Doping-induced structural, optical, and electrical modifications in (1−x)NaNbO3–xBiGdKZrO3 ceramics for microelectronic applications

A two-step sintering process was used to create ceramics composed of lead-free (1-x)NaNbO₃-xBiGdKZrO₃ (x = 0.00, 0.02, 0.04, 0.06), and their electrical, optical, and structural properties were investigated. The XRD results revealed that all of the combinations exhibited a perovskite structure, with a phase transition from orthorhombic (Pbma) to pseudo-cubic (Pm-3 m) at x = 0.04. The lattice parameters changed from a = 3.938 °C, b = 3.927 °C, and c = 3.915 °C (x = 0.00) to a = 3.952 °C, b = 3.952 °C, and c = 3.949 °C (x = 0.06), which means there is more symmetry and defects are relaxing. Raman spectroscopy revealed a peak shift from 277 to 251 cm⁻¹ and an FWHM increase from 24.96 cm⁻¹ (x = 0.00) to 27.66 cm⁻¹ (x = 0.06), confirming defect-driven structural modifications and a transition to cubic symmetry. XPS analysis confirmed the successful incorporation of BiGdKZrO₃ by identifying oxidation states and chemical bonding. The UV–Vis spectra showed a band gap between 3.34 and 3.41 eV, which is caused by charge correction and band tailing caused by defects. FE-SEM and HRTEM studies showed that the grains are spread out evenly and that the lattice was significantly distorted at x = 0.04. The SAED patterns changed to dispersed rings, which confirmed the phase transition and the development of defects. Electrical impedance spectroscopy showed enhanced AC conductivity with increasing frequency and temperature (410–500 °C, 1 Hz–1 MHz). Complex permittivity (εʹ) increased from 215 (x = 0.00) to 287 (x = 0.06) at 1 MHz, while AC conductivity at 500 °C rose from 1.2 × 10⁻⁵ S/cm (x = 0.00) to 3.8 × 10⁻⁵ S/cm (x = 0.06), confirming enhanced charge transport. The real and imaginary permittivity exhibited frequency-dependent relaxation behavior, while electrical modulus analysis indicated bulk and grain boundary contributions. At higher dopant concentrations, the materials showed negative permittivity, which may be attributed to flexoelectric effects and dipolar polarization.