Microstructures and Electrical Conduction Behaviors of Gd/Cr Codoped Bi₃TiNbO₉ Aurivillius Phase Ceramic

In this work, a kind of Gd/Cr codoped Bi₃TiNbO₉ Aurivillius phase ceramic with the formula of Bi_2.8Gd_0.2TiNbO₉ + 0.2 wt% Cr₂O₃ (abbreviated as BGTN-0.2Cr) was prepared by a conventional solid-state reaction route. Microstructures and electrical conduction behaviors of the ceramic were investigated. XRD and SEM detection found that the BGTN-0.2Cr ceramic was crystallized in a pure Bi₃TiNbO₉ phase and composed of plate-like grains. A uniform element distribution involving Bi, Gd, Ti, Nb, Cr, and O was identified in the ceramic by EDS. Because of the frequency dependence of the conductivity between 300 and 650 °C, the electrical conduction mechanisms of the BGTN-0.2Cr ceramic were attributed to the jump of the charge carriers. Based on the correlated barrier hopping (CBH) model, the maximum barrier height W, dc conduction activation energy E, and hopping conduction activation energy E were calculated with values of 0.63 eV, 1.09 eV, and 0.73 eV, respectively. Impedance spectrum analysis revealed that the contribution of grains to the conductance increased with rise in temperature; at high temperatures, the conductance behavior of grains deviated from the Debye relaxation model more than that of grain boundaries. Calculation of electrical modulus further suggested that the degree of interaction between charge carriers β tended to grow larger with rising temperature. In view of the approximate relaxation activation energy (~1 eV) calculated from Z″ and M″ peaks, the dielectric relaxation process of the BGTN-0.2Cr ceramic was suggested to be dominated by the thermally activated motion of oxygen vacancies as defect charge carriers. Finally, a high piezoelectricity of d₃₃ = 18 pC/N as well as a high resistivity of ρ = 1.52 × 10⁵ Ω cm at 600 °C provided the BGTN-0.2Cr ceramic with promising applications in the piezoelectric sensors with operating temperature above 600 °C.