Preparation and properties of La doped PZT 90/10 ceramics across the ferroelectric-antiferroelectric phase boundary

Perovskite Pb1-xLax(Zr0.9Ti0.1)1-x/4O3 dense ceramics (relative density of 93-97%) with compositions across the ferroelectric-antiferroelectric boundary (x = 0.020, 0.030, 0.031, 0.032, 0.033, 0.035, 0.380, 0.040 mol.) were prepared by solid state reaction. The effect of La3+ content on the structural, microstructural characteristics and room temperature functional properties (piezoelectric and dielectric properties) of the PLZT ceramics was studied. The increasing of La3+ doping amount result in a slight decrease of ceramic grain size from 5 m to 1 m, for the same calcination and sintering parameters. The structural study evidences the formation of perovskite single-phase with rhombohedral to orthorhombic symmetry across the ferroelectric-antiferroelectric boundary. A superposition of both symmetries in the compositional range of (0.025-0.033) is demonstrated by the evolution of relative intensities I(1 1 -1)/I(1 1 1) and I(0 0 1)/I(1 0 0) splitted peaks, characteristic to rhombohedral and orthorhombic symmetries, respectively. The room temperature permittivity has a maximum for x = 0.03, while the piezoelectric constants show anomalies in the range of compositions x = (0.03, 0.035). These anomalies may be related to the phase superposition range. Polarisation vs. electric field dependence as well as the structural calculations demonstrate that these compositions transit from ferroelectric to antiferroelectric phases, with a stabilisation of the antiferroelectric phase at higher La3+ content.