Influence of mixing condition and nonstoichiometry on piezoelectric properties of (K, Na, Pb)NbO3 ceramics

To obtain a uniform mixture of raw material powders including K2CO3 and Na2CO3, the raw material powders were ball-milled in a mixture of water and methanol (first-stage mixing). After the first-stage mixing, the dried powders were mixed again by ball-milling in acetone (second-stage mixing). Samples were fabricated using the two mixing methods, one-stage mixing and two-stage mixing. In the material composition formula, (Pb0.03K0.47Nax)Nb0.994O3, the composition was changed from A-site rich to B-site rich by reducing Na content in steps of 0.01 from x = 0.50. The change in the piezoelectric properties of these samples was measured. As the B-site ion concentration exceeds A-site ion concentration, the crystal structure changed from pseudocubic to orthorhombic. The electromechanical coupling factor and remanent polarization of the samples increased in accordance with the change in crystal structure. The defect structure having A-site vacancies due to a B-site-rich composition is effective in inducing ferroelectricity.