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We proposed to synthesized and characterize new non-Pb containing oxides that have piezoelectric properties. Piezoelectric materials are used in a variety of technologically important devices such as sonar, transducers, and micro-motors, since they have the ability to convert mechanical energy to electrical energy and vice-versa. A challenge to synthesize new piezoelectric materials is their strict symmetry requirements – the materials in question must be crystallographically non-centrosymmetric and, ideally polar. We have developed a methodology whereby the incidence of non-centrosymmetry is increased in any new material to nearly 50% by utilizing cations susceptible to second-order Jahn-Teller (SOJT) distortions. These cations are octahedrally coordinated d⁰ transition metals, Ti⁴⁺, Nb⁵⁺, W⁶⁺, etc., and cations with non-bonded electron pairs, Se⁴⁺, Sn²⁺, I⁵⁺, etc. Both groups of cations are in non-centrosymmetric and polar coordination environments attributable to SOJT effects.  By using these cations we have synthesized a host of new non-centrosymmetric and polar materials including A₂Ti(IO₃)₆ (A = Li or Na), RbSe₂V₃O₁₂ and TlSe₂V₃O₁₂. Each set of materials will be briefly discussed.

·         A₂Ti(IO₃)₆ (A = Li or Na): This set of materials also includes other ‘A' cations, such as K, Rb, Cs, and Tl, but only the Li and Na phases are non-centrosymmetric and polar. Using cation size arguments, coordination preferences, and bond valence concepts, we will demonstrate that it is the “A” cation that controls the macroscopic polarity of the reported materials. In addition, electronic structure calculations indicate that although Na₂Ti(IO₃)₆ is polar, macroscopic dipole moment reversibility is energetically very unfavorable, and thus, the material is not ferroelectric.

·         RbSe₂V₃O₁₂ and TlSe₂V₃O₁₂: Both of these materials are also non-centrosymmetric and polar. The materials are structurally similar to the previously reported KSe₂V₃O₁₂ and CsSe₂V₃O₁₂. We also resynthesized KSe₂V₃O₁₂ and CsSe₂V₃O₁₂. With all four compounds, second-harmonic generation, piezoelectricity, polarization, thermogravimetric, infrared, and UV-vis measurements were performed. In addition, electronic structure calculations were done. These calculations indicate Tl⁺ exhibits an inert rather than stereoactive lone pair.

These materials were synthesized and characterized by a graduate student in my laboratory, Mr. Hong Young Chang, who finished his PhD in the summer of 2009.