Electrooptical Kerr phenomenon and Raman spectroscopy of one lithium–niobium–silicate glass-forming system A.A. Lipovskii a , Yu. Kaganovskii b , V.G. Melehin c , D.K. Tagantsev d, * , O.V. Yanush e a St. Petersburg State Polytechnic University, Polytechnicheskaja 29, St. Petersburg, Russia b The Jack and Pearl Resnick Institute for Advanced Technology, Bar-Ilan University, Ramat Gan, Israel c A.F. Ioffe Physical-Technical Institute, Polytechnicheskaja 26, St. Petersburg, Russia d S.I. Vavilov State Optical Institute, Babushkina 36-1, St. Petersburg, Russia e St. Petersburg Technological University of Plant Polymers, I. Chernyh 4, St. Petersburg, Russia Available online 26 November 2007 Abstract Raman spectra and electrooptical Kerr coefficients of glasses belonging to one lithium–niobate–silicate glass-forming system xNb 2 O 5 Æ (66  x)SiO 2 Æ 19Li 2 O Æ 11K 2 O Æ 2B 2 O 3 Æ 2CdO are studied. It has been found that these glasses demonstrate a record value of electrooptical Kerr coefficient; the glass with x = 35 showed electrooptical Kerr coefficient equal to 266 · 10 16 m/V 2 . Using Raman spectroscopy combined with the concept of Constant Stoichiometric Groupings, a correlation of electrooptical Kerr coefficients of these glasses with the content of Li 2 O Æ Nb 2 O 5 (or 2LiNbO 3 ) groupings has been demonstrated. The hypothesis that electrooptical Kerr sen- sitivity of glasses is related to the ordered regions with composition and symmetry corresponding to some of known electrooptical crys- tals has been verified. These regions, which the authors called ‘Crystal Motifs’, are identified with the groupings found in studying Raman spectra of the glasses. Ó 2007 Elsevier B.V. All rights reserved. PACS: 42.70.C; 61.43.F; 61.43.j; 78.20.J Keywords: Raman scattering; Glasses; Non-linear optics; Oxide glasses; Medium-range order 1. Introduction Recently [1,2] the authors have suggested that enhanced (if any) electrooptical Kerr sensitivity of glasses originates in their microinhomogeneous structure, that is, in the con- centration and density fluctuations native to glasses. It is considered that if a glass demonstrates an increased elec- trooptical Kerr sensitivity, these fluctuations are the ordered regions with the structure (composition and sym- metry) corresponding to some Kerr electrooptical crystal, the regions’ size being about 2–3 coordination spheres, that is, 1–2 nm. These regions have been called the Crystal Motifs (CMs) [1]. In different designations, the very similar hypotheses are proposed by other researchers [3–7] as well. Due to small sizes of the CMs it is hardly possible to observe CMs directly, and, by now, only indirect methods have been developed (for example, Mandel’shtam–Brillou- in light scattering or small angle X-ray scattering), but they give too general information about the regions, like their average size or electron density. However, for the basic and applied reasons, it is of interest to characterize the CMs by two additional parameters: composition and sym- metry (or type of ‘crystalline’ lattice of ordered regions). In our previous work [2], it has been shown that Raman spec- troscopy can give information on the composition of typi- cal entities, which are identified with the CMs responsible for electrooptical sensitivity of glasses. The approach used is based on the presentation of vibration spectra of oxide 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.11.041 * Corresponding author. Tel.: +7 812 5601878; fax: +7 812 5609574. E-mail address: tagan@dt1386.spb.edu (D.K. Tagantsev). www.elsevier.com/locate/jnoncrysol Available online at www.sciencedirect.com Journal of Non-Crystalline Solids 354 (2008) 1245–1249