Mechanoelectric effect in O<Superscript>2−</Superscript> conducting cell: Relations to phase transformations and other lattice changes in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + <Emphasis Type="Italic">x</Emphasis></Subscript>-like oxides

The origin of mechanoelectric voltage arising in an ^2?-conducting solid-state cell O₂,Pt|ZrO₂|Pt, O₂, YBCO due to the pressure applied on the YBCO sample is discussed. It is demonstrated that the mechanoelectric voltage is the sum of the electronic and ionic mechanoelectric contact potentials. The mechanoelectric contact potentials are determined by the work done by the load during an elementary ordering act or another elementary process taking place when the sample absorbs one oxygen atom. Effects related to oxygen atoms being ordered under the load, such as pressure-induced oxygen absorption, enhanced deformation, and change in the order parameter, are discovered.     

Transport properties of materials with the scheelite structure and their modification by doping

Materials with the scheelite structure exhibit mixed ionic and electronic conductivity, and are of interest as oxidation catalysts. Scheelite materials, with the general composition ABO₄ are also possible candidates for use as electrolytes or cathode materials in solid oxide fuel cells. Our work on the scheelite system, based on BiVO₄, shows that both ionic and electronic components of the conductivity can be modified by doping this material. Both A and B site doping have been investigated in the range of 5 mol% dopant concentration. The A cation was replaced by Ca²⁺ and Ce⁴⁺, and the B site by Mn⁴⁺ and Mo⁶⁺. The phase purity was verified by XRD methods. The total and partial conductivities of pure and doped BiVO₄ were investigated by use of the emf technique and ac impedance spectroscopy. Measurements were made between 550° C and 700° C and the oxygen gradient in the emf cell was established by oxygen and air gas flows with specified flow rates and oxygen partial pressure. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994.     

Bi2O3-Y2O3系高氧离子导体的离子电导和电子电导的研究

用交流电桥法研究了Bi₂O₃-Y₂O₃体系含22.5—30mol％Y₂O₃烧结试样在po₂值由1至10^-21atm范围内氧离子的电导率,实验证明该种材料的氧离子电导率比同温度下ZrO₂基固体电解质高若干倍;用这种材料作为固体电解质组成氧浓差电池,电池电动势和理论电动势的比值E/E₀等于1或接近1,说明这种材料几乎为纯氧离子导体,p型电子空穴导电性很小;用库伦滴定抽氧法测定了含Y₂O₃ 27.5mol％样品的电子导电特征氧分压,其值为lgp_e＇=(-767000/T)+655,电子导电性极小。可期望为一种新型氧离子导体材料。 关键词：     

Proton and native-ion conductivities in Y2O3 at high temperatures

The ionic conductivity of hot-pressed samples of undoped Y₂O₃ has been studied by the emf-method in atmospheres of controlled oxygen and water-vapor pressures. The variation in the ionic conductivity was studied as a function of time (7 months at 1200°C), temperature (600–1300°C), water-vapor pressure (3–1400 Pa), and oxygen pressure (10⁻¹⁰ −10⁵ Pa). The overall conductivity can be divided into contributions from electronic carriers (mainly electron holes), native ionic defects, and hydrogen defects. The transport of charged hydrogen species is dominated by migration of “free” protons. The hydrogen-ion conductivity is detectable under all conditions and becomes the dominant ionic-conductivity contribution at high water-vapor pressures and low temperatures. The ionic contributions are discussed in terms of grain-boundary and bulk transport properties. Native-ion and proton-diffusion coefficients in yttria are estimated. Equations for the emf of oxide specimens containing charged hydrogen defects have been derived.     

