Abnormal phase transition in BiNbO4 powders prepared by a citrate method

Triclinic β-BiNbO₄ prepared below 750 °C and above 1040 °C (denoted as Low-β and High-β, respectively) and pure orthorhombic α-BiNbO₄ at 900 °C were successfully derived from a citrate method and the phase transition from β-BiNbO₄ to α-BiNbO₄ was first observed in BiNbO₄ powders. This phenomenon proves that the abnormal phase transition from β-BiNbO₄ to α-BiNbO₄ exists in BiNbO₄ powder system. The synthesis of Low-β powders can be attributed to the formation of the intermediate phase of Bi₅Nb₃O₁₅ by the citrate method. With increasing temperature, the Low-β phase gradually turns into α-BiNbO₄ due to the thermodynamically metastable state of Low-β. We also identified that the stress in pellet format can accelerate the phase transition from Low-β to α phase of BiNbO₄ in comparison with powder samples. It brings us new understanding of the BiNbO₄ system and also provides a simple way to obtain BiNbO₄ for microwave and photocatalytic applications.     

Highly efficient phosphorescent organic light-emitting diodes using a homoleptic iridium(III) complex as a sky-blue dopant

Homoleptic triscyclometalated iridium(III) complex Ir(dbi)₃ was used as a dopant for sky blue phosphorescent organic light-emitting diodes (PHOLEDs). Its photophysical, thermal, electrochemical properties as well as the device performances were investigated. Ir(dbi)₃ exhibited high quantum yield of 0.52 in solution at room temperature. A maximum current efficiency and external quantum efficiency (EQE) of 61.5 cd A⁻¹ and 23.1% were obtained, which are the highest ever reported for blue homoleptic iridium complexes. High efficiencies of 53.5 cd A⁻¹ and 20.1% EQE were achieved even at the luminance of 1000 cd m⁻².     

测量反应堆快中子注量率的电流型宽禁带半导体探测器设计

为解决强流混合场快中子注量率实时测量的难题,本文基于反冲质子法,以耐辐照性能强、噪声低的半绝缘型（SI）GaN半导体材料为基础,采用带石墨平衡体及聚乙烯转换靶的并联结构,设计补偿式电流型探测器的方案,有效地降低了γ射线灵敏度。利用该探测器测量了西安脉冲堆1#径向孔道内混合场的快中子注量率,其结果与已有测量结果符合较好,验证了该方案的可行性。     

ZnS微米球的制备及光催化性能研究

利用水热法在180℃条件下制备出ZnS微米球。通过X射线衍射、扫描电子显微镜、能谱、紫外-可见吸收光谱、荧光等测试手段对产物结构和形貌进行研究,结果表明该种方法制备的ZnS样品纯度较高,为球形微米结构,直径在1～3μm。并且讨论了ZnO微米哑铃的生长机理,研究了在紫外光作用下降解次甲基蓝光催化性能。     

Improving mechanical and electrical properties of oriented polymer-free multi-walled carbon nanotube paper by spraying while winding

In this study, a new method is introduced for fabricating carbon nanotube (CNT) paper, in which the solvent is sprayed on the CNT sheet while it is wound on a rotating mandrel. As the solvent evaporated, the capillary force pulls CNT closer together, resulting in a CNT paper with a high degree of alignment and a high packing density. Three batches of multi-walled CNTs with different wall thicknesses, tube diameters and lengths are utilized for synthesizing highly oriented CNT papers. It is found that CNTs with smallest diameter of 8 nm form strongest CNT paper with a tensile strength of 563 MPa and a tensile modulus of 15 GPa, while that made with CNTs of 10 nm diameter shows the highest electrical conductivity of 5.5 × 10⁴ S/m.     

