Vibrational spectra of a K0.30Na0.10Sr0.48Ba0.32Nb2O6 single crystal studied by Raman and infrared reflectivity spectroscopy

Potassium and sodium (K/Na)-modified strontium barium niobate (SBN) of the idealized formula (KxNa1-x)(0.4)(SryBa1-y)(0.8)Nb2O6 (KNSBN), with x = 0.75, y = 0.60, a Curie temperature of (200 +/- 2) degrees C, and a laser damage threshold larger than 600 MW/cm(2) at 4 pps, crystallizes with a filled tungsten bronze (TB) type structure in the tetragonal system. The lattice constants are a = (1.2488 +/- 0.0001) and c = (0.3955 +/- 0.0001) nm at room temperature. There are five formulas per unit cell. The lattice vibrational spectrum of KNSBN, which arises mainly from internal vibrations of the Nb-O octahedra and studied by Raman and infrared reflectivity spectroscopy, typifies a tetragonal TB type structure. The results shown in Figs. 1 to 6 are typical for vibrational spectra. The NbO6 clusters form the rigid Nb-O octahedra, and the rigidity of the lattice is mainly ascribed to five vibrations, as a non-degenerate symmetric Nb-O stretching vibration (v(1)), a doubly degenerate symmetric O-Nb-O stretching vibration (v(2)), a triply degenerate antisymmetric Nb-O stretching vibration (v(3)), a triply degenerate antisymmetric O-Nb-O bending vibration (v(4)), and a triply degenerate symmetric O-Nb-O bending vibration (v(5)) The KNSBN crystals as well as the SBN crystals show good structural quality and mechanical properties, and large linear electro-optical and pyroelectric coefficients. Besides, the nonlinear optical property of KNSBN is better than that of SBN.Physics, Condensed MatterSCI(E)25ARTICLE147-5921