Photoresponsive Piezoelectrics

Abstract

Most piezoelectric materials are not interactive with visible light, meaning that their band gaps are beyond the photon energies of the visible part of the light spectrum. The first narrow band gap (1.1 eV, the same as silicon) ferroelectric material based on the oxide perovskite structure has been achieved by doping Ni on the B-sites of KNbO3 and paring the Ni2+ ions with oxygen vacancies to form defect dipoles to ease the band-band transition. This band gap engineered ferroelectric material has also been proved to be piezoelectric. The Ni-doping strategy for band gap engineering has been successfully applied to other perovskite compositions. As a result, several materials with simultaneously good piezoelectricity and a visible-range band gap have been developed. Such photoresponsive piezoelectrics have potential applications in opto-electrical dual-source actuators, single-material multi-sensors and multi-source energy harvesters. This mini review focuses on the works of simultaneous tuning of piezoelectricity and band gap, which have not previously been discussed as an individual topic in existing reviews. Pioneer works on the applications of photoresponsive piezoelectrics are also presented. Since most of such materials are built on the frame of lead-free perovskite oxides, their band gap (without degrading the piezoelectricity) provides an additional benefit to environmentally friendly lead-free piezoelectrics (compared to lead-based counterparts such as PZT [Pb(Zr,Ti)O3)]. This review aims to draw the attention of piezoelectric scientists and device engineers, so that potential applications of photoresponsive piezoelectrics can be comprehensively investigated, as well as more material options that can be offered in future works.

Growth of tungsten bronze phase out of niobate perovskite phase for opto‐ferroelectric applications

“…7,8 The photo-assisted domain switching may also be used in optoelectrical dual-source actuators for remote and precise control of micromachines and medical operations. 3,9,10 Meanwhile, the intrinsic spontaneous polarization is believed to be able to assist the separation of photo-excited charge carriers. 11 This offers possibilities to develop either standalone ferroelectric solar cells free from electron-and hole-transporters or an additional layer in conventional semiconductor solar cells to help reduce the recombination and improve the photovoltaic energy conversion efficiency.…”

“…This is because most of such materials have wide optical bandgaps in the violet or ultraviolet range, making the absorption of visible-range photon energy and the associated influence of the photo-excited charge carriers on the material properties negligible. 3 However, a potentially tunable bandgap, especially when extending deep into the visible light range, will expand the application perspectives of photo-responsive ferroelectrics and piezoelectrics. For instance, previous works showed that the incident light which can excite charge carriers is able to drive or stimulate the ferroelectric domain switching.…”

“…Conventional research on ferroelectrics and piezoelectrics does not necessarily involve the interaction of microstructure (e.g., domain wall motion) and functional properties with light. This is because most of such materials have wide optical bandgaps in the violet or ultraviolet range, making the absorption of visible‐range photon energy and the associated influence of the photo‐excited charge carriers on the material properties negligible 3 …”

“…This provides opportunities to use light as a virtual gate in ferroelectric field‐effect transistors and thus to develop non‐volatile memories and artificial synapses for neuromorphic computing with writing/reading functions by light 7,8 . The photo‐assisted domain switching may also be used in optoelectrical dual‐source actuators for remote and precise control of micromachines and medical operations 3,9,10 . Meanwhile, the intrinsic spontaneous polarization is believed to be able to assist the separation of photo‐excited charge carriers 11 .…”

Light-driven motion of charged domain walls in isolated ferroelectrics

“…These interfaces move through external stimuli, typically electric field or mechanical stress, thereby yielding domains reconfiguration. Recently, however, polarization control via optical excitation has become a highly appealing topic because it entails new paradigms for technology [3][4][5][6][7][8]. Optical switching mechanisms include (piezo)photovoltaic effect [9][10][11] as well as a variety of experimentally observed phenomena based on the light control of ferroelectrics domains [12][13][14].…”