The influence on sintering and properties of sodium niobate (NaNbO3) ceramics by "non-stoichiometric" precursor compositions

NaNbO3 powders from different processing routes and various near equimolar concentrations of metal ions were sintered to ceramics and investigated concerning their structural and electric properties. The particle sizes obtained from two different conventional solid state reactions and one solvent - based route were in the range of 40 nm - 10 mm and the variation of precursor composition covered 48-52 mol% Na. Sintering temperatures were defined by the deviation from the equimolar composition between 950 and 1375 °C, which is due to the coexistence of second phases Na3NbO4, Na2Nb4O11 and NaNb3O8. Small particle sizes (40 nm-3 mm) on deviation from equimolar composition resulted in higher relative densities at lower sintering temperatures. The coexistence of second phases influences structural and electric characteristics. The former were investigated by X-ray Diffraction (XRD) for phase analysis, Scanning Electron Microscopy (SEM) for defining grain sizes and Energy-Dispersive X-ray (EDX) spectroscopy for deciding the elemental composition. The impact on electrical conductivity and dielectric properties are examined by impedance spectroscopy and the resulting d33 coefficients of 15-29 pC/N are measured by Berlincourt method.