Research Projects: Ceramics

This list is not intended to be fully comprehensive; other topics can be negotiated with individual staff members. Additional projects will be notified in supplements issued periodically during the session. Under each major heading the projects are grouped according to the prime supervisor (with the supervisors in alphabetical order of surname).

Professor J Harding
17	SIMULATING DIFFUSION IN CERAMICS AND MINERALS Supervisor: Professor J Harding
How fast atoms move and where they end up is a major issue in understanding (and so controlling the properties of ceramics). The first is the problem of diffusion; the second the problem of segregation. This project will investigate the mechanisms of diffusion for a range of ceramics from perovskites to pyrochlores and garnets. It will also consider the segregation of atoms and ions to surfaces and grain boundaries and what difference this makes to the properties of these structures. A range of static and dynamic simulation methods will be used including /ab initio /methods. A particular objective is to link to the work of Professors Sinclair and Reaney on ferroelectrics in this Department. The codes to do the calculations are already exist, but there will be opportunities for writing scripts and codes if people are interested.
Dr N C Hyatt
18	NEW LAYERED PEROVSKITE OXIDES SHOWING MAGNETIC ORDERING AND METALLIC CONDUCTIVITY Supervisors: Dr N C Hyatt, Dr D C Sinclair and Dr P A Anderson (Uni of Birmingham)
Background. Layered perovskite oxides show interesting and technologically useful functional properties such as high temperature superconductivity (e.g. YBa₂Cu₃O₇) and collosal magneto-resistance (e.g. YBaMn₂O₅). Materials of this type comprise layers of the ABO₃ perovskite structure sandwiched between layers of a different structure type, e.g. fluorite (M₂O₂) or rock-salt (MO) layers. By controlling the number and composition of the perovskite or ‘sandwich’ layers, it is possible to “tune” the electronic and magnetic properties of such materials. Project. The aim of this project is to synthesise new layered magnetic layered perovskites, such as CsLa₂Ti_2-xMn_xNbO₁₀ or RbCa₃Nb_3-xRu_xO₁₀, where ordered substitution of a magnetic dⁿ cation for a d⁰ cation may be expected to result in a magnetically ordered material. In addition, the capacity of these materials for reductive alkali metal insertion, to form Cs_1+y La₂Ti_2-xMn_xNbO₁₀ or Rb_1+yCa₃Nb_3-xRu_xO₁₀, will also be explored with the aim accessing novel products with unusually low transition metal oxidation states and metallic conductivity. Training. This project will involve synthesis of layered perovskite oxides by high temperature solid state synthesis and reductive alkali metal insertion using glove-box techniques. The products will be characterised using range of techniques, including: X-ray, neutron and electron diffraction, electron microscopy, and Raman, X-ray absorption, electron spin and solid state nuclear magnetic resonance spectroscopies.
Professor W M Rainforth
19	HIGH RESOLUTION CHARACTERISATION OF HETEROGENEITIES IN FUNCTIONAL CERAMICS Supervisors: Professor W M Rainforth, Professor A R West, Professor D C Sinclair and Professor I M Reaney
The performance of virtually all ceramics is controlled by interfaces, which are a source of both intentional and unintentional heterogeneity. Not surprisingly, there have been a number of extensive studies of the interface structure using techniques such as HREM, ELNES, XPS etc. Many of the successful studies have been undertaken on model systems (e.g. bicrystals of SrTiO₃). Consequently, good interface structural models have been developed, but these only apply to the specific interface structure studied. Of course, real ceramics comprise a wide range of boundary types that rarely conform to the model system. The ability to characterise materials at high spatial resolution, in terms of chemical, physical and electrical structure, is currently going through a revolution. We are in a unique position to take advantage of integrating different techniques to bring a completely new insight to the microstructure/property relationships in real ceramic materials, including existing important materials such as BaTiO₃, emerging materials (e.g. CaCu₃Ti₄O₁₂), thin films, devices and new materials developed within the CCL. Techniques that will be used include: a) Scanned probe microscopy (e.g. Kelvin Probe Microscopy) to characterise local electrical structure: b) Focused ion beam microscopy (FIB) to extract specific boundaries that have been characterised by SPM for characterisation in the TEM. C) High resolution TEM to determine local chemical composition and bonding structure information at the interface of interest. The information from these techniques will be correlated with the processing and electrical characterisation of the ceramic.
