47345-AC10
Energy Conversion and Power Generation in New Non-Pb Based Piezoelectric Oxide Materials: Synthesis, Characterization, and Structure-Property Relationships
During the past year we have synthesized and characterized a variety of new materials, some of which exhibit piezoelectric behavior. Piezoelectric materials have the unique ability to convert mechanical energy to electrical energy as well as electrical energy to mechanical energy. These ‘inverse’ phenomena have been termed the direct and converse piezoelectric effect respectively. Not all materials, however, are piezoelectric. For piezoelectric behavior to occur strict symmetry requirements must be met. The material in question must be crystallographically non-centrosymmetric and ideally polar, i.e. exhibiting a macroscopic dipole moment. The question is – how does one synthesize a new polar non-centrosymmetric material? We have developed a strategy whereby the incidence of polarity is increased to nearly 50% in any new oxide material. This strategy involves using cations susceptible to second-order Jahn-Teller effects, i.e. octahedrally coordinated d0 transition metals and cations with non-bonded electron pairs. The d0 metals include, Ti4+, Nb5+, W6+, etc., whereas for the lone-pair cations we are focusing on Se4+, Te4+, and Tl+. In oxides, these cations are very often observed in locally asymmetric polar coordination environments. It is our hypothesis that this local polarity is retained in the solid-state resulting in a macroscopically polar material with piezoelectric properties.
