Flexoelectric Domain Walls Originated from Structural Phase Transition in Epitaxial BiVO₄ Films

Abstract

Polar domain walls in centrosymmetric ferroelastics induce inhomogeneity that is the origin of advantageous multifunctionality. In particular, polar domain walls promote charge‐carrier separation and hence are promising for energy conversion applications that overcome the hurdles of the rate‐limiting step in the traditional photoelectrochemical water splitting processes. Yet, while macroscopic studies investigate the materials at the device scale, the origin of this phenomenon in general and the emergence of polar domain walls during the structural phase transition in particular has remained elusive, encumbering the development of this attractive system. Here, it is demonstrated that twin domain walls arise in centrosymmetric BiVO4 films and they exhibit localized piezoelectricity. It is also shown that during the structural phase transition from the tetragonal to monoclinic, the symmetry reduction is accompanied by an emergence of strain gradient, giving rise to flexoelectric effect and the polar domain walls. These results not only expose the emergence of polar domain walls at centrosymmetric systems by means of direct observation, but they also expand the realm of potential application of ferroelastics, especially in photoelectrochemistry and local piezoelectricity.

Piezo-Photocatalytic and Photocatalytic Bismuth Vanadate Nanorods with Antibacterial Property

“…Clear bright and dark contrasts associated with polarized ferroelectric domain structures can be seen in the phase and amplitude images. Compared to C300, C500 exhibits a contrast which is more pronounced, indicating a multidomain-like structure with a larger extent of surface polarization. ,, …”

“…Compared to C300, C500 exhibits a contrast which is more pronounced, indicating a multidomain-like structure with a larger extent of surface polarization. 13,18,19 Figure S5a displays the Kubelka−Munk absorption plot of the samples derived from their diffuse reflectance spectroscopy (DRS) spectra. The 467 nm peak undergoes a spectral redshift in the calcined samples, showing that the monoclinic scheelite system experiences a change in its electronic structure.…”

“…Defects also contribute to flexoelectricity. , Contrary to ferroelectricity, centrosymmetric nonpiezoelectric nanocrystals subjected to mechanical stress exhibit piezoelectricity due to surface atomic contribution. − Surface piezoelectricity is the category of piezoelectricity in nanosystems. Earlier studies have demonstrated that BiVO 4 has both flexoelectric and piezoelectric properties. ,, …”

“…Earlier studies have demonstrated that BiVO 4 has both flexoelectric and piezoelectric properties. 13,18,19 Having said that, this study examined the photocatalytic, piezo-photocatalytic, and piezocatalytic activities of BiVO 4 nanorods when they were subjected to light and ultrasonic vibration. We have produced monoclinic scheelite BiVO 4 nanorods using the hydrothermal technique.…”

FIB and Wedge Polishing Sample Preparation for TEM Analysis of Sol-Gel Derived Perovskite Thin Films

“…Focusing on the field of thin film ceramics, this is not so different. Methods such as grinding and polishing [13][14][15] or dimple grinding [16,17] followed by energy ion milling or focused ion beam (FIB) [18,19] are well established when working with such materials, being able to achieve thin samples suitable for atomic resolution investigations. Because the volume of interest is reduced when studying thin films (in comparisons with their bulk counterparts), more accuracy and skill are needed to prepare the sample, even more so for cross-sectional analysis compared to plane view investigations.…”