Al,F-doped new perovskite lithium fast ion conductor Li3x La2/3−x□1/3−2x Ti1−y Al y O3−y F y (x=0.11)

Al, F-doped new perovskite lithium ion conductors (x=0.11) have been prepared by solid state reaction. It is found that a pure perovskite-structured phase with space group of P4mm(99) exits in the composition range of 0<y≤0.10. The sample with y=0.02 possesses the highest ionic conductivity of 1.06×10⁻³ S/cm at room temperature, and its decomposing voltage is 2.3 V. The factors affecting the conductivity of this system are discussed.     

Pre-exponential factor of the hopping conductivity in disordered carbon films

The conductivity of carbon films grown by polymethylphenylsiloxane vapor decomposition in stimulated dc discharge plasma was studied. It is found that the Mott hopping conductivity $ \sigma \left( T \right) = \sigma _0 \left( T \right)\exp \left\{ { - \frac{{T_0 }} {T}^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} } \right\} $ \sigma \left( T \right) = \sigma _0 \left( T \right)\exp \left\{ { - \frac{{T_0 }} {T}^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} } \right\} is characteristic of the samples under study in the temperature range of 80–400 K in the electric field E to 5 · 10⁴ V/cm. An analysis of the pre-exponential factor σ ₀(T) = σ ₀₀(T ₀)T ^α allowed the conclusion that the hopping transport is most adequately described in the model with the exponential energy dependence of the density of localized states for which α = −1/2 and the universal relation ln σ ₀₀ −T ₀^1/4 0 is valid, which is satisfied in the range where the parameter σ ₀₀ varies by eight orders of magnitude.     

NMR Studies on the Internal Structure of High-T c Superconductors and Other Anorganic Compounds

Spatially-resolved NMR is used to probe internal structures in highly correlated superconductors of optimally-doped (T _c = 85 K) and a heavy fermion superconductor CeCoIn₅ (T _c = 2.3 K). The characteristic change of the properties of ²⁰⁵Tl-NMR in the vortex state provides a clear evidence of the antiferromagnetic order in the vortex cores below 20 K in . We also obtain anomalous ¹¹⁵In-NMR spectra of CeCoIn₅, which provides a microscopic evidence for the occurrence of a spatially-modulated superconducting order parameter expected in a Fulde–Ferrel–Larkin–Ovchinnkov (FFLO) state.     

Oxygen ion transport numbers: assessment of combined measurement methods

Several modifications of the faradaic efficiency and electromagnetic field (EMF) methods, taking electrode polarisation resistance into account, were considered based on the analysis of ion transport numbers and p-type electronic conductivity of ceramics at 973–1,223 K. In air, the activation energies for p-type electronic and oxygen ionic transport are 115 ± 9 and 71 ± 5 kJ/mol, respectively. The oxygen ion transference numbers vary in the range 0.992–0.999, increasing when oxygen pressure or temperature decreases. The apparent electronic contribution to the total conductivity, estimated from the classical faradaic efficiency and EMF techniques was considerably higher than true transference numbers due to a non-negligible role of interfacial exchange processes. The modified measurement routes give reliable and similar results when p(O₂) values at the electrodes are high enough, whilst decreasing the oxygen pressure leads to a systematic error for all techniques associated with measurements of concentration cell EMF. This effect, presumably due to diffusion polarisation, increases with decreasing temperature. The most reliable results in the studied p(O₂) range were provided by the modified faradaic efficiency method.     

Measurement of the running of the QED couplingin small-angle Bhabha scattering at LEP

Using the OPAL detector at LEP, the running of the effective QED coupling α(t) is measured for space-like momentum transfer from the angular distribution of small-angle Bhabha scattering. In an almost ideal QED framework, with very favourable experimental conditions, we obtain: where the first error is statistical, the second is the experimental systematic and the third is the theoretical uncertainty. This agrees with current evaluations of α(t). The null hypothesis that α remains constant within the above interval of -t is excluded with a significance above 5σ. Similarly, our results are inconsistent at the level of 3σ with the hypothesis that only leptonic loops contribute to the running. This is currently the most significant direct measurement where the running α(t) is probed differentially within the measured t range. Received: 2 March 2005, Revised: 30 August 2005, Published online: 3 November 2005     

