Dielectric Properties and DC Bias Characteristics of BaTi_1-mZr_mO₃-x mol.% MgO-4.5 mol.% Gd₂O₃-2 mol.% SiO₂ Ceramics

In this study, BaTi_1-mZr_mO₃-4.5 mol.% Gd₂O₃-2.0 mol.% SiO₂ ceramics with different Zr/Ti ratios and MgO contents were prepared via solid-state reaction. The MgO addition decreased the densification temperatures of the ceramics and increased the second phase Ba₂GdZrO_5.5 content. The temperature coefficient of capacitance curves of the ceramics had an almost linear variation with temperature, with negative temperature coefficients. With the increase of the Zr⁴⁺/Ti⁴⁺ ratio and MgO content, the temperature coefficient of capacitance rotated counter clockwise due to the lower T_m temperature, and a smaller tan δ and a higher electrical resistance were obtained at room temperature. The Zr⁴⁺ ion replacement and MgO addition reduced the TiTi′ concentrations, and therefore, lessened the hopping conduction between Ti⁴⁺ and Ti³⁺ ions, while excess MgO produced VO∙∙ and had an opposing effect. Additionally, larger amounts of MgO led to smaller grain sizes, and thus, more insulating grain boundaries. The change in the dielectric constant with the bias field, a typical nonlinear dielectric behavior, decreased with increasing MgO content and Zr⁴⁺/Ti⁴⁺ ratio. For BaTi_0.70Zr_0.30O₃ ceramics with additives of 6 mol.% MgO, 4.5 mol.% Gd₂O₃, and 2 mol.% SiO₂, the dielectric constant changed by a minimum value of 0.37% under a bias of 2.5 kV/mm.