Quantitative microstructural analysis and piezoelectricity of highly dense, submicron-structured NaNbO3 ceramics from mechanically activated precursors

We study in this work the processing of NaNbO3 ceramics prepared in a single thermal treatment of highly reactive precursors obtained by mechanical activation of different reagents, aiming to determine optimum conditions for piezoelectric ceramics production. Pressure-less sintering at 1200 °C leads to dense ceramics (<5% porosity) with poor mechanical stability, unsuitable for practical uses. Dense hot-pressed ceramics were also obtained at lower temperatures (900-1100 °C), all of them in the submicron range of average grain sizes (<400 nm). Their microstructure was quantitatively characterized and their elastic and electromechanical properties determined by an automatic iterative method from impedance measurements at resonance. A noticeable ensemble of piezoelectric and elastic properties (d33 = 38 pC N−1 and Np = 3252 kHz mm) was measured for hot-pressed ceramics, from precursors obtained by a combined route of wet-chemistry and mechanical activation, with a microstructure characterized by 0.4% residual porosity and a bimodal lognormal distribution of grain size.