Crack-free potassium lithium niobate (KLN) single crystals of different compositions have been grown by the resistance-heating Czochralski technique. The crystal structure was studied using synchrotron radiation X-ray powder diffraction, and the crystal compositions were determined by X-ray fluorescent spectroscopy. Homogeneous and crack-free samples of about 6 x 6 x 7 mm(3) were used to study the lattice vibration spectra by Raman and infrared reflection spectroscopy. The results show a strong influence of Li ions in the C sites of the KLN crystal on the characteristic Raman and infrared reflectivity spectra of the Nb-O octahedral ions. In particular, the symmetric bend vibrational mode, nu(5), is split into three Raman peaks; the antisymmetric bend vibrational mode, nu(4), in the infrared spectrum is split into three peaks as well. The antisymmetric stretch vibrational mode, nu(3), is broadened greatly and slightly split. The crystals obtained have good quality and improved second harmonic generation properties. (C) 2002 Elsevier Science B.V. All rights reserved.