Processing and electrical properties of KNbO3 ferroelectric dense ceramics added with small amount of Bi2O3 and MnCO3

Doping a small quantity of additive Bi2O3 is effective in suppressing the deliquescence of KNbO3 ceramics. When an optimized ball-milling process was included, dense and nondeliquescent KNbO3 ceramics were obtained by a conventional firing process. However, the presence of Bi prevented grain growth (< 0.2 mu m) and it was one of the causes of low ferroelectricity. Moreover, the insufficient resistivity made the poling treatment difficult. In order to improve the electric properties, a small quantity of additive MnCO3 was also doped into KNbO3 with 0.5 mass% Bi2O3. Codoping of KNbO3 with MnCO3 and Bi2O3 (abbreviated to KNBixMny; x = 0-1.0, y = 0-1.0 in mass%) improved the ferroelectricity of samples, and it also had an effect on the resistivity and densification of sintered bodies. Well-saturated P-E hysteresis loops were observed with any amount of Mn and the largest remanent polarization P-Gamma was about 16 mu C/cm(2). The piezoelectric properties of KNBi0.5Mn0.3, which had the highest piezoelectricity in this study, are an electromechanical coupling factor k(33) and piezoelectric constant d(33) of 0.30 and 101 pC/N, respectively.