Vibrational Spectra of a K0.30Na0.10Sr0.48Ba0.32Nb0.2O0.6 Single Crystal Studied by Raman and Infrared Reflectivity Spectroscopy

Abstract

Potassium and sodium (K/Na)-modified strontium barium niobate (SBN) of the idealized formula (K x Na 1 x)0.4(SryBa1-y)0.8Nb2O6 (KNSBN). with x = 0.75. y = 0.60, a Curie temperature of (200 ± 2) 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 NbO 6 clusters form the rigid Nb-O octahedra, and the rigidity of the lattice is mainl 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 SRN 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,