusion and will result in a higher conversion. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were the main methods of quantifying the amount of each phase in a sample after heating. A solid state synthesis, beginning with the same composition of reactants, was utilized to create samples. Samples varied in both temperature and reaction duration in an ambient atmosphere controlled furnace. Diffraction patterns from the XRD were analyzed to determine the percent composition of the crystalline phases present in the sample by comparing relative peak intensities for the perovskite and precursors. Furthermore, an unreacted sample was measured through heating on a hot-stage in the XRD to track the phase development in-situ. Measuring the heat flow into the sample by DSC also provided an indication of the conversion of the material from its orthorhombic to cubic phase. Initial results show that as temperature and time increase in the furnace, a pure 3D phase composition encompasses the material. Additionally, the interdiffusion coefficient was determined for the precursors, CsCl and PbCl2, to understand the rate of interdiffusion of the precursor elements. To accomplish this, pellets of CsCl and PbCl2, together, were heated and measured using EDS linescans and fitted to characteristic equations. Hot-stage heating and calculating the interdiffusion coefficient are on-going. Future work looks to add the dopant Yb and quantify its diffusion characteristics in the perovskite.