Nanostructure in Functional Ceramics

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The functional properties of many ceramics are controlled principally by displacements of ions which create small electric dipoles across the unit cells of certain types of oxides. However, in order for these electric dipoles to affect the bulk properties, they must be cooperative, i.e. the displacemetns must occur in the same direction for at least several tens of unit cells. Functional properties are tailored for a specific application by modifying the direction and length over which the dipoles are cooperative as well as the temperature at which they occur (Tc). In ceramic capacitors which act as rf filters, a mesoscale heterogeneous distribution of dopants modifies the magnitude, direction and onset temperature of the dipoles, preventing the filter frequency from changing significantly with temperature. In piezoelectric ceramics, a nanoscale mixture of monoclinic, tetragonal and rhombohedral phases in which the direction/magnitude of the dipoles differs in each structure, optimises the charge/displacement produced. This programme aims to investigate the local nanostructure of ceramics using advanced analystical instrumentation and determine its relation to bulk properties (permittivity, dielectric loss, piezoelectricity). This understanding will be used to improve performance and develop new functional ceramics.