Magnetoelectric coupling in multiferroics probed by optical second harmonic generation.

Magnetoelectric coupling, as a fundamental physical nature and with the potential to add functionality to devices while also reducing energy consumption, has been challenging to be probed in freestanding membranes or two-dimensional materials due to their instability and fragility. In this paper, we report a magnetoelectric coupling probed by optical second harmonic generation with external magnetic field, and show the manipulation of the ferroelectric and antiferromagnetic orders by the magnetic and thermal fields in BiFeO3 films epitaxially grown on the substrates and in the freestanding ones. Here we define an optical magnetoelectric-coupling constant, denoting the ability of controlling light-induced nonlinear polarization by the magnetic field, and found the magnetoelectric-coupling was suppressed by strain releasing but remain robust against thermal fluctuation for freestanding BiFeO3.

Ultrahigh energy storage in superparaelectric relaxor ferroelectrics.

Electrostatic energy storage technology based on dielectrics is fundamental to advanced electronics and high-power electrical systems. Recently, relaxor ferroelectrics characterized by nanodomains have shown great promise as dielectrics with high energy density and high efficiency. We demonstrate substantial enhancements of energy storage properties in relaxor ferroelectric films with a superparaelectric design. The nanodomains are scaled down to polar clusters of several unit cells so that polarization switching hysteresis is nearly eliminated while relatively high polarization is maintained. We achieve an ultrahigh energy density of 152 joules per cubic centimeter with markedly improved efficiency (>90% at an electric field of 3.5 megavolts per centimeter) in superparaelectric samarium-doped bismuth ferrite­barium titanate films. This superparaelectric strategy is generally applicable to optimize dielectric and other related functionalities of relaxor ferroelectrics.

Emergent Magnetic Phenomenon with Unconventional Structure in Epitaxial Manganate Thin Films.

A variety of emergent phenomena are enabled by interface engineering in the complex oxides heterostructures. While extensive attention is attracted to LaMnO3 (LMO) thin films for observing the control of functionalities at its interface with substrate, the nature of the magnetic phases in the thin film is, however, controversial. Here, it is reported that the ferromagnetism in two and five unit cells thick LMO films epitaxially deposited on (001)-SrTiO3 substrates, a ferromagnetic/ferromagnetic coupling in eight and ten unit cells ones, and a striking ferromagnetic/antiferromagnetic pinning effect with apparent positive exchange bias in 15 and 20 unit cells ones are observed. This novel phenomenon in both 15 and 20 unit cells films indicates a coexistence of three magnetic orderings in a single LMO film. The high-resolution scanning transmission electron microscopy suggests a P21/n to Pbnm symmetry transition from interface to surface, with the spatial stratification of MnO6 octahedral morphology, corresponding to different magnetic orderings. These results can shed some new lights on manipulating the functionality of oxides by interface engineering.

Direct evidence of correlation between the second harmonic generation anisotropy patterns and the polarization orientation of perovskite ferroelectric.

For ferroelectric materials, where the polar state breaks the inversion symmetry, second harmonic generation is a useful tool to prove their ferroelectric properties. However, the correlation between the anisotropy patterns and the polarization orientation of the ferroelectric domains has not been clarified yet. In this work, we systematically investigated this correlation in a typical perovskite oxide ferroelectric, Barium Titanate (BaTiO3) crystal, by second harmonic generation and the piezoresponse force microscopy technique. The evolution of polarization-dependent anisotropy patterns proves that there is a linear relationship between the rotation angle of second harmonic generation anisotropy patterns and the polarization angle of BaTiO3 single crystals. It is a direct evidence illustrating that the polarization of BaTiO3 crystal can be qualitatively identified in 0°-180° by second harmonic generation technology. This work gives a glance at improving a nonintrusive and convenient method to identify the polarization of perovskite ferroelectric materials.

TiO(OH)2 - highly effective catalysts for optimizing CO2 desorption kinetics reducing CO2 capture cost: A new pathway.

The objective is to find a new pathway for significant reduction in CO2 capture energy consumption. Specifically, nanoporous TiO(OH)2 was used to realize the objective, which was desired as a catalyst to significantly accelerate the decomposition of aqueous NaHCO3, essentially CO2 desorption - the key step of Na2CO3/NaHCO3 based CO2 capture technologies from overall CO2 energy consumption perspective. Effects of several important factors on TiO(OH)2-catalyzed NaHCO3 decomposition were investigated. The quantity of CO2 generated from 0.238 mol/L NaHCO3 at 65 °C with catalyst is ~800% of that generated without the presence of catalyst. When a 12 W vacuum pump was used for carrying the generated CO2 out of reactor, the total amount of CO2 released was improved by ~2,500% under the given experimental conditions. No significant decrease in the catalytic effect of TiO(OH)2 was observed after five cyclic CO2 activated tests. In addition, characterizations with in-situ Fourier transform infrared spectroscopy, thermal gravity analysis and Brunauer-Emmett-Teller of TiO(OH)2 indicate that TiO(OH)2 is quite stable. The discovery in this research could inspire scientists' interests in starting to focus on a new pathway instead of making huge effort or investment in designing high-capacity but expensive CO2 sorbent for developing practical or cost-effective CO2 technologies.