5d Transition Metal Oxyhydrides

Lead Research Organisation: University of Oxford
Department Name: OxICFM CDT

Abstract

Transition metal oxyhydrides are uncommon materials that contain both oxide and hydride ions in the anion lattice. Due to the contrasting features of the two ions, they exhibit a range of interesting properties that would not be accessible to metal oxides. The lower charge of the hydride ion relative to oxide ions stabilises transition metals with lower oxidation states than are typically observed for metal oxides, whilst the lower electronegativity and higher polarizability of hydride ions relative to oxide ions can result in increased covalency and stronger magnetic interactions. In addition, the symmetry of hydride ions is different from oxide ions, which can dramatically affect the orbital connectivity within the material and lead to materials with reduced dimensionality in their electronic structure. As such, transition metal oxyhydrides often have fundamentally different chemical and physical properties to the corresponding oxides. As a result of their unusual chemical behaviour, oxyhydrides could become an important class of functional material with potential applications in hydrogen fuel cells or as catalysts in ammonia synthesis.
Due to the strongly reducing nature of the hydride ion, transition metal oxyhydrides are generally thermodynamically unstable with respect to the elemental metal and water, so preparing these materials through conventional high temperature ceramic synthesis methods is unfeasible. As such, soft chemistry methods are required to synthesise transition metal oxyhydrides as metastable phases, whereby hydride ions are inserted directly into a parent crystal structure at low temperature. Recently, these methods have been used to synthesise a number of oxyhydrides containing 3d and 4d transition metals. Many of these were found to exhibit novel electronic and magnetic properties, and they often adopt structures containing MH2 or MO2 sheets, which are analogous to the CuO2 sheets found in cuprate superconductors.
This project aims to prepare the first oxyhydrides that contain 5d transition metals. In contrast to previously prepared transition metal oxyhydrides, the strong spin-orbit coupling and wide bands associated with 5d metals are expected to yield materials with qualitatively different chemical and physical properties to lighter transition metal analogues, which could lead to desirable features, such as superconductivity or magnetoresistivity. In addition, due to the delicate balance of interactions that localise and delocalise electrons in 5d transition metal compounds, small alterations in the crystal structure can lead to dramatic changes in the electronic and magnetic properties of the compound, thereby suggesting that a rich variety of physical behaviours are accessible in these materials. As such, these compounds are likely to provide fertile ground for the discovery of new materials with novel electronic and magnetic properties.
This project falls within the EPSRC Functional Ceramics and Inorganics research area.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S023828/1 01/04/2019 30/09/2027
2404171 Studentship EP/S023828/1 01/10/2020 30/09/2024 James Murrell