Regulating the surface of nanoceria and its applications in heterogeneous catalysis

Ceria (CeO₂) as a support, additive, and active component for heterogeneous catalysis has been demonstrated to have great catalytic performance, which includes excellent thermal structural stability, catalytic efficiency, and chemoselectivity. Understanding the surface properties of CeO₂ and the chemical reactions occurred on the corresponding interfaces is of great importance in the rational design of heterogeneous catalysts for various reactions. In general, the reversible Ce³⁺/Ce⁴⁺ redox pair and the surface acid-base properties contribute to the superior intrinsic catalytic capability of CeO₂, and hence yield enhanced catalytic phenomenon in many reactions. Particularly, nanostructured CeO₂ is characterized by a large number of surface-bound defects, which are primarily oxygen vacancies, as the surface active catalytic sites. Many efforts have therefore been made to control the surface defects and properties of CeO₂ by various synthetic strategies and post-treatments. The present review provides a comprehensive overview of recent progress in regulating the surface structure and composition of CeO₂ and its applications in catalysis.     

多铁性钙钛矿薄膜的氧空位调控研究进展

精确调控ABO_3钙钛矿结构中氧空位的位置与浓度已被证明可调控多铁性薄膜的不同物理性质,包括输运特性、光学特性和多铁性质等.本文回顾了多种典型的多铁性材料,从氧空位形成机理、氧八面体结构、应变-氧空位关系和具体物性调控效应(多铁、超导和电化学性能)等角度介绍了该体系中氧空位调控效应.同时依托氧空位调控的最新研究进展,尤其是对氧空位调控单相材料多铁性质方面工作的分析,为探索新型磁电功能性材料与器件提供了重要参考.     

单根SnO_2纳米线器件的电输运性能及其机理研究

为探究常态环境下氧空位对单根SnO_2纳米线电输运性能的影响,采用化学气相沉积法合成了SnO_2纳米线,通过光刻微加工技术构筑了Au/单根SnO_2纳米线/Au二端纳米器件.将单根SnO_2纳米器件进行氢化处理,测试其在空气与真空中的伏安特性曲线,发现单根SnO_2纳米线在空气和真空环境中呈现异常不同的电输运特性:在空气中,加偏压注入电子会使通过纳米器件的电流减小,Au电极与SnO_2纳米线之间的接触势垒增大;抽真空后,在偏压的影响下,通过纳米器件的电流增大,Au/SnO_2交界面的接触方式由肖特基接触转变成欧姆接触.实验分析表明,影响单根SnO_2纳米线电输运特性行为的因素与纳米线表面的氧原子吸附与脱吸附所引起的氧空位浓度的变化有关.为进一步分析氧空位浓度变化的作用,利用第一性原理计算方法计算了氧空位浓度对SnO_2纳米线电输运性能的影响,通过分析体系的能带结构、态密度及Au/SnO_2接触界面的I-V曲线和透射谱,发现随着氧空位浓度的增大,SnO_2纳米线的带隙变小.同时,氧空位缺陷使Au/SnO_2接触界面处电子透射率增大,体系电输运能力变强.该研究结果将为集成纳米功能器件的设计提供一种新思路.     

Effect of lattice defects in divalent lattices by incorporating trivalent ions in biominerals: An EPR study of Cr(III) in zinc(II) potassium phosphate hexahydrate

In order to understand the effect of charge compensating vacancies on the number, orientation and magnitude of D‐tensors, single crystal EPR measurements have been carried out with Cr(III) in zinc(II) potassium phosphate hexahydrate at room temperature. During crystal rotations, a maximum of 6/7 resonance lines or a minimum of 2 is noticed. Crystal rotations done in the three orthogonal planes have yielded spin Hamiltonian parameters for one site with: g_xx=1.969, g_yy= 1.995, g_zz= 2.107; D_xx= 66.2 mT; D_yy= 91.7 mT, and D_zz=‐157.9 mT. The powder EPR spectrum indicates a very broad line at g = 8, without any extra resonances from 0 to 650 mT both at room temperature and 77 K. The reason may be that due to large zero field splitting, the resonance at g = 2 is shifted to g = 8 position and the other resonances are below 0 or above 650 mT. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Discovery of a novel visible-light-active photodetector based on bismuth ferrite: constructing and optimizing the Cr-doped-BiFeO3/NiO thin film heterostructure

Bismuth ferrite (BFO) with narrow bandgap (<2.70 eV) is an uprising star in the application of optoelectronic conversion in visible (Vis) region. Fe-site doping by transition metals is a recognized strategy to reduce leakage current in order to create more qualified BFO-based optoelectronic devices. We aim to constitute the heterostructure of BiFe_1-xCr_xO₃ (BFCO) coupling to hole-transporter NiO, serving as Vis-active photodetector with superior photoresponse speed. The influence of Cr doping ratio on BFCO is systematically investigated, indicating that doping Cr can effectively restrain not only the reduction of Fe³⁺ state but also the generation of oxygen vacancies. Moreover, by taking advantage of desirable energy-band alignment, BFCO/NiO heterojunction can reach the optimized response time constants of photocurrent rising and decay, i.e., τ_r and τ_d are, respectively, lowered down to 0.23 and 0.38 ms, which are almost two order-of-magnitude lower than that of pure-BFO/NiO and also more than one order-of-magnitude lower than that of single-layer BFCO film. It confirms an overwhelming photoresponse performance over other Vis-active counterparts. Herein, we for the first time achieve the Vis photodetector based on BFCO, by virtue of functional interfacial structure of BFCO-NiO to energetically separate photogenerated electron–hole pairs as well as improve charge carrier transportation.     

Electrical Resistivity and Thermally Stimulated Current in CuIn5Se8

From electrical resistivity measurements in the range from 240 to 450 K and from optical absorption measurements the energy gap value of CuIn₅Se₈ has been found to be 1.13 eV. Thermally stimulated current and electrical measurements at high temperature performed in indium annealed samples show deep levels at 0.55 and 0.79 eV, respectively. These defects are expected to be associated with interstitial indium or indium in copper site because of the In‐rich condition.