ABSTRACT

NON-TECHNICAL DESCRIPTION: Coupling between electrical and mechanical impulses underlies the basic behavior of many sensors and actuators. Classical piezoelectric materials are based on a linear correlation between the developed charges and applied stress (sensor applications) or strain developed under an applied electric field (actuator applications). With the drive towards miniaturization for micro- and nano-electromechanical systems (MEMS and NEMS), piezoelectric materials have received additional interest because piezoelectric actuation and sensing at the nanoscale can be conducted with much higher actuation power densities than with electrostatic and magnetoelectric approaches. This finding is in contrast to classical piezoelectric materials that offer only a limited strain range, and actuating device structures offer only limited scalability below the micron level. This work aims to take advantage of novel physical phenomena, i.e. flexoelectricity (coupling between strain gradients and developed charge), emergent on the nanoscale, to develop novel electromechanical materials systems scalable to nanometer sizes, while allowing for large strains. The electromechanical response scales inversely with the dimensions of flexoelectric composites (and therefore miniaturized samples), a trend opposite to what is observed in currently-available bulk single-crystal or ceramic piezoelectrics. The response of flexoelectric composites cannot be thermally or electrically degraded, and Pb-free compositions should offer much larger electromechanical response than current Pb-based piezoelectric materials. Therefore, flexoelectric nano-composites may enable a wider range of miniaturized applications and an environmentally-safe alternative to current bulk sensors and actuators.

TECHNICAL DETAILS: This research aims to achieve fundamental understanding of flexoelectricity as a contributor to the electromechanical response of all dielectrics, and to harness it as a new transduction approach for micro- and nano-systems. The combination of precise nano-manufacturing methods with rigorous dielectric and (micro- and macro-scale) piezoelectric characterization, in addition to exhaustive microstructural characterization will provide a major insight into the multiscale science of flexoelectric composites. This research aims to establish theoretical and experimental limits for high electromechanical response through flexoelectricity in micro- and nano-meter patterned dielectrics, and correlate dielectric (microstructural) and flexoelectric (geometric) scaling effects to understand their co-regulation of the effective piezoelectric response in flexoelectric patterned dielectrics. A new understanding of flexoelectricity facilitates the required departure from lead-containing crystals, which remain the cornerstone of ceramic sensors and actuators. Flexoelectric coupling provides a potentially transformative companion to the conventional approaches of solid-solution engineering once the relationships between strain gradients, nanostructure, and phase transitions are well understood. An integral part of this project is the recruitment and retention of women in science and engineering. This objective is achieved through hands-on workshops (focused on smart materials) targeted to groups of girls in grades 5-12, as well as mentorship, research and education activities targeted at graduate and undergraduate students in cutting-edge scientific and technological fields.

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