Structure composition correlation in KNN-BT ceramics - An X-ray diffraction and Raman spectroscopic investigation

Lead free (1 - x)K0.5Na0.5NbO3-(x)BaTiO3 ceramics were synthesized by solid state reaction. The influence of the addition of BaTiO3 on the phase and crystalline symmetry of the KNN-based ceramics was investigated. X-ray analysis confirmed that the addition of BaTiO3 results in the change of structure from orthorhombic towards tetragonal at x = 0.04 and cubic phase above x = 0.1. The tetragonality ratio increased from 1.005 at x = 0.04 to 1.022 at x = 0.08 and then decreased. Raman spectra demonstrated a variety of changes with BT addition, mainly classified as lattice translations involving motions of the alkaline cations and internal modes of NbO6 octahedra. The symmetric stretching mode nu(1) shifted to a higher wavenumber as the concentration of BT is increased, because the incorporation of BaTiO3 in the perovskite unit distorted the O-Nb-O bond angles. A linear relationship was observed in tetragonality ratio calculated by XRD and Raman shifts. This correlation between XRD and Raman spectroscopy results can be used to assess the crystalline symmetry in KNN-modified systems. (C) 2013 Elsevier B.V. All rights reserved