Cationic nonstoichiometry of oxides of the Ba-Cu-O and Y-Ba-Cu-O systems

The structure and cationic composition of oxides of the Ba-Cu-O system with cubic BaCuO₂ and tetragonal BaCu₂O₂ structure and YBa₂Cu₃O_{6 + ??} oxide of the Y-Ba-Cu-O system are studied. The oxides are found to be nonstoichiometric in cationic composition when the composition differs noticeably from the corresponding formula relation with conservation of the crystalline structure??s type.     

How amorphous are the tin alloys in li-inserted tin oxides?

Several different metal oxides based anode systems are compared to give insight into their cycling behaviour. The simple electrochemical model for these systems does not usefully predict the ability for a battery to cycle. Pb and Zn oxides cycle less well than Sn oxides, and show more initial crystallinity. SnF₂ and PbF₂ cycle less well than SnO and PbO. Cubic SnP₂O₇ cycles better than the layered polymorph. The nature and structure of the supporting matrix is therefore important in the ability of the tin oxides to cycle. Any material with observable crystallinity in first cycle, will not cycle well. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Dopability, intrinsic conductivity, and nonstoichiometry of transparent conducting oxides

Existing defect models for In(2)O(3) and ZnO are inconclusive about the origin of conductivity, nonstoichiometry, and coloration. We apply systematic corrections to first-principles calculated formation energies Delta H, and validate our theoretical defect model against measured defect and carrier densities. We find that (i) intrinsic acceptors ("electron killers") have a high Delta H explaining high n-dopability, (ii) intrinsic donors ("electron producers") have either a high Delta H or deep levels, and do not cause equilibrium-stable conductivity, (iii) the O vacancy V(O) has a low Delta H leading to O deficiency, and (iv) V(O) has a metastable shallow state, explaining the paradoxical coexistence of coloration and conductivity.     

Mössbauer study on indium tin oxides (ITO) doped with Fe

InSnFe mixed oxides were prepared by a sol–gel method, and were investigated by Mössbauer spectrometry and magnetization measurements. The magnetic relaxation peaks in addition to paramagnetic peaks were observed in Mössbauer spectra. Most of Fe^3?+? species (D1) occupy 24d site of bixbyite structure, and the other Fe^3?+? species (D2) occupy 8b site. The area intensity ratio of two doublets for sample with x?=?0.06 and y?=?0.06 was most perfectly consistent with the ratio of d/b site occupations (24/8); this sample showed the highest magnetization among these samples. Fired ash of In oxide (5%Fe), which showed ferromagnetism, consisted of γ Fe₂O₃ segregated oxides.     

Sn Mössbauer spectroscopic study of nanometric tin dioxide powders prepared by pyrolysis of organotin oxides

This paper reports the results of ¹¹⁹Sn Mössbauer Spectroscopy of residues from the pyrolysis of Sn₃O₃Bu₆ (1) and Sn₄O₆Bu₄ (2) (Bu=n-butyl) in air, O₂, and N₂. The isomer shift and quadrupole splitting parameters of the samples allowed the identification of the tin oxidation states, as well as the number of non-equivalent coordinated tin sites. The result of the ¹¹⁹Sn Mössbauer study correlates perfectly with those of X-ray electron probe microanalysis, scanning electron microscopy and X-ray powder diffraction for the formation of pure SnO₂ from the decomposition of (1) and (2) in air or O₂. However, in N₂, evidences suggest the formation of a mixture of SnO₂ and SnO.     

TDPAC characterization of tin oxides using181Ta

In connection with a general study of the evolution of tin-oxygen thin films, we report here on the hyperfine interactions of¹⁸¹Ta substitutionally replacting tin in the isolated phases SnO and SnO₂. For this purpose, pure SnO pressed powder and a thin SnO₂ film were implanted with¹⁸¹Hf. In both cases, unique quadrupole frequencies were found after thermal annealing treatments. The results indicate that the following hyperfine parameters: υ _Q = 740.6(2.1) MHz, η=0.07(2) and υ _Q = 971.5(1.9) MHz, η=0.72(1) characterize¹⁸¹Ta in SnO and SnO₂, respectively.     

