Vibrational Spectra of a K0.30Na0.10Sr0.48Ba0.32Nb0.2O0.6 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)0.8Nb2O6(KNSBN), withx = 0.75,y = 0.60, a Curie temperature of (200 ± 2) °C, and a laser damage threshold larger than 600 MW/cm2 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 (ν1), a doubly degenerate symmetric O–Nb–O stretching vibration (ν2), a triply degenerate antisymmetric Nb–O stretching vibration (ν3), a triply degenerate antisymmetric O–Nb–O bending vibration (ν4), and a triply degenerate symmetric O–Nb–O bending vibration (ν5). 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.