A hybrid aluminum/hydrogen/air cell system

A hybrid aluminum/hydrogen/air cell system is developed to solve the parasitic hydrogen-generating problem in an alkaline aluminum/air battery. A H₂/air fuel cell is integrated into an Al/air battery so that the hydrogen generated by the parasitic reaction is utilized rather than wasted. A systematic study is conducted to investigate how the parasitic reaction and the added H₂/air cell affect the performance of the aluminum/air battery. The aluminum/air sub-cell has an open circuit voltage of 1.45 V and the hydrogen/air sub-cell of 1.05 V. The maximum power density of the entire hybrid system increases significantly by ∼20% after incorporating a H₂/air sub-cell. The system maximum power density ranges from 23 to 45 mW cm⁻² in 1–5 M NaOH electrolyte. The hybrid system is adaptable in concentrated alkaline electrolyte with significantly improved power output at no sacrifice of its overall efficiency.     

Ordered mesoporous MgO–Al2O3 composite oxides supported Ni based catalysts for CO2 reforming of CH4: Effects of basic modifier and mesopore structure

A series of ordered mesoporous MgO–Al₂O₃ composite oxides with various Mg containing were facilely synthesized via one-pot evaporation induced self-assembly strategy. These materials with advantageous structural properties and superior thermal stabilities were used as the supports of Ni based catalysts for CO₂ reforming of CH₄. These mesoporous catalysts behaved both high catalytic activities and long term stabilities toward this reaction. The effects of the mesopore structure and MgO basic modifier on catalytic performances were carefully studied. Specifically, their mesoporous frameworks could accommodate the gaseous reactants with more “accessible” Ni active centers; the “confinement effect” of the mesopores would effectively suppress the thermal sintering of the Ni nanoparticles; the modified MgO basic sites would enhance the chemisorption and activation of CO₂. Consequently, the catalytic activities and stabilities of these catalysts were greatly promoted. Therefore, the present materials were considered as promising catalyst supports for CO₂ reforming of CH₄.     

An integrated low temperature approach to highly photoactive nanocrystalline mesostructured titania

A new type of nanocrystalline mesostructured TiO₂ (NMT) predominantly in the anatase phase with a high specific surface area up to 269 m² g⁻¹ was prepared by a novel integrated nonhydrolytic sol–gel/UV-illumination technique at low temperature. During the gaseous phase photocatalytic degradation of acetone, the material exhibited excellent photoactivity, much higher than commercial Degussa P-25, which closely related to the markedly enhanced crystallization degree and the beneficial formation of surface Ti–OH groups on the NMT sample during the post UV-illumination process.     

Influence of GaInP ordering on the performance of GaInP solar cells

CuPt-type ordering with undesirable properties always occurs in GaInP at growth conditions that are very close to those leading to the highest quality material in metal organic chemical vapor deposition. In this work, highly disordered GaInP with high crystalline quality was obtained by optimizing growth conditions. Room-temperature and low-temperature photoluminescence (PL) spectra of AlGaInP/GaInP/AlGaInP double heterostructures (DHs) reveal that the band edge emission intensity is enhanced by optimizing growth temperature, V/III ratio, and reactor pressure at the expense of low energy peak originating from spatially indirect recombination due to the ordering-related defects. The DH sample with less ordering-related defects demonstrates a longer effective minority carrier lifetime, consequently, the GaInP solar cell shows a significant improvement in the performance.     

Production of carbon nanotubes by single-pulse discharge in air

The production of carbon nanotubes (CNTs) has various methods, such as arc discharge, laser ablation, chemical vapor deposition (CVD), template-directed synthesis. These methods generally require, besides catalyst particles, vacuum environment and special ambient gas to prevent carbon from high temperature oxidation. However in this paper, CNTs were successfully produced on selected locations under atmospheric environment and room temperature by micro electrodischarge method. The micro electrodischarge system was composed with transistor circuit to offer discharging time of microseconds and peak current of several ampere. The effect of peak current and discharging time on the production of CNTs was addressed. Experimental results show that the structure and quantity of CNTs is different with different processing parameters. Multi-wall CNTs with the outer diameter of 17 nm and inner diameter of 5 nm were produced using peak current of 2.5 A and discharging time of 1000 μs.