High-Pressure Studies on the Structures and Physical Properties of Lead Halide Perovskites and Metal Hydrides

Abstract

High-pressure physics is an increasingly fast-paced and interdisciplinary field with huge implications for the industry and fundamental research. Pressure affects intermolecular interactions and interatomic properties. Under extreme conditions, materials exhibit properties that can be remarkably different from those observed in ambient conditions. This dissertation focuses on the high-pressure study of two attractive classes of materials, lead halide perovskites and metal hydrides. The dissertation is divided into seven chapters, whereas Chapters 1 and 7 give a brief introduction and conclusion. Chapter 2 provides a detailed explanation of the methods and techniques used for the research. The results are presented in the remaining chapters (Chapters 3-6). Lead halide perovskites (LHPs) have been extensively studied over the last decade, with various compositions, dimensionalities, electrical and optical properties, leading to an emergence of high-performance photovoltaic and optoelectronic applications. The soft lattices of LHPs render them sensitive to mechanical compression, which can effectively adjust their atomic and electronic structures and physical properties without changing their chemical composition. The first part of this dissertation, including Chapters 3 and 4, focuses on investigating composites of zero- and three-dimensional LHPs under high pressure. The structure-property correlation of multi-dimensional LHPs under high pressure is explored. Metal hydrides have existed and been potentially used in many applications, such as batteries, hydrogen storage, and superconducting materials. Searching for new metal hydrides and a better understanding of the behavior of known metal hydrides could prove crucial in the realization or further development of these applications. In the latter part of this dissertation, Chapters 5 and 6 aim to synthesize and investigate the electrical properties of new metal hydrides under extreme conditions. The high-temperature tungsten hydride phase fcc-WHx was observed for the first time. The formation and electrical properties of the iron-doped cobalt hydride structure were demonstrated.