Professor Paolo G. Radaelli OSI

Abstract:

Molecular piezoelectrics are a potentially disruptive technology, enabling a new generation of self-powered electronics that are flexible, high performing, and inherently low in toxicity. Although significant efforts have been made toward understanding their structural design by targeted manipulation of phase transition behavior, the resulting achievable piezoresponse has remained limited. In this work, we use a low-symmetry, zero-dimensional (0D) inorganic framework alongside a carefully selected ‘quasi-spherical’ organic cation to manipulate organic–inorganic interactions and thus form the hybrid, piezoelectric material [(CH3)3NCH2I]3Bi2I9. Using variable–temperature single crystal X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy, we demonstrate that this material simultaneously exhibits an order–disorder and displacive symmetry-breaking phase transition. This phase transition is mediated by halogen bonding between the organic and inorganic frameworks and results in a large piezoelectric response, d 33 = 161.5 pm/V. This value represents a 4-fold improvement on previously reported halobismuthate piezoelectrics and is comparable to those of commercial inorganic piezoelectrics, thus offering a new pathway toward low-cost, low-toxicity mechanical energy harvesting and actuating devices.

Abstract:

Ultrafast switching of ferroic phases is an active research area with technological potential. Yet, some key challenges remain, ranging from limited speeds in ferromagnets to intrinsic volatility of switched domains owing to depolarizing fields in ferroelectrics. Unlike these ferroic systems, ferroaxial materials host bistable states that preserve spatial-inversion and time-reversal symmetry and are therefore immune to depolarizing fields but also difficult to manipulate with conventional methods. We demonstrate photo-induced switching of ferroaxial order by engineering an effective axial field composed of circularly driven terahertz phonon modes. A switched ferroaxial domain remains stable for many hours and can be reversed back with a second terahertz pulse of opposite helicity. The effects demonstrated in this work may lead to the development of a robust platform for ultrafast information storage.