Professor I M Reaney
20	PHASE TRANSITIONS IN DOPED BiFeO₃ CERAMICS Supervisor: Professor I M Reaney
It is envisaged that BiFeO₃ based thin films may be used in the next generation of ferroelectric non-volatile memories. In order to reduce the coercive field to enable 1-2V switching of the memories, BiFeO₃ is doped with various isovalent and aliovalent dopants. Currently the effect of dopants on the phase transition sequences is unknown and requires extensive investigation. In this project, RE doped BiFeO₃ ceramics will be studied utilising XRD, SEM, TEM and Raman spectroscopy. The main aim of the project will be to determine the role of reducing the perovskite tolerance factor on the phase transition sequences.
21	MICROWAVE DIELECTRIC CERAMICS FOR MOBILE COMMUNICATIONS Supervisor: Professor I M Reaney
Microwave dielectric ceramics are used in the fabrication of mobile antennas for satellite radio and global positioning systems handsets. Currently, the cost of the antennas is such that they are too expensive to be utilised routinely in 3G mobile phone hand sets. The key cost of the antenna is in the fabrication of the ceramic core and particularly the high firing temperatures required to manufacture dense low dielectric loss parts. This project aims to develop technology to reduce the cost of the antenna core by developing methods of reducing the firing temperature whilst still maintaining sufficient electrical properties for optimum performance. The project will be in collaboration with Sarantel Ltd who manufacture antennas.
22	LOCAL STRUCTURE IN PEROVSKITE STRUCTURED COMPOUNDS Supervisors: Professor I M Reaney and Professor D C Sinclair
Traditionally, crystal chemistry has relied upon macroscopic neutron and X-ray diffraction based techniques to determine the structure of complex oxides and interpret their functional properties. However, as the scale lengths in applied ceramics decrease from micro to nano and nano-scale chemical heterogeneity is increasingly used to modify properties, more advanced diffraction and spectroscopic techniques are required to determine the local structure and thereby interpret functional behaviour. This project therefore aims to study a range of perovskite structured ceramics using advanced analytical electron diffraction and Raman spectroscopy.
Professor D C Sinclair
23	EXPLORING PEROVSKITE SCIENCE Supervisors: Professor D C Sinclair, Dr N C Hyatt, Professor J Harding and Professor I M Reaney
Perovskite-based materials (general formula ABO₃) exhibit a wide range of useful electrical and/or magnetic properties, such as ferro-/ piezo-electricity, ionic/mixed conduction, metal-insulator transitions, superconductivity and giant magneto-resistance. The key to discovering and understanding these materials and the need to modify/optimise the desired property requires knowledge about the interrelationship between chemical composition, crystal structure, defect chemistry and the desired property. At Sheffield, we study the structure-composition-property relationships of a wide variety of perovskite-based materials with useful functional properties, eg BaTiO₃, Ba₃LaNb₃O₁₂, BaCo_1/3Nb_2/3O₃ and CaCu₃Ti₄O₁₂ and wish to expand our knowledge of such materials. All projects will involve some or all of the following; chemical synthesis (compositional control), crystallography (crystal structure determination), atomistic simulations (defect chemistry) and electrical/magnetic property measurements. Perovskites of interest include; B-site deficient hexagonal perovskites (A_nB_n-1O_3n), oxygen-deficient perovskites (ABO_3-d) and A or B-site ordered perovskites (A_1/4A’_3/4BO₃, AB_1/3B’_2/3O₃). Contact Prof Sinclair for further details.
