Enhanced temperature stability and reduced tan δ in B-site modified titanate-based high-entropy perovskite oxides

Abstract

The dielectric properties of complex titanate perovskites are highly sensitive to the composition, which influences the stability of the ferroelectric state. This work examines the role of Zr⁴⁺ and (Mg_1/3Nb_2/3)⁴⁺ doping on the B-site in a high entropy composition based on (Na_0.2Bi_0.2Ba_0.2Ca_0.2Sr_0.2)TiO₃. In particular, (Na_0.2Bi_0.2Ba_0.2Ca_0.2Sr_0.2)(Ti_1−xMe_x)O₃ (Me = Zr⁴⁺, (Mg_1/3Nb_2/3)⁴⁺, x = 0.00–0.15) ceramics are synthesized by solid-state reaction method. All ceramics form a single-phase cubic structure as demonstrated by X-ray diffraction. The difference in ionic radius between Zr⁴⁺ and (Mg_1/3Nb_2/3)⁴⁺ ions contributes to changes in lattice parameter and microstructure. The Zr⁴⁺ doping generally causes lattice expansion, whereas low concentrations of (Mg_1/3Nb_2/3)⁴⁺ doping lead to lattice contraction, resulting in distinct microstructural modifications. For the doped samples, the relative permittivity decreases due to the influence of the dopants when compared with the undoped sample. Furthermore, the dielectric loss decreases substantially to a value below 0.001 across a broad temperature range and the temperature stability of capacitance is enhanced at elevated temperatures. Furthermore, all ceramics with higher Zr⁴⁺ and (Mg_1/3Nb_2/3)⁴⁺ concentrations show linear dielectric behavior with evidence of significant change of electrical characteristics revealed by impedance and modulus analysis. Consequently, the addition of Zr⁴⁺ and (Mg_1/3Nb_2/3)⁴⁺ to the composition (Na_0.2Bi_0.2Ba_0.2Ca_0.2Sr_0.2)TiO₃ shows great promise for high temperature, temperature stable capacitor applications.