Optomechanical Mapping of Ferroelectric Domains and the Piezo‐Photovoltaic Effect in Ba‐ and Ni‐Doped (K_0.5Na_0.5)NbO₃

Abstract

The piezo‐photovoltaic effect has been recently proposed as an analogy of the flexo‐photovoltaic effect in noncentrosymmetric ferroelectrics that are also piezoelectric in nature. It has been demonstrated to boost the photovoltaic performance of ferroelectrics under applied uniaxial mechanical loads. The impact of the piezo‐photovoltaic effect on ferroelectric domains, however, has not yet been studied. In this context, a nanoscale insight into mechanical as well as optomechanical control of domains in a novel bandgap‐engineered ferroelectric, namely—KNBNNO ((K0.5Na0.5)NbO3–2 mol% Ba(Ni0.5Nb0.5)O3−δ), is provided. It is found that the applied mechanical force of 1 μN (pressure: 0.25 GPa) using a scanning probe tip evinces a 67% amplification in piezoresponse in the material, and on removing mechanical load, the material retains 33% higher piezoresponse than the pristine state. Mechanically induced property changes in the material are found to be strongly influenced by light illumination. Applied mechanical stress due to an atomic force microscopy (AFM) tip is highly nonuniform and can induce additional polarization via the flexoelectric effect which further enhances the photovoltaic charge screening.

Optical Memory, Switching, and Neuromorphic Functionality in Metal Halide Perovskite Materials and Devices

“…In terms of light-triggered initiation of synaptic elements, above-bandgap photons can generally produce a photoconductance response, [86] especially in weakly screened semiconductors without large excitonic effects (but also in many cases within excitonic semiconductors [87] ), that can be modulated by a number of mechanisms. Light energy can also induce structural changes, [88,89] lattice relaxation, [90] diffusion of elements/ions and vacancies [91] and even reversible chemical reaction(s). [92] In terms of light-mediated read-out of synaptic elements, the two primary handles are the material's optical complex refractive index or dielectric constant (which can be detected via how light is absorbed, transmitted, and/or reflected by the medium) and/or photons emitted by the material, both of which can be modulated by various stimuli through several mechanisms.…”

Neuromorphic functionality of ferroelectric domain walls

“…Of specific interest is the dynamic range of changes in resistivity, which can span several orders of magnitude for domain walls [33,36,52,102,106,109]. This could be further improved through the introduction of optically controlled screening in ferroelectrics [120][121][122][123][124][125][126] or optically driven phase changes [127,128], giving rise to optoelectronic neuromorphic elements. Besides, the presence of ferroic or polar order in novel materials, e.g.…”

Filterless Visible‐Range Color Sensing and Wavelength‐Selective Photodetection Based on Barium/Nickel Codoped Bandgap‐Engineered Potassium Sodium Niobate Ferroelectric Ceramics

“…The rationale of studying the specific composition in this work is that the family of Ba-and Ni-codoped (K,Na)NbO 3 (referred to as KNBNNO, KNN-BNN, or KNN-BNNO) has been systematically and thoroughly optimized from several chemical and physical aspects in our previous works. [13][14][15][18][19][20][21][22][23][24][25][26][27] Thus, it is much better known than other bandgap-engineered counterparts. In brief, two approaches could achieve to reduce the bandgap and retain reasonable ferroelectricity of the widely researched parental composition, (K,Na)NbO 3 , simultaneously.…”