24	DIELECTRIC MATERIALS FOR THE 21^ST CENTURY Supervisors: Professor D C Sinclair, Professor I M Reaney and Professor A R West
Dielectric materials (ferro-, pyro-, piezo-electrics and high permittivity, low dielectric loss solids) continue to play an important role in our every day lives, eg computer technology, smart sensors and actuators and in telecommunication devices such as mobile phones and global position systems. Despite the vast array of applications there is a constant need to improve the properties of existing dielectric materials (eg. higher permittivity, piezoelectric coefficients, ferroelectric Curie Temperature and lower dielectric loss) and to find new materials with superior properties or additional functionality (eg multi-ferroics which exhibit both ferro-electricity and ferro-magnetism). For some applications, homogeneous materials are required, whereas for others it is important to engineer chemical heterogeneity (usually by chemical doping and/or close control of oxygen partial pressure), either to create core-shell regions within grains or to produce grain boundaries and/or surface layers with different composition to the grains. In these projects, samples are prepared in the form of ceramics or films and characterised by a wide variety of techniques including; X-ray, Neutron and Electron Diffraction; Scanning, Analytical and Transmission Electron Microscopy; Impedance Spectroscopy (mHz- MHz) and/or Microwave dielectric measurements (GHz) over a wide temperature range (5- 1000K). The overall aim is establish the structure-composition-property relationships in this important class of electroceramics. Please contact Prof Sinclair for more details.
25	SOLID ELECTROLYTES FOR ELECTROCHEMICAL APPLICATIONS Supervisor: Professor D C Sinclair
Solid electrolytes are a rather rare class of solids that exhibit high levels of ionic conductivity and can be exploited in electrochemical devices. For example, oxide-ion conducting solids are used in Solid Oxide Fuel Cells (SOFCs), gas sensors and oxygen pumps. There are several structure-types known to be conducive for oxide-ion conductivity, eg defect fluorites (d-Bi₂O₃), oxygen-deficient perovskites (La_1-xSr_xGa_1-yMg_yO_3-d) and Rare Earth Apatites (La_9.33Si₆O₂₆). In all cases, chemical doping is required to optimise the electrical properties. Recently we have discovered some new Bi-based oxides with crystal structures related to Bi₂O₃ and some have high oxide-ion conductivity. This project will aim to establish the chemical composition, crystal structure(s) and electrical conductivity of these new oxide-ion conducting phases. Partial phase diagrams and chemical doping will be investigated in an attempt to optimise the oxide ion conductivity. All samples will be prepared by the mixed oxide route and characterised via X-ray and Neutron Diffraction, Electron Microscopy, Differential Scanning Calorimetry and Impedance Spectroscopy.
Professor A R West
26	NEW AND IMPROVED CATHODES FOR RECHARGEABLE LITHIUM BATTERIES Supervisor: Professor A R West
Rechargeable lithium batteries currently use intercalation cathodes based on LiCoO₂ and, more recently, LiMn₂O₄, which give reversible charge-discharge cycling at ~3.8 V and capacities of ~ 120 mAh/g. Because of the cost and environmental toxicity of Co, and the poor long-term performance of LiMn₂O₄, there is much interest in finding improved cathode materials. We are currently interested in layered rock salt structured materials, such as Li(Mn,Ni,Fe)O₂, which have high capacities and stable long-term cycling performance. These properties have not yet been optimised and their study forms the basis of the proposed project, using a combination of solid state synthesis procedures, crystal structure determination using X-ray and neutron powder diffraction, thermal analysis to assess high temperature stability, electrical property measurements to determine the intrinsic levels of both electronic conductivity and lithium ion conductivity and electrochemical testing by constructing test cells using the new materials as intercalation cathodes. We have a very well-equipped laboratory for such studies, which forms part of the EPSRC-funded Ceramics and Composites Laboratory. This is a fundamental scientific project, but outcomes are likely to be of direct relevance to the lithium battery industry.
27	IONICALLY-CONDUCTING CERAMIC ELECTROLYTES Supervisor: Professor A R West
Ceramic materials that exhibit high levels of ionic conductivity have a range of applications, depending on the conducting species, in fuel cells, battery systems and sensors. There is much interest in the discovery of new lithium-ion conducting ceramics, which, if available, could lead to the fabrication of all solid-state, thin-film lithium batteries, without containment problems associated with liquid electrolytes. Several groups of crystalline and glassy materials are of current interest, including materials with the garnet structure and other 3D framework structures. The approach to be used in this project is based on crystal engineering in which synthetic strategies are used to modify a parent crystal structure so as to open up conduction pathways by the introduction of either mobile interstitial ions or the creation of ion vacancies. The project involves a combination of synthesis by solid state reaction methods, diffraction studies to solve the structures of new phases and electrical conductivity measurements. New lithium-ion conducting solids will be tested as potential electrolytes in solid-state lithium test cells.
