Understanding the impact of gadolinium substitution on the impedance and conduction mechanism of barium zirconium titanate ceramics

In the present paper, we investigate the structural and electrical properties of gadolinium (Gd)-modified barium zirconate titanate (BZT) ceramics, i.e., Ba_1-xGd_2x/3Zr_0.05Ti_0.95O₃ (BGZT; x = 0.01–0.05). The high-temperature solid-state reaction method has been used to synthesize the ceramics. The X-ray diffraction and Rietveld refinement analysis show the existence of dual-phase tetragonal (P4mm) and orthogonal (Amm2) in all the compositions. In the XRD data, the peak shifts to a lower angle up to x = 0.03 and then toward the higher angle side indicating the doping at the A site for (x ≤ 0.03 and at the B site for higher concentration. The grain size is found to be reduced from around ~ 2 μm to ~ 0.5 μm with Gd doping. The real and imaginary impedance values increase to 0.8 MΩ for x = 0.03 and then reduce for higher concentrations. The complex impedance spectra indicate that the grain and the grain boundary resistance are decreasing with increasing concentrations of Gd until x = 0.03 with a minimum value of ~ 40kΩ (at 300 ℃) and then rising for higher concentrations. The excellent fitting of the Kohlrausch–Williams–Watts function to the dielectric modulus indicates the transition from long-range to short-range mobility of charge carriers. The temperature-dependent ac conductivity shows that the conductivity rises until x = 0.03 and then reduces due to the incorporation of Gd in the Ti site producing oxygen vacancies. The activation energy for both the conduction and relaxation processes was obtained using the Arrhenius plots. The activation energy for the relaxation process is less than ~ 0.5 eV and for the conduction process found to be more than ~ 0.5 eV indicating different hoping mechanisms are involved in the composition.