Function and analytical formula for nanocrystalline dye-sensitization solar cells

Based on the experimental observations that the three-phase nano-TiO₂/F:SnO₂/I^-/I^- ₃ electrolyte front contact has to have pronounced rectifying properties (reverse reaction with electrolyte suppressed) for efficient operation of the dye-sensitization solar cell and plays an active part in the generation of photoelectrochemical energy, an analytical formula is derived which allows the understanding of the relevance and involvement of a variety of kinetic and cell parameters. Essentially, the TiO₂ layer is treated as a photocathode, donating electrons to a kinetically controlled front contact, with the counter-charges being transported by the electrolyte within the pores. The formula was expanded to include photochemical kinetics of the sensitizer, for which photodegradation properties were also calculated. The branching ratio, the ratio of regeneration-rate constant of the sensitizer and of product-formation rate, turned out to be critical for long-term stability. It may have to be improved by one order of magnitude for efficient cells to reach a lifetime of 20 years. The degree of rectifying character of the nano-TiO₂/F:SnO₂/I^-/I^- ₃ electrolyte interface (electric-field-dependent charge transfer to the front contact versus recombination-rate constant with I₃ ^- distinguishes between a low-efficiency (‘dynamic’) Galvani-type solar cell (efficiency determined by photoinduced chemical potential gradients, no rectifying contact) and a more highly efficient ‘junction-type’ solar cell (separation and collection of charges additionally assisted by junction potential). Several controversial subjects are addressed. The key challenges for the improvement of such cells are discussed, especially with respect to photodegradation and to solid-state devices. Received: 18 September 2000 / Accepted: 17 January 2001 / Published online: 20 June 2001     

Ionic-electronic mixed conduction in LixV2O5

The dc conductivity of lithium vanadium bronze, Li_xV₂O₅ was measured on polycrystal prepared by solid-state reaction in the x region 0.25–0.70. Both electronic and ionic conduction was observed. The former increased with increase of lithium content and was nearly equal to the total conductivity 10^-1–10⁰ S/cm. The ionic conductivity (∽10^-4 S/cm) measured by dc four-probe technique decreased as the lithium content increased in the range 400–500°C. The apparent activation energy for ionic conduction varied from 57 kJ/mol for x of 0.25 to 82 kJ/mol for x of 0.50.     

Impedance spectroscopy of Na+ conducting zeolite ZSM-5

The electrochemical impedance of Na⁺ ion conducting zeolite Na-ZSM-5 contacted with gold electrodes is measured. Complementary impedance measurements of the same material contacted with Na⁺ ion conducting Na₂CO₃ enabled the separation of volume and electrode parts of the impedance. Both volume and electrode impedances consisted of multiple components. Possible underlying mechanisms are discussed in view of the application of zeolites as sensitive materials in solid-state ionic gas sensors.     

Determination of non-stoichiometry in n-type AgBr by the measurement of transient current in an improved dc polarization cell

In order to determine the non-stoichiometry in AgBr, the transient current in a dc polarization cell, Ag/AgBr/Pt, was studied. When electrolytic current in the cell was completely blocked, only electronic current was allowed to flow through the AgBr/Pt interface, whereas both ionic and electronic carriers were transported through the Ag/AgBr interface at transient state. The ionic current through the Ag/AgBr interface was related to the change in δ in the formula of Ag_1+δBr. The following methods were proposed to determine δ from the transient current measurement: (i) The chemical diffusion coefficient, D?, of AgBr was calculated from the analysis of the time change in transient current. The electronic conductivity, σ_e, of AgBr was obtained from the steady-state current according to Wagner's theory. From D? and σ_e, δ was calculated. (ii) The transient current at the Ag/AgBr interface was divided into ionic and electronic parts using D? determined in (i). By integrating the ionic current, the change in δ was calculated. Using an improved dc polarization cell, the complete ion-blocking at the AgBr/Pt interface was achieved. The transient current after the abrupt change in applied potential was measured at 400°C. The methods (i) and (ii) were applied to the analysis of transient current and δ⁰, δ of AgBr in equilibrium with silver metal, was determined to be (2.0±0.2) x 10^-6.     

