Abstract
In this paper, we report the synthesis of lead-free K0.5GdxVy Na0.5-xNb1-yO3 (x = 0.0, 0.02, 0.04, 0.06, y = 0.0, 0.05, 0.1, 0.15) ceramics via solid-state reaction. The X-ray diffraction (XRD) revealed the pure crystallite formation with an orthorhombic phase, whereas Gd/V co-doping induced tetragonal-orthorhombic phase coexistence and pseudo-cubic phase formation. The crystallite size decreased from 19.26 to 7.82 nm with the increase in doping. X-ray photoelectron spectroscopy (XPS) showed the existence of vanadium in + 3, + 4, and + 5 oxidation states, whereas oxygen vacancies decreased with the increase in doping concentration. The KNN ceramic samples exhibit the most prominent Raman scattering peaks around 257, 616, and 867 cm(-1) corresponding to nu(5), nu(1), (nu(1) + nu(5)) Raman active modes of NbO6 octahedra. The optical studies showed that direct bandgap energy decreased from 3.156 to 2.897 eV with increasing dopant concentration. Fourier-transform infrared spectroscopy (FTIR) revealed that Nb-O bond length decreased with the addition of dopants from 0.1713 to 0.1684 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis confirmed the coexistence of orthorhombic and tetragonal phases. The KNN ceramics exhibited enhanced dielectric constant with high T-c of 777 K and relaxor behaviour attributed to the formation of polar nanoregions and multiple phase coexistence.