New and Improved Electroceramics

This Large Grant proposal combines the expertise of Sheffield and Leeds to establish a major electroceramics research hub. Electroceramics are advanced materials whose properties and applications depend on close control of crystal structure, chemical composition, ceramic microstructure, dopants and dopant (or defect) distribution. In most cases, properties depend on a complex interplay of structural, processing and compositional variables. They find applications in various physical forms, eg as ceramic discs, thick and thin films and multi-layer devices consisting of alternating layers (up to several hundred) of ceramic and metal electrodes. The particular property of interest may be a bulk property of the crystals, for example, high levels of ionic conductivity, mixed electronic-ionic conduction, ferro-, pyro- piezo-electricity or ferrimagnetism. Alternatively, it may relate specifically to the grain boundaries (or surface layers) in polycrystalline materials and to small differences in composition and therefore electrical behaviour between the bulk and grain boundary (or surface) regions. Such heterogeneous, or functionally-graded ceramics find many applications eg non-ohmic devices in current limiters such as varistors and thermistors. This proposal focuses on new and improved electroceramics for potential near- and long-term applications. The work will be carried out by a multidisciplinary team with complementary skills in materials discovery, modelling, processing and advanced characterisation. Such a multifaceted approach to electroceramics research and development does not exist in the UK within a single institution and the establishment of a 'hub' between the two universities will allow us to compete with the best in the world. Three work packages are proposed.I. New and improved bulk materials: structure-property relations, including: (a) novel perovskite-type materials with targeted functionality: ferroelectricity, reversible electro-strain, piezoelectricity, magneto-electric coupling and mixed conductivity; (b) development of new low temperature co-fired ceramics based on Sillenites; (c) oxygen nonstoichiometry and core-shell phenomena in doped BaTiO3; (d) development of improved lithium battery cathodes based on layered rock salt structures. II. Materials processing and development in thin and thick film form, including:(a) BiFeO3-PbTiO3 and BiMeO3 thin films for ferroelastic/ferroelectric switching for actuator and memory applications; (b) thin film feasibility studies on Solid Oxide Fuel Cell structures; (c) thick and thin films based on the novel ferroelectric system Ba2RETi2Nb3O15 to assess their potential device applications; (d) development of a masked Electrophoretic Deposition technique to deposit planar magnetoelectric composites based on Pb(Zr,Ti)O3-Pb(Ni,Nb)O3 (soft piezoelectric) and (La,Ca)MnO3 (magnetostrictor). III. Modelling of bulk materials and interfacial phenomena: (a) Development of Finite Element modelling of current pathways in (i) heterogeneous ceramics, (ii) local probe measurements within grains and across individual grain boundaries and (iii) multilayer devices; the results will be used to simulate Impedance Spectroscopy data and allow comparison with, and interpretation of, experimental data; (b) Modelling of functional oxides: point defects, electronic band structure calculations and mass diffusion in ceramics; this will underpin the experimental programmes on the development of new materials and the role of dopants in existing materials. Work packages I and II will be supported by a wide range of characterisation techniques available at Leeds and Sheffield for studying bulk and interfacial phenomena. New characterisation techniques will be applied: aberration-corrected TEM allows true atomic scale spectroscopy of interfaces and defects; Kelvin Probe Microscopy gives direct imaging of the work function variation in grain and across grain boundary regions.