Preparation of DC-bias-free (Ba, Sr)TiO₃-Bi(Mg, Ti)O₃-NaNbO₃ Ceramics with Reduced Temperature Dependent Dielectric Properties

Abstract

(1-2x)(Ba 0.8 Sr 0.2 )TiO 3 -x(Bi(Mg 0.5 Ti 0.5 )O 3 -NaNbO 3 ) (x = 0 -0.33) ceramics were prepared by solid-state synthesis and the dielectric properties were investigated. At x = 0, the ceramics showed a ferroelectric behavior, and thus the dielectric properties were strongly dependent on electric field and temperature. With increasing x, the ferroelectric behavior became weak, and the electric field and temperature dependence became smaller. For the ceramics with x = 0.25 and 0.33, the dc bias and temperature dependence of the dielectric constant was small, that is, the dielectric constant was 310 -573 under dc bias fields of 0 -180 kV/cm and temperatures of 25 -400 ˚C. Moreover, at x = 0.33, the grain size dependence was also small; the dielectric constant at 25 ˚C and no dc bias was 481 -561 at grains sizes of 1.0 -3.2 µm. These stable dielectric properties indicated that the ceramics could be candidate materials for high temperature, dc-bias-free capacitor applications. [5] are candidate materials for capacitors operating at high electric field and high temperature. This is because polarization electric field loops were less hysteretic and rather linear and thus the dc bias dependence of the dielectric constant was reduced. On the temperature dependence of the dielectric constant, a characteristic broad peak was observed for the solid-solutions, which led a temperature-stable dielectric constant from 200-400˚C, although a strong dielectric dispersion was observed near room temperature. Recently, in the BT-Bi(Zn 1/2 Ti 1/2 )O 3 system, this problem of the dielectric dispersion was circumvented by addition of NaNbO 3 (NN) to lower the temperature that the dielectric properties became strongly frequency dependent [6].In this study, the ceramics of the (Ba 0.8 Sr 0.2 )TiO 3 (BST)-BMT-NN ternary system with the focus of (1-2x)BST-x(BMT-NN) compositions were prepared, and the dielectric properties were investigated. Here, Ba was substituted with Sr to further stabilize the dielectric properties near room temperature by lowering the Curie temperature of BT. Effect of the grain size on the dielectric properties including the dielectric breakdown