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 1200oC leads to dense ceramics (<5% porosity) with poor mechanical stability, unsuitable for practical uses. Dense hot pressed ceramics were also obtained at lower temperatures (900-1100oC), all of them in the submicron range of average grain sizes (< 400 nm). Their microstructure was quantitatively characterised 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.