Enabling nanoscale flexoelectricity at extreme temperature by tuning cation diffusion

Abstract

Any dielectric material under a strain gradient presents flexoelectricity. Here, we synthesized 0.75 sodium bismuth titanate −0.25 strontium titanate (NBT-25ST) core–shell nanoparticles via a solid-state chemical reaction directly inside a transmission electron microscope (TEM) and observed domain-like nanoregions (DLNRs) up to an extreme temperature of 800 °C. We attribute this abnormal phenomenon to a chemically induced lattice strain gradient present in the core–shell nanoparticle. The strain gradient was generated by controlling the diffusion of strontium cations. By combining electrical biasing and temperature-dependent in situ TEM with phase field simulations, we analyzed the resulting strain gradient and local polarization distribution within a single nanoparticle. The analysis confirms that a local symmetry breaking, occurring due to a strain gradient (i.e. flexoelectricity), accounts for switchable polarization beyond the conventional temperature range of existing polar materials. We demonstrate that polar nanomaterials can be obtained through flexoelectricity at extreme temperature by tuning the cation diffusion.

Influence of oxygen vacancies on core‐shell formation in solid solutions of (Na,Bi)TiO3 and SrTiO3

“…7 NBT solid solutions with ST (NBT-ST) are of particular interest for high strain ferroelectric applications. 2,4,8,9,10,11,12,13 Strains above 0.3% could be achieved. Furthermore, the polarization hysteresis loops (polarization P plotted vs. electric field E) show pinching with low remanent polarization.…”

“…Interestingly, even at temperatures around 800 K, a ferroelectric-like polarization could be induced in such a core-shell structure, which was ultimately attributed to a flexoelectric effect. 8 The problem with that theory, however, is that the literature about NBT-ST derived compositions often does not report core-shell structures 9,10,11,12,16,17,18,19,20,21,22,23,24,25,26,27 or specifically states that is non-present. 28,29 Therefore, it is of high importance to rationalize the formation and impact of core-shell structures in the respective materials.…”

“…NBT solid solutions with ST (NBT‐ST) are of particular interest for high strain ferroelectric applications 2,4,8,9,10,11,12,13 . Strains above 0.3% could be achieved.…”

“…No proof of actual anti‐ferroelectricity could be shown in these types of materials. The work by Koruza et al, 2 Liu et al, 4 and Molina‐Luna et al, 8 however, introduced an exciting hypothesis. They elucidated the existence of the core‐shell structure in NBT‐25ST and could show that the shell is ST rich while the core is rather pure NBT.…”

In Situ Transmission Electron Microscopy Analysis of Thermally Decaying Polycrystalline Platinum Nanowires

“…The chip provides a temperature accuracy of <5% and a temperature stability of <0.01 °C at 800 °C. 40 The temperature was increased by using temperature ramps of 25 to 50 °C per step, from 250 to 1100 °C with holding times of 15 min. The sizes of voids and grains as well as the diameters of nanowires were determined from the TEM images using the image processing software ImageJ.…”