Microstructural and Electrical Characterisation of La_xBa_1-xTi_1-xY_xO₃ (0≦ x≦ 0.50) Ceramics

Abstract

LaxBa1-xTi1-xYxO3 (0≤x≤0.5) powders were synthesised in air at 1400°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 Pm3m). 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 (τf=+12 ppm/K) and although they resonate at microwave frequencies they have low quality factors (Q.f≤ 755 at ~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-xYxO3 ceramics.