Study of ferroelectric-relaxor BaCexTi1-x O3 ceramics

BaTiO 3-based ceramics are attractive as Pb-free relaxors with applications in microelectronics and wireless communications. Among the dopant ions, cerium is a special element with two oxidation states: Ce 3+ and Ce 4+ , that can be incorporated at Ba-site (as Ce 3+ ), while Ce4+ will be preferentially incorporated on Ti-sites. In the present paper, single phase dense (98-99% relative density) BaCexTi1-x O3 (x = 0.02; 0.05; 0.10 and 0.20) ceramics were prepared by a conventional ceramic processing consisting of four fundamentals steps: preparation of the powder by solid state reaction, consolidation of the powder by isostatic pressing, sintering of the powder compact into a dense polycrystalline ceramic, cutting and polishing. The mixed powders have been calcined at 1000 °C for 4h and sintered at 1450 °C for 4h, resulting in dense single phase ceramics with homogeneous microstructures. The sample with 20% of Ce needed a sintering treatment at 1550 °C to become dense enough. X-ray diffraction on calcinated powders and sintered ceramics showed the formation of perovskite single phase BaTi1-xCexO3. The microstructural features (density, grain size and grain size distribution) of the dense ceramic were determined from SEM images. Impedance spectroscopy in the temperature range of (20 to 180) °C shows a composition-induced ferroelectric-to-relaxor crossover with compositional-dependent shifts of the structural transition temperatures by comparison with ones of the pure BaTiO3. The dielectric characteristics indicate the possibility of either superposition of phases and/or the possible partial doping of Ce3+ on A positions. The nonlinear dielectric properties of ceramic samples were investigated at room temperature and the results were discussed in term of ferroelectric-relaxor crossover induced by composition. Acknowledgements: This work was performed in the frame of COST Action IC1208.