Influence of the lengthscale cation mixing degree on the nonlinear dielectric properties of BaZrxTi1-xO3 ceramics

BaTiO3-based ceramics are attractive as Pb-free relaxors with applications in microelectronics and wireless communications. The homovalent substitution with Zr4+ ions shifts the Curie temperature below room temperature and bring high values of permittivity in desired temperature ranges, but also to significantly broaden the ?(T) dependence. The Zr/Ti ratio is a very important parameter in the BaZrxTi1-xO3 (BZT) solid solutions which tailors the ferro-paraelectric phase transition type, its characteristic temperature and functional properties. However, various dielectric properties were reported for similar BZT compositions and this raised the question about the possible role of the Zr and Ti cation distribution and mixing degree inside the ceramic body. In the present work, BZT ceramics with nominal compositions x=0.05; 0.1; 0.15; 0.2 and 0.4 and with different Zr/Ti mixing levels were prepared by solid state reaction from: (i) oxide precursors (BaCO3, TiO2 and ZrO2), then calcined to promote the perovskite phase formation; (ii) by mixing in appropriate proportions perovskite BaTiO3 and BaZrO3 powders to produce a solid solutions in which the Zr/Ti mixing degree is expected to be lower than in previous case. After calcination all the powders were sintered at 1500°C for 4 hours. Dense ceramics (relative density above 95-98%) and homogeneous microstructures have been obtained for all the compositions. Impedance spectroscopy in the temperature range of (-150 to 150)°C shows a composition-dependent shifts of the structural transition temperatures by comparison with ones of the pure BaTiO3 (Fig.1 a). The permittivity vs. dc field data was determined at room temperature. The nonlinear characteristics of the samples with same composition and different mixing level show a modification in permittivity values, together with a slight increase of the tunability.