Critical behavior of La0.67−y (Sr, Ba, Ca)0.33+y Mn1−x Sn x O3 (x = 0.01, 0.02, y = 0, 0.07) perovskites

The magnetic critical behavior of the manganese perovskite series $ {\text{La}}_{{0.67 - y}} {\left( {{\text{Sr,}}\,\,{\text{Ba,}}\,\,{\text{Ca}}} \right)}_{{0.33 + y}} {\text{Mn}}_{{1 - x}} {\text{Sn}}_{x} {\text{O}}_{3} The magnetic critical behavior of the manganese perovskite series (x = 0.01, 0.02, y = 0, 0.07) is studied by means of dc magnetic measurements and ¹¹⁹Sn M?ssbauer spectroscopy. The structure can be described by a rhombohedral unit cell (space group R–3C) for the samples where the A-site is occupied by La and Sr or La and Ba ions and orthorhombic unit cell (space group Pnma) for the samples where the A-site is occupied by La and Ca ions. Arrott and scaling plots show that the samples, where the A-site is occupied by La and Sr or La and Ba ions, follow the behavior of a conventional second-order ferromagnetic transition. In contrast, the samples that contain La and Ca ions in the A-site show anomalous behavior around Curie point. M?ssbauer measurements show two magnetic phases below T _c. One of them exhibits stronger exchange interactions with more rapid electron transfer between Mn³⁺/Mn⁴⁺, compared to the other.     

Determination of heavy quark non-perturbative parametersfrom spectral moments in semileptonic B decays

Moments of the hadronic invariant mass and of the lepton energy spectra in semileptonic B decays have been determined with the data recorded by the DELPHI detector at LEP. From measurements of the inclusive b-hadron semileptonic decays, and imposing constraints from other measurements on b- and c-quark masses, the first three moments of the lepton energy distribution and of the hadronic mass distribution, have been used to determine parameters which enter into the extraction of |V_cb| from the measurement of the inclusive b-hadron semileptonic decay width. The values obtained in the kinetic scheme are: and include corrections at order 1/m_b³. Using these results, and present measurements of the inclusive semileptonic decay partial width of b-hadrons at LEP, an accurate determination of |V_cb| is obtained: Received: 26 April 2005, Revised: 16 September 2005, Published online: 16 November 2005     

Measurements of the electronic conductivities of In-doped CaZrO<Subscript>3</Subscript> by a DC polarization technique

The following hydrogen and oxygen concentration cells using the oxide protonic conductors, \textCaZ\textr_0.98\textI\textn_0.02\textO_{3 - d} {\text{CaZ}}{{\text{r}}_{0.98}}{\text{I}}{{\text{n}}_{0.02}}{{\text{O}}_{3 - \delta }} and \textCaZ\textr_0.9\textI\textn_0.1\textO_{3 - d} {\text{CaZ}}{{\text{r}}_{0.{9}}}{\text{I}}{{\text{n}}_{0.{1}}}{{\text{O}}_{{3} - \delta }} , as the solid electrolyte were constructed, and their polarization behavior was studied,

Transport properties of CsHSO4 investigated by impedance spectroscopy and nuclear magnetic resonance

Transport properties of the superprotonic conductor, CsHSO₄, have been investigated by impedance spectroscopy and nuclear magnetic resonance (NMR). It has been found that both, conductivity (σ) and NMR diffusion (D _NMR) are practically isotropic in the high-conductive (superprotonic) phase (above 414 K). The NMR diffusion coefficient, D _NMR , increases rapidly and discontinuously at the melting point (~490 K). The temperature change of D _NMR in the superprotonic phase is characterized by a smaller activation energy compared to that in the liquid state. The values calculated from the Nernst-Einstein relation practically coincide with D _NMR in the superprotonic phase, i.e., the Haven ratio is close to unity. This indicates that in this phase the proton motion is rather uncorrelated.     

