Dynamical properties of metal halide and oxyhydride perovskites

Sammanfattning: This thesis concerns investigations on the dynamical properties of two classes of energy-relevant materials, namely metal halide and oxyhydride perovskites, using neutron scattering techniques. These two classes of materials share the same aspect of a perovskite-type crystal structure but are different in terms of their functional properties and concomitant promise for various technological applications.     Regarding the metal halide perovskites, these materials are of large interest for use in, e.g., next-generation solar cells and light-emitting diodes. In this thesis, the studies on these types of materials focused on elucidating the nature of organic cation and lattice dynamics in the hybrid organic-inorganic systems FA1-xMAxPbI3 (MA = methylammonium and FA = formamidinium), BA2PbI4 and PEA2PbI4 (BA = butylammonium and PEA = phenethylammonium), and the all-inorganic perovskite CsPbI3, by using a wide variety of quasielastic and inelastic neutron scattering techniques. For FA1-xMAxPbI3, a key result is that MA-doping of FAPbI3 leads to significantly different cation dynamics, which is directly related to the stabilization of the perovskite crystal structure. Overall, the results showcase the importance of organic cation and lattice dynamics and the couplings between these types of dynamics in this class of materials and highlight the importance of dynamics for an understanding of the properties of metal halide perovskites.    Regarding the oxyhydride perovskites, these materials are of interest because of their hydride ion conductivity. Here, the studies focused on elucidating the dynamical properties of hydride ions in the perovskite materials SrVO2H and BaTiO3-xHy, using quasielastic neutron scattering techniques. For SrVO2H, the results showed the presence of a correlated jump diffusion mechanism, with an enhanced jump rate for backward jumps, which slows down the long-range diffusion, and localizes hydride ions in the vicinity of a particular vacancy. For BaTiO3-xHy, a faster diffusion process was observed, which can be explained by the relatively larger amount of anion vacancies in this material, which promotes diffusion. The vibrational dynamics of hydride ions were further studied in SrVO2H. Interestingly, it was found that the V−H- and V−O-based phonons are largely influenced by the antiferromagnetic ordering of the material. These results showcase the important couplings between the magnetism and vibrational dynamics which can occur in magnetic oxyhydrides.