Influence of Cr-doping on structural, morphological, optical, dielectric and magnetic properties of KNbO3 ceramics

In this work, we report on the structural, morphological, optical, dielectric and magnetic properties of undoped and Cr doped KNbO3 (KNb1-xCrxO3; x = 0.0, 0.01, 0.03 and 0.05 mol.%) synthesized at 900 °C by solid state reaction method. X-ray diffraction analysis showed the formation of single phase KNbO3 with the orthorhombic structure. Further, the Rietveld refinement analysis revealed that no impurity or secondary phase formation related to the Cr doping. The crystallite size of KNb1-xCrxO3 varies between 553 nm and 948 nm. All the characteristic Raman phonon modes of KNb1-xCrxO3 confirmed the formation of compound with the orthorhombic structure. The presence of K, Nb, O and Cr elements and a shift in binding energy of Nb and O was observed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses, respectively. Surface morphology of KNb1-xCrxO3 samples exhibit different morphologies, namely rods, cubes and micro edges. Diffuse reflectance spectra revealed that band gap of KNb1-xCrxO3 ceramics decreases with increasing Cr doping level. The photoluminescence emission peaks at ∼410-492 nm (blue) and 520 nm (green) indicate the oxygen vacancies present in the sample. A high coercivity (593 Oe) and saturation magnetization (0.021 emu g−1) is obtained for 0.03 mol.% of Cr doping. The dielectric permittivity was enhanced with the increase of Cr doping concentration in KNbO3 matrix.