A-site deficient lanthanum-calcium chromite-titanates doped with 3d transition metals: synthesis,oxygen nonstoichiometry,electrical conductivity,and catalytic activity

Six (M = Cr, Mn, Fe, Co, Ni, Cu) and two (M = Ni, Cu) single-phase compositions were prepared by conventional solid-state reactions. Oxygen nonstoichiometry, electrical conductivity, phase transformations under reduction-reoxidation at high temperatures and catalytic activity for hydrocarbons oxidation of these compositions were investigated in a wide temperature and oxygen partial pressure range. The Cu-, Ni-, Co-, and Fe-containing compositions are decomposed in reducing Ar/H₂O/H₂ atmosphere with pH₂O / pH₂ = 0.3 at 1,000 °C, while the Cr- and Mn-containing ceramics remain stable at the same conditions. The metallic particles of the added 3d elements formed after decomposition were registered by X-ray diffraction method in case of Cu- and Ni-containing compositions. These formed composites can be completely reoxidized with formation of initial compositions by treatment in air at 1,000 °C. The electrical conductivity of the ceramics investigated in air and Ar/H₂O/H₂ gas flow increases with rising M content. The highest catalytic activity for oxidation of CH₄ and C₃H₆, which was comparable with the activity of the composite, shows the Cu-containing powders. Dedicated to Prof. Dr. Werner Weppner     

Spectral Measure of Heavy Tailed Band and Covariance Random Matrices

We study the asymptotic behavior of the appropriately scaled and possibly perturbed spectral measure of large random real symmetric matrices with heavy tailed entries. Specifically, consider the N × N symmetric matrix whose (i, j) entry is , where (x _ij , 1 ≤ i ≤ j < ∞) is an infinite array of i.i.d real variables with common distribution in the domain of attraction of an α-stable law, , and σ is a deterministic function. For random diagonal D _N independent of and with appropriate rescaling a _N , we prove that converges in mean towards a limiting probability measure which we characterize. As a special case, we derive and analyze the almost sure limiting spectral density for empirical covariance matrices with heavy tailed entries. Supported in part by a Discovery grant from the Natural Sciences and Engineering Research Council of Canada and a University of Saskatchewan start-up grant. Research partially supported by NSF grant #DMS-0806211.     

Small magnetic polaron effect in lithium iron phosphates

The small polarons in LiFePO₄ are associated with the presence of Fe³⁺ ions introduced by the native defects in relative concentration in the samples known to be optimized with respect to their electrochemical properties. The nearest iron neighbours around the central polaron site are spin-polarized by the indirect exchange mediated by the electronic charge in excess. These small magnetic polarons are responsible for the interplay between electronic and magnetic properties that are quantitatively and self-consistently analysed. Comparison is made with other magnetic polaron effects in other members of the family of magnetic semiconductors to which this material belongs. Paper presented at the 11th Euro-Conference on Science and Technology of Ionics, Batz-sur-Mer, France, 9–15 September 2007.     

Maximal Inequalities for CIR Processes

Let X be a Cox—Ingersoll—Ross (CIR) process given by

Oxidation of Pyrite Grains: A Mössbauer Spectroscopy and Mineral Magnetism Study

Fe²⁺ in pyrite is found in a low-spin d⁶ configuration, a necessary condition for diamagnetic and semi-conducting properties of material. The semi-conducting property of pyrite has been studied since the time when pyrite was used as a rectifier in early radios. Pyrite posses the highest possible crystal field stabilisation energy and offers a better altemative as solar material compared to Si-based materials. Unfortunately, pyrite is difficult to study due to its inherent deviation from stoichiometry and its ease of oxidation. Since pyrite and its oxidation products are all Fe-bearing phases, combining Mössbauer spectroscopy with mineral magnetic methods provides enough information to monitor the oxidation of pyrite in air and identify the different phases produced and their relation to different experimental parameters. For mm-sized grain samples, heating FeS₂ at temperatures between 450 °C and 650 °C five different mineral assemblages are identified. FeS₂ is oxidized to α-Fe₂O₃ along two separate routes: $${\text{FeS}}_{2} \to {\text{FeSO}}_{4} \to \varepsilon {\text{ - Fe}}_{2} {\text{O}}_{3} \to \alpha {\text{ - Fe}}_{2} {\text{O}}_{3} ;\;{\text{and}}$$ $${\text{FeS}}_{2} \to {\text{FeSO}}_{4} \to {\text{Fe}}_{2} {\left( {{\text{SO}}4} \right)}_{3} \to \beta {\text{ - Fe}}_{2} {\text{O}}_{3} \to \alpha {\text{ - Fe}}_{2} {\text{O}}_{3} $$      

