Effect of MnO2 on the dielectric and piezoelectric properties of alkaline niobate based lead free piezoelectric ceramics

Lead free ferroelectrie ceramics of the KNN-LiTaO3-LiSbO3 system were prepared using the mixed oxide route. This work reports the effect of doping (K0.44Na0.52Li0.04)(Nb0.86Ta0.1Sb0.04)O-3 produced through the conventional solid state sintering method with different amounts of MnO2. With 1 mol% of the dopant, similar to 96.5% of the theoretical density of the ceramics was achieved while grain growth inhibition was attained through pinning of the grain boundary movement. A polymorphic phase transition (PPT) was induced in the ceramic from the orthorhombic crystal structure to the tetragonal structure with increasing dopant amount. At lower temperatures, the doped samples had higher epsilon values but there was a decrease in both T-c (from 333 degrees C to 249 degrees C) and epsilon value at T-c (from approximate to 9500 to <6000). At temperatures below 300 degrees C however, the loss tangent in the doped samples (approximate to 2.5 mol%) was much lower and steady when compared to the undoped one. The ferroelectric properties were slightly lowered with the addition of MnO2. The remnant polarisation (P-r) was lowered from similar to 18 mu C/cm(2) to similar to 9 mu C/cm(2), the coercive field (E-c) from similar to 8.5 kV/cm to similar to 6.2 kV/cm and the piezoelectric charge coefficient (d(33)) decreased as well. (C) 2008 Elsevier Ltd. All rights reserved.