The effect of processing conditions on the dielectric properties of SBN ceramics

Strontium Barium Niobate (BN) compositions SrxBa1-xNb2O6, 0.25 less than or equal to x less than or equal to 0.75 have been co-doped with titanium (Ti) and tungsten (W). Attention has been focused on compositions in the range 0.30 less than or equal to x less than or equal to 0.40, with dopant concentrations, y, in the range 0.00 less than or equal to y less than or equal to 0.20, corresponding to the overall composition SrxBa1-xNb2-2yTiyWyO6. Whereas undoped SBN exhibits a relaxer type of ferroelectric response, the tungsten and titanium dopants were added in order to investigate if a change to a 'normal' ferroelectric response could be effected. Two sets of experiments have been carried out to date: (i) synthesis and characterisation of ceramics with x = 0.35 and 0.00 less than or equal to y less than or equal to 0.10 from industrial grade reactants; and (ii) a more complete study, from high purity precursors, with 0.30 less than or equal to x less than or equal to 0.40 and 0.000 less than or equal to y less than or equal to 0.700. Initial results show that the dielectric response of these materials is highly sensitive to processing conditions, i.e. calcination and sintering times. Furthermore, SEM/EDAX analysis suggests the presence of additional phases alongside the parent tetragonal tungsten bronze phase which is characteristic of SBN. An experimental strategy is defined for elucidating the effects of varying chemical composition and processing conditions on both phase stability and dielectric properties.