Gd/Mn Co-Doped CaBi₄Ti₄O₁₅ Aurivillius-Phase Ceramics: Structures, Electrical Conduction and Dielectric Relaxation...

In this work, Gd/Mn co-doped CaBi₄Ti₄O₁₅ Aurivillius-type ceramics with the formula of Ca_1-GdBi₄Ti₄O₁₅ + xGd/0.2wt%MnCO₃ (abbreviated as CBT-xGd/0.2Mn) were prepared by the conventional solid-state reaction route. Firstly, the prepared ceramics were identified as the single CaBi₄Ti₄O₁₅ phase with orthorhombic symmetry and the change in lattice parameters detected from the Rietveld XRD refinement demonstrated that Gd³⁺ was successfully substituted for Ca²⁺ at the A-site. SEM observations further revealed that all samples were composed of the randomly orientated plate-like grains, and the corresponding average grain size gradually decreased with Gd content (x) increasing. For all compositions studied, the frequency independence of conductivity observed above 400 °C showed a nature of ionic conduction behavior, which was predominated by the long-range migration of oxygen vacancies. Based on the correlated barrier hopping (CBH) model, the maximum barrier height W, the dc conduction activation energy E_dc, as well as the hopping conduction activation energy E_p were calculated for the CBT-xGd/0.2Mn ceramics. The composition with x = 0.06 was found to have the highest E_dc value of 1.87 eV, as well as the lowest conductivity (1.8 × 10^-5 S/m at 600 °C) among these compositions. The electrical modules analysis for this composition further illustrated the degree of interaction between charge carrier β increases, with an increase in temperature from 500 °C to 600 °C, and then a turn to decrease when the temperature exceeded 600 °C. The value of β reached a maximum of 0.967 at 600 °C, indicating that the dielectric relaxation behavior at this temperature was closer to the ideal Debye type.