Structural, dielectric properties and Raman scattering of Li-modified K0.5Na0.5NbO3 (KNN) lead-free ceramics

The Perovskite structured lead-free ceramics (K0.5-xLixNa0.5) NbO3 (KNN: xLi3+) composition was synthesized by the conventional solid-state reaction method. The single crystallized orthorhombic phase structure at room temperature and the microstructural properties of the samples were studied by XRD and SEM techniques. Powder XRD analysis manifested that the shifting of phase from orthorhombic to tetragonal occurs with the increase of Li content (x = 0.04) with the sample. SEM technique confirmed that Li has a remarkable influence on the microstructure of the sintered materials promoting homogeneous, dense, and increased grain sizes. The dielectric measurements confirmed that the phase transformations occur from the orthorhombic to tetragonal at (To-t 201 degrees C) and tetragonal to cubic - paraelectric at (Tt-c - 462 degrees C) for x = 0.04 at 1 MHz frequency. It was observed that To-t decreases and Tt-c increases with the increase of Li content (x = 0.00 to -0.04) in the KNN matrix at 1 MHz frequency. The doping and rise of Li with the ceramics increases the presence of LiNbO3 and affects sufficiently the distortion of NbO6 octahedron in the perovskite structure of the KNN system and hence Tt-c of the ceramic increases. Three Raman intensity peaks of the ceramics with x = 0.04 confirmed at v5 - 267 cm-1, v1 621 cm- 1, and v1 + v5 - 879 cm-1 respectively, which are related to the internal modes of NbO6 octahedron. The almost linear peak at 879 cm-1 confirms the phase change from orthorhombic to tetragonal.