Investigation of the Structural, Microstructural and Optical Properties of Cobalt-Doped Silver Sodium Niobate Ceramics

As a replacement for lead-based ceramics, pure and cobalt-doped silver sodium niobate (ANN) perovskite ceramics Ag0.2CoxNa0.8-xNbO3 (where x = 0, 0.02, 0.04, 0.06, 0.08) were synthesized by solid-state reaction. In the present study, the effect of cobalt doping at the A-site on the structural, microstructural and optical properties of prepared ANN specimens is presented. Perovskite orthorhombic specimens were confirmed by x-ray diffraction (XRD) along with a decrease in the average crystallite size with the increase in Co doping. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX) were conducted to determine the morphology of the fabricated samples. The average grain size of the samples, as found by using ImageJ software, was in the micrometre range and showed a reduction on increasing Co concentration. The optical properties of the samples were studied by photoluminescence (PL) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) and micro-Raman spectroscopy at room temperature. PL analysis confirmed the presence of emission peaks in the visible region at wavelengths of 438 nm, 465 nm, 481 nm, 490 nm, 544 nm and 656 nm. Using UV-Vis DRS analysis, the direct band gap of the samples was calculated by drawing Tauc plots using the Kubelka-Munk equation. The results showed values of 3.21 eV for the pure ANN sample and 3.10 eV, 3.08 eV, 3.05 eV and 3.03 eV for Co-doped samples where x = 0.02, 0.04, 0.06 and 0.08, respectively. The FT-IR spectra indicated a strong and sharp absorption peak around 534 cm-1 for all the prepared samples, showing the presence of Nb-O bond stretching and Nb-O-Nb bond bending. Analysis of the recorded Raman spectra showed vibration bands of the prepared ANN samples.