Microstructural and electrical characterisation of LaxBa1-xTi1-xYxO3 (0 <= x <= 0.50) ceramics

LaxBa1-xTi1-xYxO3 (0 <= x <= 0.5) powders were synthesised in air at 1400 degrees C by the conventional solid state method. According to the X-ray results, the tetragonal distortion in undoped (x=0) BaTiO3 (space group P4mm) decreases with x and samples with x >= 0.05 show cubic symmetry (space group Pm 3 m). For x >= 0.05, the lattice parameter increases linearly with x, until orthorhombic LaYO3 appears as a secondary phase for x > 0.45. Dielectric properties of dense (> 95% of the theoretical X-ray density) ceramics were studied at both radio and microwave frequencies. The permittivity maximum is shifted towards lower temperatures with increasing x and a broad permittivity peak is observed for samples with 0.05 < x < 0.30. These samples exhibit a dielectric response typical of "relaxor"-type materials. In contrast, ceramics with x=0.40 exhibit almost temperature independent dielectric properties (tau(f)=+12 ppm/K) and although they resonate at microwave frequencies they have low quality factors (Q.f <= 755 at similar to 5 GHz). Finally, conventional transmission electron microscopy combined with electron diffraction studies were carried out to provide a better understanding of structure-property relationships in LaxBa1-xTi1-xY2O3 ceramics.