Novel Piezoelectric Materials for Sonar Transducers

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Based on the recent discovery elsewhere that when thin films of hafnium oxide (HfO2) are crystallized under certain mechanical constraints they become piezoelectric, this project seeks to answer the question whether bulk materials can be prepared with the same or similar piezoelectric crystal symmetry. The search will not be restricted to simple modifications of HfO2, but will also consider binary compounds of the type AxB(1-x)O2.The project will review the known crystal structures of the candidate compounds in comparison to the piezoelectric variant of HfO2 and formulate some simple symmetry existence criteria for these structures, similar to the Goldschmidt tolerance factor for perovskites. We will attempt to fill any gaps in the literature data through synthesis and structure analysis of the compounds by solid state chemical routes.Based on the structure existence criteria derived from the survey, a strategy to identify potential piezoelectric variants, including forming solid solutions between candidate compounds and HfO2 or ZrO2. These compounds will be prepared and their structures analysed as a function of temperature. Promising compounds will be sintered and tested for ferroelectricity and piezoelectricity. The properties of any resulting piezoelectric compounds will be compared to existing materials and assessed for potential use in sonar transducers and other applications.The current worldwide search for lead-free piezoelectric materials has focussed on perovskites, this project has the potential to identify completely new non-perovskite, lead-free compounds with useful piezoelectric properties that may contribute to the existing £20 million p.a. market piezoelectric product market.