Diffusion of proton in alumina-rich nonstoichiometric magnesium aluminate spinel

The phenomenon of the diffusion of proton and deuteron in a single crystal of magnesium aluminate spinel was studied by infrared absorption. The chemical diffusion coefficient of proton was determined by the relaxation time of the absorption intensity upon the substitution of deuteron with proton. The temperature dependence of the chemical diffusion coefficient of proton for was expressed as . The chemical diffusion coefficient of proton was found to be independent of the composition of spinel and of the atmosphere. Paper presented at the 11th Euro Conference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15 2007.     

Search for new oxide-ion conducting materials in the ceria family of oxides

We have adopted a modified combustion route, namely, a mixed fuel process (MFP) to prepare a novel series of nano-crystalline single- and multiple-doped ceria compositions with controlled powder characteristics, large surface area, finer particle size, high sinterability, and high oxide ion conductivity at intermediate temperatures (500–700 °C). Using the mixed fuel process, we have prepared nano-particles of single- and multiple-doped ceria powders with dopants such as Ca, Gd, and Sm and a suitable combination of the same. In the pursuit for identifying new oxide-ion-conducting materials in this family of oxides, we have pursued the idea of co-doping effect on the single doped compositions with proper introduction of a second dopant. Effect of these dopants on the thermal decomposition and physico–chemical characteristics of the precursor and the powders prepared thereby were studied in detail. Finally, the effects of multiple co-doping on the microstructural and electrical properties were compared to understand the origin of the effect of dopant characteristics on the oxide ion conductivity of Ce_1−x M _x O₂ solid solutions. Our experimental results established unequivocally that co-doping is very effective in identifying new materials with remarkably high ionic conductivity with substantial reduction in the cost for technological applications. Among the studied compositions, the maximum conductivity with minimum activation energy was observed for the triply co-doped CCGS composition (; E _a = 0.56 eV), which is much higher compared to the conductivity exhibited by most of the reported co-doped ceria compositions. In conclusion, an effective way to improve the oxide ion conductivity of ceria-based oxides by proper choice of dopants and co-doping is achieved.     

The direct precipitation of rhabdophane (REEPO<Subscript>4</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O) nano-rods from acidic aqueous solutions at 5–100 °C

The precipitation of lanthanum and neodymium phosphate phases from supersaturated aqueous solutions at pH ~1.9 was studied at 5, 25, 50, and 100 °C in batch reactors for up to 168 h. Crystalline La and Nd–rhabdophane phases precipitated immediately upon mixing of the initial aqueous La or Nd and PO₄ solutions. Changes in aqueous PO₄ and Rare Earth Element (REE) concentrations during the experiments were determined by ICP-MS and UV–Vis spectrophotometry, while the resulting solids were characterized via powder XRD, SEM, TEM, and FTIR. All precipitated crystals exhibited a nano-rod morphology and their initial size depended on temperature and REE identity. At 5 °C and immediately after mixing the La and Nd–rhabdophane crystals averaged ~44 and 40 nm in length, respectively, while at 100 °C lengths were ~105 and 94 nm. After 168 h of reaction, the average length of the La and Nd rhabdophanes increased by 23 and 53% at 5 °C and 11 and 59% at 100 °C, respectively. The initial reactive solutions in all experiments had activity quotients for rhabdophane precipitation: \textREE ³⁺ + \textPO₄^{3 -} + n\textH₂ \textO = \textREEPO₄ ·  n\textH₂ \textO {\text{REE}}^{ 3+ } + {\text{PO}}_{4}^{3 - } + n{\text{H}}_{2} {\text{O}} = {\text{REEPO}}_{4} \cdot\;n{\text{H}}_{2} {\text{O}} of ~10^−20.5. This activity quotient decreased with time, consistent with rhabdophane precipitation. The rapid equilibration of rhabdophane supersaturated solutions and the progressive rhabdophane crystal growth observed suggests that the REE concentrations of many natural waters may be buffered by rhabdophane precipitation. In addition, this data can be used to guide crystallization reactions in industrial processes where monodisperse and crystalline La or Nd rhabdophane materials are the target.     

