Reversible Rectification of Microscale Ferroelectric Junctions Employing Liquid Metal Electrodes.

Both ferroelectric crystals and liquid metal electrodes have attracted extensive attention for potential applications in next-generation devices and circuits. However, the interface information between ferroelectric crystals and liquid metal electrodes has so far been lacking. To better understand the optoelectronic properties of microscale ferroelectric crystals (potassium tantalate niobate, KTN) and its potential integration with liquid metal electrodes (a "printing ink" for flexible electric circuit production), microscale KTN crystals sandwiched by eutectic gallium indium (EGaIn, a liquid metal) with varied contact geometries were studied. Unlike the bulk KTN crystal junctions, the microscale KTN junctions show electrical rectifying characteristics upon light illumination, and the directionality of the rectification can be reversed by increasing the ambient temperature to a few degrees. Furthermore, a strong suppression of the current upon increasing voltage, that is, the quasi-negative differential resistance, is observed when the microscale KTN is half-enclosed by the EGaIn electrode. Our results show that trapping/detrapping of carriers affected by the crystal size and the ambient temperature is the dominant physical mechanism for these observations. These results not only facilitate a better understanding of charge transport through the microscale ferroelectric crystals but also advance the design of miniaturized hybrid devices.

Nanoheterostructures of potassium tantalate and nickel oxide for photocatalytic reduction of carbon dioxide to methanol in isopropanol.

Cubic perovskite-type and octahedral pyrochlore-type powders of potassium tantalate (KTaO3) were selectively synthesized by a single-step hydrothermal method under different concentrations of potassium hydroxide (KOH). The obtained photocatalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectra (EDS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and UV-vis absorption spectra (UV-vis). The photocatalytic activities of the KTaO3 samples for reduction of carbon dioxide to methanol under UV light irradiation were investigated. The results showed that the KOH concentration played a significant role in determining the phases of the resultant products. Compared with the cubic crystalline structure, the octahedral crystalline structure exhibited the higher photocatalytic activity. In addition, the photocatalytic activities of KTaO3 were obviously increased when a small amount of nickel oxide (NiO) was loaded as a co-catalyst. The highest rate of methanol formation was 1815 µmol/g/h when 2 wt% of NiO was loaded.

Interlayer cation exchange stabilizes polar perovskite surfaces.

Global optimization is used to study the structure of the polar KTaO3 (001) surface. It is found that cation exchange near the surface leads to the most stable structure. This mechanism is likely to be general to metal oxides containing cations of differing charge.