Dielectric and piezoelectric properties of the KNN ceramic compound doped with Li, La and Ta

With the purpose of improving the dielectric and piezoelectric properties of (K0.5Na0.5)NbO3 (KNN), a multiple doping strategy was tested in this research. Piezoceramics with composition [(K0.5Na0.5)(0.94)Li-0.06](0.97)La-0.01(Nb0.9Ta0.1)O-3 were prepared by the traditional ceramic method. The calcined powders were sintered in their own atmosphere at 1,100 A degrees C for 1.0, 1.5 and 2.5 h. X-ray diffraction analysis showed that the Li+, La3+ and Ta5+ cations diffuse into the KNN structure to form a perovskite-structured solid solution. For 1 h sintering time, a dominant orthorhombic phase is obtained, whereas for the longer times, the dominant phase was tetragonal. The presence of a tetragonal tungsten-bronze minority second phase is confirmed. Scanning electron micrographs show rectangular-shaped grains with a mean size of 1.1 +/- A 0.2 mu m. The existence of pores and traces of a liquid phase favoring grain growth and homogeneity is also observed. Experimental results show an enhancement of the permittivity associated with the enlargement of the c parameter of the cell that increases with sintering time. Li+ incorporation into the structure is made evident by its transition temperature at 400 A degrees C different from those of KNNLaTi (81-110 A degrees C) and KNNLaTa (340 A degrees C). An analysis of the phase transition of the samples indicates a normal rather than a diffuse transition. The electromechanical parameters k (p), Q (m), sigma (p), s (11), d (31) and g (31) are determined and compared to those of commercial PZT ceramics.