Changes in the Luminescent Properties of Humic Acids Induced by UV Radiation

Humic acids (HA) are complex, dark, paramagnetic biopolymers, ubiquitus in the soil and aquatic ecosystems. Due to their peculiar properties (multifluorophore system capable of excitation energy transfer, continuous featureless absorption over a wide spectral range, and paramagnetism), HA play an important role as an efficient target for UV solar radiation, O₂, and O₃—detrimental environmental factors which affect the Earth's biosphere. Photooxidation of HA causes changes in the absorption and luminescence properties of HA which may be of significant importance for environmental photophysics and photochemistry. We have studied effects of UV irradiation on the degradation of several commercial HA (Fluka, Merck, and Serva). Aqueous, aerated alkaline solutions of HA (0.1–0.4 g/L in 0.006–0.1 M Na₂CO₃) were irradiated with an electrodeless Hg (254-nm) lamp in a flow system during several hours. After different times of irradiation, solutions were assayed by means of fluorescence (Fl), absorption (UV–Vis), and chemiluminescence (CL) spectroscopy. The data obtained indicate that the free radical-mediated degradative photooxidation of HA macromolecules is accompanied by a very weak, long-lived chemiluminescence (340–800 nm), a gradual decrease in absorbancy with characteristic changes in color coefficients Q _4/6, Q _2.7/6.0, and Q _2.7/4.0, and an increase in the intensity of Fl emission (340- to 560-nm) and excitation (250- to 400-nm) spectra. Processes undergoing these changes are intrinsically associated with the generation of excited states and reactive oxygen species . These processes are expected to play a vital role in the natural environment, e.g., HA-photosensitized decomposition of xenobiotics and solar energy transfer in symbiotic hydrobionts.     

Thermoelectric power of YBa2Cu3Ox in equilibrium with gas phases

Thermoelectric power (TP) and electrical conductivity (EC) measurements were performed for YEa₂Cu₃O_x at 1128 K under controlled oxygen partial pressure varying between 50 and 10⁵ Pa. Three regimes are observed for the electrical properties. At low both TP and EC remain constant with . In the medium range sharp changes of both electrical parameters occur; TP changes sign from positive above 4×10² Pa to negative below this value. In the high region (>7.6×10³ Pa) TP vs log exhibits two slopes; 5.1 below 1.5×10⁴ Pa and 8.4 above this value. The slopes can be discussed in terms of the defect structure involving singly and doubly ionized oxygen vacancies below and above 7.6×10³ Pa, respectively.     

A stable and easily sintering {\text{BaCe}}_{0.7} {\text{Sn}}_{0.1} {\text{Gd}}_{0.2} {\text{O}}_{3 - \delta } electrolyte for solid oxide fuel cells

${\text{BaCe}}_{0.7} {\text{Sn}}_{0.1} {\text{Gd}}_{0.2} {\text{O}}_{3 - \sigma } $ (BCSG) and ${\text{BaCe}}_{0.8} {\text{Gd}}_{0.2} {\text{O}}_{3 - \sigma } $ (BCG) powders were prepared by solid-state reaction method. After exposure in 5% CO₂?+?5% H₂O?+?90% N₂ at 500 °C for 5 h, the BCSG powders were hardly affected while the BCG powders decomposed into CeO₂ and BaCO₃ phases. Moreover, the relative density of BCSG reaches 97%, while the BCG just displays 91% after sintering at 1,400 °C. The BCSG displays a conductivity of 0.01 S/cm at 700 °C in humid hydrogen, which is quite close to 0.012 S/cm for BCG. A fuel cell with BCSG exhibits 1.02 V for open circuit voltage, 420 mW/cm² for peak performance and 0.23 Ω cm² for interfacial resistance at 700 °C, respectively.