Origin of the strong optical nonlinearity of tellurium oxide-based compounds: The specific case of BaTe2O6

This paper is a contribution to the understanding of the crystal chemistry origin of the strong nonlinear optical properties of tellurium oxide-based compounds. The particular case of the BaTe2O6 (BaTeIVTeVIO6) phase has been investigated. The structure refinement using single crystal X-ray diffraction confirms that the TeIV atom is located in an unclassical TeO5 environment with one exceptionally short Te-O bond (1.82 Å) and four long ones (2.12 Å). The vibrational analysis points out that in this environment, from the spectrochemical point of view, the short bond is at the origin of a quasi-isolated TeIVO2+ molecular ion whereas the four longer bonds traduce weak interactions. Relationships have been established between the TeIV-O bond lengths and the χ(3) susceptibility. The four long bonds, belonging practically to the xz-plane and involving the TeIV d-orbitals contribution, are at the origin of the high χ(3)xxxx and χ(3)zzzz values (30.0 and 44.3 × 10−13 esu respectively). The short Te-O bond, directed along the y-direction, is responsible for the lower χ(3)yyyy value (3.2 × 10−13 esu). This study is the first obvious confirmation for a real crystal lattice of the high superiority of the nonlinear polarizability of the weak intermolecular Te-O bonds over that of the strong molecular Te-O ones.