Preparation,characterization and application of Nano CdS doped with alum composite electrolyte

A new composite electrolyte has been developed for electrochemical application and studied in details. The system contains Alum doped with nanosize cadmium sulphide (CdS) particles in the desire ratio. The structural studies were carried out by using X-ray diffraction (XRD) as well as infrared spectroscopy (IR) which affirms the composite nature of the system. The electrical properties, including ion transport studies and complex impedance spectra confirm the ionic nature of sample as well as enhancement in ionic conductivity by CdS doping. The temperature dependence measurement confirms the Arrhenius nature of sample, which is commonly observed in the ionic composite system. The dielectric constant varies with temperature, and this data is used to calculate the number of charge carrier (n/n_o) contributing to conductivity and fits well with emf variation. A cell was fabricated by sandwiching the composite between graphite and stainless steel electrodes, which shows an emf of 7 mV.     

Crystal structure analysis of Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> powder prepared by wet chemical reaction and solid-state reaction by using X-ray diffraction (XRD)

Lithium phosphate (Li₃PO₄) is one of the promising solid electrolyte materials for lithium-ion battery because of its high ionic conductivity. A crystalline form of Li₃PO₄ had been prepared by two different methods. The first method was wet chemical reaction between LiOH and H₃PO₄, and the second method was solid-state reaction between Li₂O and P₂O₅. Crystal structure of Li₃PO₄ white powder had been investigated by using an X-ray diffraction (XRD) analysis. The results show that Li₃PO₄ prepared by wet chemical reaction belongs to orthorhombic unit cell of β-Li₃PO₄ with space group Pmn2₁. Meanwhile, Li₃PO₄ powder prepared by solid-state reaction belongs to orthorhombic unit cell of γ-Li₃PO₄ with space group Pmnb and another unknown phase of Li₄P₂O₇. The impurity of Li₄P₂O₇ was due to phase transformation in solid state reaction during quenching of molten mixture from high temperature. Ionic conductivity of Li₃PO₄ prepared by solid-state reaction was ～3.10^?7 S/cm, which was higher than Li₃PO₄ prepared by wet chemical reaction ～4.10^?8 S/cm. This increasing ionic conductivity may due to mixed crystal structures that increased Li-ion mobility in Li₃PO₄.     

清洁Si(111)表面电子结构的理论研究

本文报道在原子集团模型下用CNDO-SCF方法对清洁Si(111)表面电子结构的系统研究结果:(1)计算了表面上的净电荷分布、电荷转移以及局域在各原子轨道上的电荷;发现T₃⁰,T₃⁺和T₃^-式的表面悬挂键结构较难存在;表面原子趋于形成带有分数电荷的悬挂键,而实际上这些悬挂键彼此结合成弯键;表面原子及其悬挂键上有净电荷积累,且有很强的定域性和取向性。(2)计算了原子集团模型的静 关键词：     

利用电子结构数据拟合H2分子的电子壳模型势函数参数

电子壳模型势函数在离子晶体的原子级计算机模拟中有广泛应用,其势参数主要通过拟合晶体的实验数据或电子结构数据得到.提出了通过拟合双原子分子的量子化学从头计算电子结构数据来获得该势函数的方法,并由H₂分子的电子结构数据建立了H原子间的电子壳模型势函数.此外,还应用该势函数对H⁺₂分子离子进行了计算.该势函数拟合方案更适合于共价键型的分子. 关键词： 电子壳模型势 参数拟合 共价键 2分子')" href="#">H₂分子     

