Alignment of Lone Pairs in a New Polar Material: Synthesis, Characterization, and Functional Properties of Li2Ti(IO3)6

Abstract

A new polar noncentrosymmetric material, Li(2)Ti(IO(3))(6), has been synthesized and characterized. The material is built up from a TiO(6) octahedron that is linked to six IO(3) polyhedra. These polyhedral groups are separated by Li(+) cations. The Ti(4+) and I(5+) cations are in asymmetric polar coordination environments attributable to second-order Jahn-Teller effects. The distortion associated with the Ti(4+) cation is negligible, since the TiO(6) octahedra are completely surrounded by IO(3) polyhedra. The I(5+) cation is in a highly polar asymmetric coordination environment attributable to its stereoactive lone pair, which was qualitatively described by pseudopotential calculations of the electron localization function. The macroscopic polarity of Li(2)Ti(IO(3))(6) may be attributed to parallel alignment of the stereoactive lone pairs on the I(5+) cations. This parallel alignment profoundly influences the material's functional properties: second-harmonic generation, piezoelectricity, and pyroelectricity. The material is, however, not ferroelectric, as the polarization associated with I(5+) is not switchable.