Na_（1－x）Zr（2－x）Nb_xP_3O_（12）系列化合物的水热晶化研究

采用水热晶化反应，制备出传统需要高温固相反应合成的掺杂ＮＡＳＩＣＯＮ化合物Ｎａ（１－ｘ）Ｚｒ（２－ｘ）ＮｂｘＰ３Ｏ１２（０＜ｘ＜１），并应用ＸＲＤ、ＩＲ方法对产物的晶体结构进行了研究，表明水热晶化产物是纯的物相并具有与ＮａＺｒ２Ｐ３Ｏ１２相同的结构．固体３１ＰＮＭＲ研究证实Ｎｂ（５＋）部分取代了Ｚｒ（４＋）所在位置，参与骨架的组成，并统计分布于结构中．水热晶化产物与固相反应产物具有相同的离子电导性能．     

Study of transition metal oxide doped LaGaO3 as electrode materials for LSGM-based solid oxide fuel cells

Transition metal oxide doped lanthanum gallates, La_0.9Sr_0.1Ga_0.8M_0.2O₃ (where M=Co, Mn, Cr, Fe, or V), are studied as mixed ionic-electronic conductors (MIECs) for electrode applications. The electrochemical properties of these materials in air and in H₂ are characterized using impedance spectroscopy, open cell voltage measurement, and gas permeation measurement. Three single cells based on La_0.9Sr_0.1Ga_0.8 Mg_0.2O₃ (LSGM) electrolyte (1.13 to 1.65 mm thick) but with different electrode materials are studied under identical conditions to characterize the effectiveness of the lanthanum gallate-based MIECs for electrode applications. At 800 °C, a single cell using La_0.9Sr_0.1- Ga_0.8Co_0.2O₃ as the cathode and La_0.9Sr_0.1Ga_0.8Mn_0.2O₃ as the anode shows a maximum power density of 88 mW/cm², which is better than that of a cell using Pt as both electrodes (20 mW/cm²) and that of a cell using La_0.6Sr_0.4CoO₃ (LSC) as the cathode and CeO₂-Ni as the anode (61 mW/cm²) under identical conditions. The performance of LSGM-based fuel cells with MIEC electrodes may be further improved by reducing the electrolyte thickness and by optimizing the microstructures of the electrodes through processing. Received: 9 January 1998 / Accepted: 1 May 1998     

金属有机导体、半导体和超导体

本文综述了三类金属有机固体化合物的合成、结构与导电性能。这三类化合物是金属有机电荷转移盐,金属酞菁和会属卟啉络合物,以及金属有机夹层化合物。     

The surface and materials science of tin oxide

The study of tin oxide is motivated by its applications as a solid state gas sensor material, oxidation catalyst, and transparent conductor. This review describes the physical and chemical properties that make tin oxide a suitable material for these purposes. The emphasis is on surface science studies of single crystal surfaces, but selected studies on powder and polycrystalline films are also incorporated in order to provide connecting points between surface science studies with the broader field of materials science of tin oxide. The key for understanding many aspects of SnO₂ surface properties is the dual valency of Sn. The dual valency facilitates a reversible transformation of the surface composition from stoichiometric surfaces with Sn⁴⁺ surface cations into a reduced surface with Sn²⁺ surface cations depending on the oxygen chemical potential of the system. Reduction of the surface modifies the surface electronic structure by formation of Sn 5s derived surface states that lie deep within the band gap and also cause a lowering of the work function. The gas sensing mechanism appears, however, only to be indirectly influenced by the surface composition of SnO₂. Critical for triggering a gas response are not the lattice oxygen concentration but chemisorbed (or ionosorbed) oxygen and other molecules with a net electric charge. Band bending induced by charged molecules cause the increase or decrease in surface conductivity responsible for the gas response signal. In most applications tin oxide is modified by additives to either increase the charge carrier concentration by donor atoms, or to increase the gas sensitivity or the catalytic activity by metal additives. Some of the basic concepts by which additives modify the gas sensing and catalytic properties of SnO₂ are discussed and the few surface science studies of doped SnO₂ are reviewed. Epitaxial SnO₂ films may facilitate the surface science studies of doped films in the future. To this end film growth on titania, alumina, and Pt(1 1 1) is reviewed. Thin films on alumina also make promising test systems for probing gas sensing behavior. Molecular adsorption and reaction studies on SnO₂ surfaces have been hampered by the challenges of preparing well-characterized surfaces. Nevertheless some experimental and theoretical studies have been performed and are reviewed. Of particular interest in these studies was the influence of the surface composition on its chemical properties. Finally, the variety of recently synthesized tin oxide nanoscopic materials is summarized.     

