Research Guides

 

Research

Solid State Chemistry

Research in the group focuses on the synthesis and study of novel solids which exhibit unusual electronic and magnetic behaviour. A particular area of interest is the utilization of unusual synthetic techniques and conditions to increase the degree of control and selectivity exhibited by solid state reactions, with a view to undertaking the directed synthesis of ‘designed’ solid-state compounds.

Low Temperature Solid State Synthesis

In general, the methods utilized to prepare solids employ high temperatures to overcome the considerable diffusion barriers present in most solid-solid reactions. These high temperature treatments generally result in the thermodynamic selection of reaction products (they form the most thermodynamically stable products), precluding the formation of a large number of metastable compounds which have low thermal stability. Therefore there is a need to develop synthetic techniques that will allow much lower synthetic temperatures to be used, allowing us access to reaction conditions where kinetic control can be exerted on product selection.

One approach to this problem is to utilize the observation that in many extended solid systems, one type of ion is considerably more mobile than the rest of the species which make up the phase. This mobility difference allows us to selectively insert, remove, or exchange these more mobile ions while the ‘host’ lattice remains essentially unchanged. By modifying solid-state systems in this way we can prepare highly metastable materials which are not easily prepared by conventional high-temperature synthesis routes.

Topochemical reduction to form reduced oxides and oxide-hydrides

Binary metal hydrides can be utilized to extract oxide ions from complex transition metal oxides. The resulting phases can contain transition metal cations in highly unusual oxidation states and/or coordination environments. Alternatively binary hydrides can also bring about hydride-for-oxide anion exchange to yield oxide-hydrides phases, which contain both O2- and H- anions. The lack of pi-symmetry valence orbitals on the hydride ion means that anion-ordered oxide hydride phases can have electronic band structures which are qualitatively different from their all-oxide analogues.

Soft chemical routes to ‘improper’ ferroelectric phases

Ferroelectric behaviour – the presence of a spontaneous, switchable electrical polarisation – can be induced into materials with layered perovskite-type structures by carefully controlling the cooperative tiling distortions of their constituent MO6 octahedra. Soft chemical synthesis approaches, such as anion insertion or cation substitution can be used to induce of modify ferroelectric behaviour in these phases, and in principle combine ferroelectricity with magnetism to yield magnetoelectric multiferroic behaviour.  

Selected Publications

LaSr3NiRuO4H4: A 4d transition-metal oxide-hydride containing metal hydride sheets.
L. Jin, M. Lane, D. Zeng, F. K. K. Kirschner, F. Lang, P. Manuel, S. J. Blundell, J. E. McGrady and M. A. Hayward
Angewandte Chemie, 57 (2018) 5025.

Theory and neutrons combine to reveal a family of layered perovskites without inversion symmetry.
T. Zhu, T. Cohen, A. Gibbs, W. Zhang, P. S. Halasyamani, M. A. Hayward and N. A. Benedek
Chemistry of Materials, 29 (2017) 9489.

The role of π-blocking hydride ligands in a pressure-induced insulator-to-metal phase transition in SrVO2H.
T. Yamamoto, D. Zeng, T. Kawakami, V. Arcisauskaite, K. Yata, M. Amano Patino, N. Izumo, J. E. McGrady,
H. Kageyama and M. A. Hayward
Nature Communications, 8 (2017) 1217.

A Coupled Electronic and Magnetic Phase Transition in the Infinite-Layer Phase LaSrNiRuO4.
M. Amano Patino, D. Zeng, R. Bower, J. E. McGrady and M. A. Hayward
Inorganic Chemistry, 55 (2016) 9012.

Professor M.A. Hayward

Professor of Inorganic Chemistry

Inorganic Chemistry

michael.hayward@chem.ox.ac.uk

Telephone: 44 (0) 1865 272 623

Research Group Website

http://research.chem.ox.ac.uk/michael-hayward.aspx