The influence of composition on optical properties of ferroelectric potassium lithium niobate single crystals

Homogeneous crack-free Potassium Lithium Niobate (KLN) single crystals with different Li content were grown up by the TSSG technique. Lattice vibration spectra of these samples were investigated using Raman spectroscopy. The results showed that characteristic Raman spectra of the [NbO6]7−[NbO6]7− octahedral ions were strikingly influenced by the Li ions. Thus, the symmetric bend vibration mode ν5 of the KLN sample with higher Li content was split into three Raman peaks, while the sample with lower Li content displayed a single peak, supporting that the bend vibration modes of the [NbO6]7−[NbO6]7− octahedrons were obviously perturbed by Li ions occupying C-sites. Enhanced Raman peak intensities of the KLN sample post-annealed at 900 °C for 24 h evidenced that content of defects in KLN crystal might be reduced. The transmittance spectra showed that the crystal with higher Li content had better transmittance intensity.