B-site substitutions in LaNb1−xMxO4−δ materials in the search for potential proton conductors (M=Ga, Ge, Si, B, Ti, Zr, P, Al)

The solid solubilities of potential B-site dopants in LaNb_1-xM_xO_4−δ, materials, M=Ga, Ge, Si, Al, B, P, Zr or Ti, have been investigated in the search for possible novel proton conductors. In general, the solubility levels of these cations were found to be very low (x≤0.03). At the maximum value x=0.03, only compositions containing Ti, Ge, Ga and Si appeared pure at the limit of resolution of XRD. The literature phase diagram, La₂O₃-Nb₂O₅-ZrO₂, has been re-analysed for compositions of low Zr-content around the composition LaNbO₄. The electrical properties of phase pure Ti-doped compositions have been studied. Higher bulk and total conductivities were observed in wet than dry conditions, suggesting a significant protonic contribution to total conductivity. In wet conditions, the activation energy for bulk conductivity of LaNb_0.98Ti_0.02O_4-δ was found to be much higher than that of an A-site, Sr-doped material, Sr_0.02La_0.98NbO_4-δ, of similar acceptor dopant concentration. The Sr-doped composition offered higher conductivities than the Ti-doped composition up to approximately 900°C.     

Structural and Physical Properties of New Conducting Cation Radical Salts with Te-Based Counteranions, Tetraiodotellurate(II) and Hexaiododitellurate(II)

This article reports preparation, structure, and conducting property of several cation radical salts of organic donors tetramethyltetrathiafulvalene (TMTTF), ethylenedithiotetrathiafulvalene (EDT-TTF), bis(ethylenedithio)tetrathiafulvalene (ET), bis(ethylenedithio)tetraselenafulvalene (BETS) and hexamethylenetetraselenafulvalene (HMTSF) with two novel planar Te-based dianions, TeI₄²⁻ and Te₂I₆²⁻. (ET)₅Te₂I₆ 1 and (BETS)₅Te₂I₆ 2 are isostructural. In these Te₂I₆²⁻ salts, intermolecular short I···I contacts form a supramolecular corrugated anion sheet. Donor arrangement is similar to the θ-type. With lowering temperature, the resistivity of 1 shows a gradual increase followed by a sharp upturn at 110 K. 2 is metallic down to 120 K and shows a gradual increase of the resistivity followed by a clear transition to an insulating state around 60 K. Crystal structure of (ET)₄TeI₄ 3 is based on the “herring bone” arrangement of ET molecules similar to the α-type. 3 shows a semiconductive behavior around room temperature followed by a transition to an insulating state at 210 K. (EDT-TTF)₄TeI₄ 4, a semiconductor, exhibits a unique two-dimensional arrangement of dimerized EDT-TTF molecules.     

导体栅的静电屏蔽作用

采用保角变换的方法 ,计算了导体栅作屏蔽罩时的场强分布 ,所得结果表明导体栅具有很好的静电屏蔽作用     

Estimation of the protonic concentration and mobility in Ba(Zr0.81Yb0.15Zn0.04)O3−δ ceramic

Rare earth doped BaZrO₃ is one of most promising proton conducting oxides as it has high proton conductivity and sound chemical stability. Sintering aids such as ZnO, however, should be incorporated in order to improve poor sinterability. In this study, the effects of adding ZnO on proton conductivity of Yb-doped BaZrO₃ (BZYb) were investigated. From the electrical conductivities measured under various water vapor pressures, concentration and mobility of the proton were obtained. Proton mobility of BZYb with ZnO (BZYb-Zn) was smaller than that of BZYb while hydration enthalpy of BZYb-Zn was more negative than that of BZYb.     

All solid state ion-conducting cesium source for atomic clocks

Cesium containing glass with solid metal electrodes was used as a Cs atom source in a high vacuum system. A silver anode provides an injection source of highly mobile ions which sweep Cs to the cathode surface, from which they evaporate into the vacuum. Cathode metallization with finger patterns was used leaving bare glass for Cs evaporation. Laser absorption measurements show Cs vapor generation synchronous with an applied DC voltage.     

Control of mixed protonic and electronic conductivity by mixing rare-earth ortho-borates

In order to develop mixed protonic and electronic conductors, we proposed a novel concept for material design that enables to control partial conductivities by fabricating solid solutions of protonic and electronic conductors. In this work, Sr-doped LaBO₃ and Sr-doped CeBO₃ were chosen as model compounds conducting protons and electron holes, respectively. Solid solutions of the above borates, Sr-doped La_1 − xCe_xBO₃, were prepared, and their electrical conductivities were investigated in 8.5 × 10²-4.2 × 10³ Pa of p(H₂O) and 1.0 × 10-1.0 × 10⁵ Pa of p(H₂) at 1073 K. From the experimental results of the gas partial pressure dependences of the conductivities, major charge carrier species were identified as a function of x. It was found that proton was the major charge carrier when x < 0.2 while the contribution of the electron hole conduction became remarkable as x increased above 0.2. The contribution of the electron hole conduction can be interpreted by the percolation model.