Electrical characterization of highly Titania doped YSZ

The defect fluorite region of the ternary system ZrO₂-Y₂O₃-TiO₂ encompasses compositions which offer both, good electronic and oxygen ion conductivity which enable good catalytic activity for the direct oxidation of methane in a solid oxide fuel cell (SOFC). The electrical properties of compositions Y_xTi_yZr_1−(x+y)O_2−x/2 (with x=0.15, 0.2, 0.25 and y=0.15, 0.18) were characterised in order to find the composition with highest ionic and electronic conductivity. High titanium dopant concentrations (Y) of 15 and 18 atom%, near the solubility limit of Ti⁴⁺ in the fluorite structure, have been introduced to achieve a high electronic conductivity at low oxygen partial pressure. The yttrium content x has been varied between 15 and 25 atom% to find the fluorite composition with the highest ionic conductivity for each titanium level. In the pO₂-range from 0.21 to 10⁻¹³ atm the conductivity is predominantly ionic and constant over that range. The maximum ionic conductivity is 0.01 Scm⁻¹ for the compositions, which contain 15 atom% yttrium. Substantial electronic conductivity is introduced into the system at low oxygen pressures below 10⁻¹³ atm via reduction of Ti⁴⁺ ions to Ti³⁺. The maximum electronic conductivity of 0.2 Scm⁻¹ at 930 °C has been measured for a sample with 18 atom% titanium. The slope of all log(σ) vs. log(pO₂) plots follows a pO ₂ ^−1/4 -dependence. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Influence of the annealing technique on the properties of Li ion-conductive Li1.3Al0.3Ti1.7(PO4)3 films

Li_1.3Al_0.3Ti_1.7(PO₄)₃ films were comparatively prepared by rapid thermal annealing (RTA) and conventional furnace annealing(CFA). The phase identification and surface morphology of the prepared films were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical window, ionic conductivity, activation energy, and electronic conductivity were conducted by cyclic voltammetry, electrochemical impedance spectroscopy, and four-probe technique. The results show that the films prepared by RTA and CFA are homogenous and crack-free. The film prepared by RTA shows smaller grains and is denser than the one prepared by CFA. The electrochemical windows of the two films are beyond 2.4 V. The ionic conductivities of the films prepared by RTA and CFA are 2.7?×?10^?6 S cm^?1 and 1.4?×?10^?6 S cm^?1, respectively. The activation energy of the film prepared by RTA is 0.431 eV, which is slightly smaller than the one prepared by CFA. The electronic conductivity of the two films is about 10^?10 S cm^?1.     

Sm0.9Sr0.1AlO3-δ钙钛矿氧化物的固相反应合成和电学性能

用固相反应法制备了Sm_0.9Sr_0.1AlO_3-δ钙钛矿氧化物陶瓷.通过XRD,SEM和交流复阻抗谱以及氧浓差电池方法研究了样品的物相结构、微观形貌、电学性能及输运机理.结果表明,在1650℃烧结时,可以制备出单相的具有四方钙钛矿结构的氧化物Sm_0.9Sr_0.1AlO_3-δ;1650℃烧结16 h时的Sm_0.9Sr_0.1AlO_3-δ样品具有最高的相对密度和电导率,其值分别为96.7%和1.3×10^-2S/cm(900℃),比未掺杂的SmAlO₃的电导率大4个数量级左右,高温区电导活化能(T>670℃)小于低温区电导活化能(T<670℃);Sm_0.9Sr_0.1AlO_3-δ在空气气氛中是一个氧离子和电子空穴的混合导体,氧离子迁移数在0.7左右,并随温度升高逐渐增加,氧离子电导活化能(0.95eV)大于空穴电导活化能(0.84eV),900℃时氧离子电导率为9.65×10^-3S/cm. 关键词： 3')" href="#">SmAlO₃ 氧离子导电性 混合导体 活化能     

Electronic structures of imidazolium-based ionic liquids

Electronic structures of ionic liquids formed by 1-buthyl-3-alkylimidazolium ion [C_nmim]⁺ (n = 4 and 8) with various inorganic and organic anions have been investigated by ultraviolet photoemission, X-ray photoemission, inverse photoemission and soft X-ray emission spectroscopies (SXES). The comparison of the calculated density of states with the observed spectra revealed that the molecular orbital energies of these ionic liquids are significantly affected by the electrostatic Madelung potential among the ions. The SXES results clearly show that the both highest occupied and lowest unoccupied states of [C₄mim]⁺PF₆⁻ are derived from the cation as a result of strong Madelung potential. On the other hand, the SXES results show the valence electronic structures of ionic liquids with larger anion molecules, [C_nmim]⁺Tf₂N⁻ and [C_nmim]⁺OTf⁻ are contributed from the both cation and anion.     

