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

Abstract

A new polar noncentrosymmetric material, Li2Ti(IO3)(6), has been synthesized and characterized. The material is built up from a TiO6 octahedron that is linked to six IO3 polyhedra. These polyhedral groups are separated by Li+ cations. The Ti4+ and I5+ cations are in asymmetric polar coordination environments attributable to second-order Jahn-Teller effects. The distortion associated with the Ti4+ cation is negligible, since the TiO6 octahedra are completely surrounded by IO3 polyhedra. The I5+ cation is in a highly polar asymmetric coordination environment attributable to its stereoactive (one pair, which was qualitatively described by pseudopotential calculations of the electron localization function. The macroscopic polarity of Li2Ti(IO3)(6) may be attributed to parallel alignment of the stereoactive tone pairs on the I5+ 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 I5+ is not switchable.