A study of dilute tin alloys by x-ray photoelectron spectroscopy

X-ray photoelectron spectra of Pb₉₈Sn₂, Ag₉₅Sn₅, Sb₉₅Sn₅ and Cd_99.6Sn_0.4 have been recorded using a VG Scientific ESCA-3 Mk. II electron spectrometer. In all cases the Sn 3d level in the alloys is compared with the 3d level in pure tin. The binding energy shifts are explained on the basis of electronegativity and near-neighbour interactions. It is found that increased coordination number as well as increased electronegativity of the neighbouring atoms increases the binding energy of the core electron level.     

Structure and stability of a homologous series of tin oxides

The structures and stabilities of a series of nonstoichiometric SnO2-x compounds, which are yet unknown experimentally, are predicted using the cluster expansion technique combined with first-principles calculations. A homologous series of Sn(n+1)O(2n) in which oxygen vacancies are layered on (101) planes of the rutile lattice is discovered. The homologous crystals are composed of divalent and quadrivalent Sn atoms. No trivalent Sn atoms are formed.     

A study on the solubility and distribution of carbon in oxides

Measurements of radiocarbon in oxides were conducted after annealing single crystalline und polycrystalline FeO, Fe₃O₄, MnO, MgO, Cr₂O₃ and Al₂O₃ in radioactive CO₂-CO mixtures at 1000°C for different times. Concentrations of ≥ 0.01 wt. ppm C could be detected by anticoincidence counting and the distribution was observed by autoradiography. The measurements showed no carbon (< 0.01 ppm) in the lattice or the grain boundaries of pore- and crack-free oxides, carbon was detected only in cracks, pores or in grain boundaries which had cracked open. Thus, there is no measurable solubility of carbon in the bulk oxides for all the different chemical compositions investigated. Permeation of carbon through oxide layers on metals and alloys can only occur by transport of carbon-bearing molecules through cracks and pores of the oxide.     

Promoting effect of tin oxides on alumina-supported gold catalysts used in CO oxidation

In this study the influence of SnO_x nanoparticles on the catalytic performance of alumina-supported gold catalysts was investigated in CO oxidation. The tin modified supports were prepared by grafting of tetraethyltin onto the surface of alumina via its hydroxyl groups. The decomposition of organometallic surface species in oxygen yielded highly dispersed tin oxide on the surface of alumina. Gold was introduced onto the tin modified alumina support by both deposition-precipitation with urea and direct anionic exchange techniques using HAuCl₄ solution. Based on catalytic and different spectroscopic measurements it is suggested that the presence of “Snⁿ⁺-Au ensemble sites” is responsible for the increased activity of these catalysts.     

A Rutherford scattering study of the chemical composition of native oxides on GaP

The chemical compositions of two types of protective oxide films on single crystal GaP have been studied by Rutherford backscattering (2 MeV He⁺) combined with ion channeling. Films of 350–1400 Å thickness were grown by immersing GaP slices in hydrogen peroxide, with or without externally applied anodic bias. Films grown by a galvanic coupling process have compositions of about 1:1·1:4·5 (Ga:P:O) and are believed to be vitreous mixtures of Ga₂O₃+P₂O₅. Films grown with anodic bias exhibited a deficiency of Ga in a ～200 Å region at the GaP-oxide interface.     

Photoemission study of oxygen chemisorption on tin

Photoemission measurements have been made at photon energies from 5–12 eV and at 21.2 eV on evaporated Sn films and the same films with varying room temperature exposure to oxygen. For hν ? 9 eV the quantum yield for Sn with exposures of as much as 4000 L oxygen (1 L = 1 Langmuir = 10^?6 Torr sec) differs only slightly from the clean metal. For hν ? 9 eV no change in yield is observed with oxygen exposure. The energy distribution of photoemitted electron (EDC's) from Sn with increasing exposure to oxygen above ? 20 L are characterized by the growth of two peaks which were not present in the EDC's for the clean metal, located 2.9 ± 0.1 eV and 4.8 ± 0.1 eV below the Fermi level. We associate this structure with the presence of SnO₂. No sharp resonance which could be associated with adsorbed oxygen was seen. Uniformly reduced emission from metallic Sn states and a Fermi level as sharp as for the clean metal is observed in the EDC's at all oxygen exposures. In addition, no change in work function with oxygen exposure was detected. The effects of oxygen saturate for exposures ? 4000 L. We suggest that under the conditions used in this experiment, the oxygen penetrates beneath the surface forming SnO₂ and leaving metallic Sn on the surface.     

