Theoretical Investigation of Proton Diffusion in Dion-Jacobson Layered Perovskite RbBiNb2O7.

Perovskite materials are considered to be promising electrolyte membrane candidates for electrochemical applications owing to their excellent proton- or oxide-ion-conducting properties. RbBiNb2O7 is a double-layered Dion-Jacobson perovskite oxide, with Pmc21 symmetry. In this study, the electronic structure and proton-diffusion properties of bulk RbBiNb2O7 were systematically investigated using first-principles calculations. The unique layered crystal structure of RbBiNb2O7 plays a crucial role in proton storage and proton conductivity. Different proton-diffusion steps in RbBiNb2O7 were considered, and the activation energies of the relevant diffusion steps were evaluated using the climbing image-nudged elastic band (CI-NEB) technique. The proton diffusion in RbBiNb2O7 presents a two-dimensional layered characteristic in the a-b plane, owing to its layered crystalline nature. According to the transition state calculations, our results show that the bulk RbBiNb2O7 exhibits good proton-transport behavior in the a-b plane, which is better than many perovskite oxides, such as CaTiO3, CaZrO3, and SrZrO3. The proton diffusion in the Rb-O and Nb-O layers is isolated by a higher energy barrier of 0.86 eV. The strong octahedral tilting in RbBiNb2O7 would promote proton transport. Our study reveals the microscopic mechanisms of proton conductivity in Dion-Jacobson structured RbBiNb2O7, and provides theoretical evidence for its potential application as an electrolyte in solid oxide fuel cells (SOFCs).

Mechanism of Single-Photon Upconversion Photoluminescence in All-Inorganic Perovskite Nanocrystals: The Role of Self-Trapped Excitons.

The efficient single-photon upconversion photoluminescence (UCPL) feature of lead halide perovskite semiconductors makes it promising for developing laser cooling devices. This is an attractive potential application, but the underlying physics still remains unclear so far. By using the all-inorganic CsPbX3 (X = Br, I) nanocrystal samples, this phenomenon was investigated by photoluminescence (PL) and time-resolved PL under different temperatures and various excitation conditions. A broad emission band located at the low-energy side of the free exciton (FE) peak was detected and deduced to be from the self-trapped exciton (STE). The lifetime of STE emission was found to be 171 ns at 10 K, much longer than that of FE. The UCPL phenomenon was then attributed to thermal activation of transformation from STEs to FEs, and the energy barrier was derived to be 103.7 meV for CsPbBr3 and 45.2 meV for CsPb(Br/I)3, respectively. The transformation also can be seen from the fluorescence decay processes.

Tailoring the surface of ZnO nanorods into corrugated nanorods via a selective chemical etch method.

Using the chemical vapour deposition method, we successfully converted smooth ZnO nanorods (NRs) into corrugated NRs by simply increasing the reaction time. The surface morphology and crystallographic structure of the corrugated NRs were investigated. The corrugated NRs were decorated by alternant [Formula: see text] and [Formula: see text] planes at the exposed side surfaces while the conventional [Formula: see text] planes disappeared. No twinning boundaries were found in the periodically corrugated structures, indicating that they were type II corrugated NRs. Further investigation told us that they were selectively etched. We introduced a hydrothermal method to synthesize the smooth ZnO NRs and then etched them in a tube furnace at 950 °C with a flow of carbon monoxide. By separating the growth stage and the selective etching stage, we explicitly demonstrated a successfully selective etching effect on ZnO NRs with a carbon monoxide reducing atmosphere for the first time. An etching mechanism based on the selective reaction between carbon monoxide and the different exposed surfaces was proposed. Our results will improve the understanding of the growth mechanism on coarse or corrugated NRs and provide a new strategy for the application of surface controlled nanostructured materials.