28	NANOCOMPOSITE ELECTROCERAMICS Supervisor: Professor A R West
Many electroceramic materials are now fabricated in thin-film form so that their properties are controlled by the ceramic microstructure and in particular, by the properties and composition of interfaces. The resulting materials are heterogeneous electrically and may be regarded as composites on the nanoscale of grains and grain boundaries that have very different electrical characteristics. This category of materials has increasing applications as ceramic sensors, voltage and current overload protection devices and charge storage materials such as barrier-layer capacitors. We are investigating several new groups of such materials with different structure types, including: BaTi₂O₅ with a complex 3D framework structure, tetragonal tungsten bronze structured phases in materials such as BaO-Nd₂O₃-TiO₂-Ta₂O₅ and the classic ferroelectric, BaTiO₃, doped with an amphoteric ion such as Ho³⁺. Projects are available in each of these areas; all involve sample synthesis, ceramic fabrication, microstructural characterisation by electron microscopy, crystallographic studies by X-ray and neutron diffraction and electrical property measurements, using a range of techniques. This project is part of the EPSRC-funded Ceramics and Composites Laboratory and may involve several members of staff in the Department for collaborative studies on, for instance, thin-film fabrication, electron microscopy and electrical property measurements.
Dr S Zhang
29	MOLTEN SALT SYNTHESIS OF CERAMICS Supervisors: Dr S Zhang
Binary, ternary and higher order oxide powders have been widely used in many areas, including engineering ceramics, electroceramics, bioceramics, catalysts and waste-treatment. Conventionally, these oxides are prepared by high temperature reaction of appropriate precursor compounds. The drawbacks of this procedure include the high temperatures and long times needed and the low reactivity and heterogeneous nature of the resulting powders. Such limitations can be overcome via using Molten Salt Synthesis (MSS) techniques. This project aims to investigate the main scientific principles underpinning this process and use the principles to synthesis several important ceramics at low temperatures. Binary and ternary oxides such as spinel, mullite, stabilised ZrO₂, CaZrO₃, BaTiO₃ and PZT, which have been extensively used in refractories and electroceramics fields, will be synthesised and their microstructures and properties characterised.
30	CARBON-CONTAINING REFRACTORY CASTABLES Supervisor: Dr S Zhang
Development and commercialisation of carbon-containing castables is a major aim of the metallurgical industries and is thus the goal of all carbon-based refractory producers. In this project, high quality (uniform, thick and strongly bonded to the substrate) carbide coatings on graphite will be prepared at a relatively low temperature. Such high quality carbide coatings will not only inhibit oxidation of graphite more efficiently than the straight addition of antioxidants, but also simultaneously improve graphites water-wettability more efficiently than other techniques used so far (e.g “sol-gel coating” and “pellet” techniques), and thus the coated graphite can be used to develop a new generation of carbon-containing refractory castables with much improved properties.
31	LOW TEMPERATURE “GREEN SYNTHESIS” OF POROUS CERAMICS Supervisor: Dr S Zhang
Porous ceramics display a unique combination of properties such as low density, low thermal conductivity, high porosity/permeability, high thermal shock resistance and high specific surface, making them indispensable for various engineering applications, including: filtration of molten metals or of particulate from exhaust gases, radiant burners, catalyst supports, biomedical devices, kiln furniture, bioreactors, supports for space mirrors, components in solid oxide fuel cells and heat exchangers. In this project, a novel and low cost “green synthesis” technique will be developed. By using biological plants (such as woods) and/or salts as templates, a range of industrially-important porous ceramics with desirable microstructures and properties will be prepared at much lowered temperatures. After preparation, microstructures of the samples will be observed using SEM/TEM and their pore size distributions examined using Hg-porosimetry and X-ray tomography. In addition, properties such as mechanical strength, thermal expansion coefficient, thermal conductivity and elastic modulus will be measured.