A semi-empirical equation for oxygen nonstoichiometry of perovskite-type ceramics

Explicit equations correlating oxygen nonstoichiometry to oxygen partial pressure and temperature are important for applications of perovskite-type ceramics as membranes, adsorbents and catalysts in various chemical reaction and separation processes. A semi-empirical equation for oxygen nonstoichiometry on perovskite-type ceramics is reported in this paper. Though derived from the results of a point defect model on a perovskite-type ceramic material, La_0.1Sr_0.9Co_0.5Fe_0.5O_3−δ, this equation describes very well the experimentally measured oxygen nonstoichiometry data for two perovskite-type ceramics measured in this work and three perovskite-type ceramics reported in the literature. The major advantage of this semi-empirical equation lies in its simplicity, explicitness and accuracy. This equation is coupled with oxygen permeation equation to predict oxygen permeation current density through two perovskite-type ceramic membranes. The predicted data agree very well with the results reported in the literature using a complex defect reaction model.     

A study of the (3He,n) reaction on isotopes of tin

The (³He, n) reaction has been studied on^{112,116,118,120,124}Sn at 25.4 MeV. Angular distributions were measured over the range 0°–25° and the results compared with predictions of zero-range DWBA calculations. In addition to the around-state transitions, L = 0 transitions were also observed to low-lying states in every case. Simple two component wave functions, as well as those obtained from a more sophisticated pairing model, are compared with the data in order to explain the appearance of the anomalously low-lying excited 0⁺ states observed. L = 2 transitions were observed to low-lying 2⁺ states, but the strength of these transitions was much less than expected from the systematics of (t, p) results for N = 50 nuclei.     

水合金属氧化物对氟的吸附机理研究

通过碱沉淀法制备了Ce,Al,Ni,Cu的水合氧化物,研究了它们的Langmuir吸附等温线,并利用BET法通过吸附-脱附氮气测定了其比表面积,同时对其吸附氟离子前后的变化进行了IR谱图的表征.结果表明不同水合金属氧化物具有不同的比表面积,其孔径分布也不尽相同,吸附量与比表面积之间没有直接相关的正比关系.吸附等温线均符...     

金属锡表面吸附氢同位素的量子力学计算

根据原子分子反应静力学与群论,确定了H2、D2和T2的基电子状态为1∑+g(D∞v),SnH、SnD和SnT的基电子状态为2∑+( C∞v).应用基函数SDD**和6-311G**,密度泛函B3P86方法,计算了氢同位素分子及其锡化物的结构、能量E、定容热容Cv和熵S.H2 (D2, T2) ,SnH(D , T)和SnH2(D2, T2)的基电子状态分别为1∑+g(D∞h ),2∑+(C∞v)和3B1(C2v).H2、D2和T2的离解能为4.591 8 eV,SnH(D, T)分子的离解能为2.714 7 eV,SnH2(D2, T2)分子的离解能为4.833 9 eV.用总能量中的电子和振动能量近似代表SnHn、SnDn和SnTn(n=1,2)分子处于固态时的能量,用总熵中的电子和振动熵近似代表SnH、 SnD和SnT分子处于固态时的熵,从而计算了锡与H2、D2和T2反应过程的△Hf°,△Sf°,△Gf°和平衡压力, 并导出他们与温度的函数关系.X     

Oxygen nonstoichiometry in high-Tc superconductor HoBa2Cu3O6+x and application of coulometric tritration

Nonstoichiometry in the perovskite-type compound, HoBa₂Cu₃O_6+x, was determined as a function of oxygen partial pressure (5 × 10⁻¹ 1 × 10⁵ Pa) in the temperature range of 8631173 K by coulometric titration using a stabilized zirconia electrolyte. Electromotive force of the cell, EMF, was measured as a function of oxygen content at constant temperature, and as a function of temperature at constant oxygen content. The perovskite-type compound was found to have a tendency to decompose into Ho₂O₃, BaO, CuO and some double-oxides at low oxygen partial pressures. Defect equilibria are discussed on the basis of the dependence of nonstoichiometry on oxygen partial pressure. Variation of the relative partial molar entropy with composition is explained in terms of a well-known defect model. A new technique which was developed for measuring the electrical conductivity of a non-stoichiometric oxide, in situ, at constant oxygen content as a function of temperature in the coulometric titration cell, is presented.