Defect structure of lanthanum-doped calcium titanate

The defect structure of lanthanum-doped polycrystalline calcium titanate was investigated by measuring the oxygen partial pressure (10⁰–10^?18 atm.) dependence of the electrical conductivity at 1000° C and 1050°C. Two types of charge compensation were observed, namely electronic and ionic. For P₀₂ < 10^?15 atm. the carrier concentration was fixed by the amount of lanthanum (donor) added and the conductivity was found to be independent of oxygen partial pressure (electronic compensation). For higher oxygen partial pressure conditions (P₂₂ > 10^?13 atm.) the extra charge of the lanthanum was compensated by doubly ionized calcium vacancies (ionic compensation). In the ionic compensation region, a model involving a shear structure is discussed.     

菱铁矿FeCO3高压相变与性质的第一性原理研究

采用平面波赝势方法对菱铁矿FeCO₃高压下的晶体结构, 电子构型和电子结构进行了第一性原理计算研究. 研究过程中考虑了菱铁矿FeCO₃真实的反铁磁(AFM) 自旋有序态, 模拟静水压环境, 从零压逐步加压到500 GPa. 在40---50 GPa压力范围内, FeCO₃发生了从高自旋(HS) AFM态到低自旋(LS) 非磁性(NM) 态的磁性相变, 伴随着晶胞体积坍塌10.5%. FeCO₃在相变前后均是绝缘体, 但是相变后的LS-NM态的Fe²⁺ 离子的3d电子局域化程度更强, 能隙随着压力的进一步增大而逐步增大, 离化程度更高, 直到500 GPa没有发生金属绝缘体相变.     

Relationship between structural characteristics and photoluminescent properties of (La1−xEux)2M2O7 (M=Zr, Hf, Sn) pyrochlores

Eu-doped pyrochlores, La₂M₂O₇ (M=Zr, Hf, Sn), were synthesized by solid-state reaction at a temperature range of 1473 and 1673 K, and their structures and optical properties were characterized by X-ray Rietveld analysis, field emission scanning electron microscope (FE-SEM), and photoluminescent spectroscopy. The Rietveld analysis indicated that the distortion of the (EuO₈)ⁿ⁻ scalenohedra increased with decreasing ionic radii of the M⁴⁺ ion, and the crystallinity increased with the sintering temperature. The splitting width of ⁵D₀-⁷F₁ transition of Eu³⁺ ions increased with the distortion of the (EuO₈)ⁿ⁻ scalenohedra. The luminescent intensity ratio of magnetic dipole transitions to electronic dipole transitions decreased with the crystallinity, and the chromaticity changed from deep-red to orange-red. The relationship between the chromaticity of phosphors and the crystallinity was clarified, and the control of crystallinity is an important factor that provides phosphors with required chromaticity.     

Theoretical investigation of the molecular structure and transition dipole moments of the NaK low lying electronic states

The electronic structure and the spectroscopic constants of the low lying electronic states of the NaK⁺ ionic molecule have been determined through using an ab initio approach involving a non-empirical pseudopotential for the Na and K cores and core valence correlation correction. The potential energy of nearly 26 electronic states of ²Σ⁺, ²Π, and ²Δ symmetries has been calculated up to their dissociation limit Na(4d) + K⁺ and Na⁺ + K(6s). Their spectroscopic constants (R_e, D_e, T_e, ω_e, ω_eχ_e, and B_e) are derived and compared with the few available theoretical studies. A good agreement has been found for the ground state and few excited states with previous works. New potential energy curves were presented, for the first time, for the higher excited states. Numerous avoided crossing between electronic states of ²Σ⁺, ²Π symmetries have been localized and analyzed. Their existences are related to the charge transfer between the two ionic molecules Na⁺K and NaK⁺. Furthermore, we have determined the transition dipole moments for several states and analyzed the avoided crossings related to charge transfer between alkaline atoms.