Forced electrostriction by constraining polarization switching enhances the electromechanical strain properties of incipient piezoceramics

Recently developed lead-free incipient piezoceramics are promising candidates for off-resonance actuator applications due to their exceptionally large electromechanical strains. Their commercialization currently faces three critical challenges: the high driving electric field required for delivering the potentially large strains; large strain hysteresis, which is inappropriate for precision devices; and relatively high temperature dependencies. We propose that instead of utilizing incipient piezoelectric strains, harnessing the maximum possible electrostriction would provide a highly effective way to resolve all these challenges. This concept was experimentally demonstrated using textured 0.97Bi1/2(Na0.78K0.22)1/2TiO3-0.03BiAlO3 as an exemplary incipient piezoceramic, whereby texturing was achieved using a reactive templated grain-growth technique. The manufactured textured ceramic is characterized by Smax/Emax of 995 pm V−1 and an electrostrictive coefficient, Q33, of 0.049 m4 C−2. Both these parameters are as large as those of single crystals. The current work presents a significant advancement in the field of lead-free ceramics and can guide future efforts in this direction. In addition, the concept presented here can be easily transferred to other disciplines involving the design of functional properties of various materials. Restricting how ceramics grow using electric fields and crystal templates yields safer alternatives to conventional piezoelectric materials. Bismuth-based ’incipient‘ piezoelectrics –named for the stable domain structures that emerge in polarizing electric fields – are promising lead-free ceramic actuators. Reducing the footprint of incipient states can considerably improve the stability and displacement characteristics of these piezoceramics. Wook Jo from the Ulsan National Institute of Science and Technology in Korea and colleagues have now achieved this by exerting tight control over the domain nucleation process. They employed a templated grain growth technique to produce ferroelectric ceramics that had highly oriented charge distributions after heating. Aligning the ceramic's polarization direction perpendicular to a field used for piezoelectric expansion or contraction minimized domain reorientations and maximized the available electromechanical area. A novel way of exploiting incipient piezoelectric strain of lead-free piezoceramics is introduced by demonstrating that a crystallographically constrained polarization allows a maximum use of potentially available electrostriction in materials. This approach enables the incipient piezoceramics to overcome their inherent weaknesses hindering their commercialization.