Effect of lithium ion content on the lithium ion conductivity of the garnet-like structure Li<Subscript>5+x</Subscript>BaLa<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>11.5+0.5x</Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0–2)

We report systematic studies on the transport properties by varying the lithium oxide content of the garnet-based solid electrolyte Li_5+xBaLa₂Ta₂O_11.5+0.5x (x=0, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00) for understanding the ionic conductivity dependence on the crystal lattice parameter and carrier concentration. Powder X-ray diffraction data of Li_5+xBaLa₂Ta₂O_11.5+0.5x (x=0, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00) indicate the existence of the garnet-like structure for any of the compositions. The cubic lattice parameter was found to increase with increasing x and reaches a maximum at x=1.00, then decreases slightly with a further increase in x. Impedance measurements obtained at 50 °C indicate a maximum of the grain-boundary resistance (R_gb) contribution to the total resistance (R_b+R_gb) at x=0.0 and a considerable decrease with increase in lithium concentration. The total (bulk + grain-boundary) and bulk ionic conductivity increase with increasing lithium content and reach a maximum at x=1.00 and then decrease slightly with further increase in x. Among the investigated compounds, Li₆BaLa₂Ta₂O₁₂ exhibits the highest total (bulk + grain-boundary) and bulk ionic conductivity of 1.5×10^-4 and 1.8×10^-4 S/cm at 50 °C, respectively. The results obtained in the present investigation of the Li_5+xBaLa₂Ta₂O_11.5+0.5x (x=0–2) series clearly revealed that the lithium content plays a major role in decreasing the grain boundary resistance contribution to the total resistance and also in increasing the ionic conductivity of the garnet-like compound. PACS 66.10.Ed; 82.45.Gj; 82.47.Aa     

The structure of mixed fluorides Ca1?xSrxF2 and Sr1?xBaxF2 and the luminescence of Eu2+ in these crystals

The structure of the mixed fluorites Ca_1−x Sr_xF₂ and Sr_1−x Ba_xF₂, as well as the structure of the Eu²⁺ impurity center in these crystals, is calculated within the framework of the virtual-crystal method realized in the shell model and pair-potential approximation. The phenomenological dependence of the position of the lower level of the 4f ⁶5d configuration of the Eu²⁺ ion on distance to the Eu²⁺-ligand is derived. The dependences of the Stokes shift and the Huang-Rhys factor on x are calculated for the yellow luminescence in Sr_1−x Ba_xF₂:Eu²⁺. The value of x at which the lower level of the 4f ⁶5d configuration of the Eu²⁺ ion in Sr_1−x Ba_xF₂:Eu²⁺ falls within the conduction band is found. __________ Translated from Fizika Tverdogo Tela, Vol. 45, No. 5, 2003, pp. 823–826. Original Russian Text Copyright ? 2003 by Nikiforov, Zakharov, Chernyshev, Ugryumov, Kotomanov.     

Thermal expansion of (Ba1 ? xLax)Ti1 ? x/4O3 solid solutions

Deformation and the thermal expansion coefficient of ceramic samples of (Ba_{1 − x} La _x )Ti_{1 − x/4}O₃ solid solutions (x = 0, 0.026, 0.036, 0.054) were studied in the temperature range 120–700 K. Based on an analysis of the data obtained, the temperature-composition phase diagram is refined, and the temperature dependence of the polarization is calculated. The results are discussed in combination with the dielectric measurement data. Original Russian Text ? M.V. Gorev, I.N. Flerov, Ph. Sciau, S. Guillemet-Fritsch, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 4, pp. 746–752.     

Magnetic properties of electron-irradiated quasi-layered manganites La2?2xSr1+2xMn2O7 (x=0.3, 0.35, 0.4)

The magnetic properties of La_2−2x Sr_1+2x Mn₂O₇ polycrystals (x=0.3–0.4) are studied over a broad temperature range 80–600 K. Quasi-two-dimensional manganites have a complex magnetic structure that undergoes several transitions from one type of magnetic ordering to another. A specific feature of these manganites is a hyperbolic dependence of inverse susceptibility in the transition region from the magnetically ordered to paramagnetic state for T>360 K. This suggests the onset of ferrimagnetism. Electron irradiation to a fluence Φ=1×10¹⁸ electrons/cm² is shown to have no effect on the long-range magnetic order while favoring the formation of paramagnetic polarons and of an inhomogeneous paramagnetic state. __________ Translated from Fizika Tverdogo Tela, Vol. 45, No. 8, 2003, pp. 1440–1445. Original Russian Text Copyright ? 2003 by Arbuzova, Naumov, Arbuzov.     

Unusually strong coherent response from grain-boundary Josephson network in polycrystalline PrxY1 ? xBa2Cu3O7 ? δ

By applying a highly sensitive homemade AC susceptibility technique to Pr _x Y_{1 − x} Ba₂Cu₃O_{7 − δ} polycrystals (with x = 0.0, 0.1, and 0.3), we observed very sharp Fraunhofer type low-field periodic oscillations of the real part of the AC susceptibility which were attributed to Josephson vortices penetrating intergranular regions of grain-boundary Josephson network in our samples. Assuming the Lorentz type distribution of single-junction contact areas, we were able to successfully fit the experimental data.     

Characterisation of Ba2In2 − x Sn x O5 + x/2 oxide ion conductors

The Ba₂In_2 − x Sn _x O_5 + x/2 solid solution was confirmed up to x = 1 by solid-state reaction. X-ray diffraction at room and at elevated temperatures, Raman scattering and impedance spectroscopy were used to characterise the samples. The structure refinement of the composition x = 0.1 from neutron diffraction data reveals that tin is preferentially located in the tetrahedral layers of the brownmillerite. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007     

Giant dielectric relaxation in SrTiO3-SrMg1/3Nb2/3O3 and SrTiO3-SrSc1/2Ta1/2O3 solid solutions

Ceramic samples of (1−x)SrTiO₃-xSrMg_1/3Nb_2/3O₃ and (1−x)SrTiO₃-xSrSc_1/2Ta_1/2O₃ were prepared, and their dielectric properties were studied at x=0.005–0.15 and 0.01–0.1, respectively, at frequencies 10 Hz–1 MHz and at temperatures 4.2–350 K. A giant dielectric relaxation was observed in the temperature range 150–300 K, and not so strong but well-developed relaxation was found in the temperature range 20–90 K. The activation energy U and the relaxation time τ₀ were determined to be 0.21–0.3 eV and from 10⁻¹¹ to 10⁻¹² s for the high-temperature relaxation and 0.01–0.02 eV and 10⁻⁸–10⁻¹⁰ s for the low-temperature relaxation, respectively. The additional local charge compensation of the heterovalent impurities Mg²⁺ and Nb⁵⁺ (or Sc³⁺ and Ta⁵⁺) by free charge carriers or the host ion vacancies is suggested to be the underlying physical mechanism of the relaxation phenomena. On the basis of this mechanism, the Maxwell-Wagner model and the model of reorienting dipole centers Mg²⁺ (or Sc³⁺) associated with the oxygen vacancy are proposed to explain the high-temperature relaxation with some arguments in favor of the latter model. The polaron-like model with the Nb⁵⁺-Ti³⁺ center is suggested as the origin of the low-temperature relaxation. The reasons for the absence of ferroelectric phase transitions in the solid solutions under study are also discussed. From Fizika Tverdogo Tela, Vol. 44, No. 11, 2002, pp. 1948–1957. Original English Text Copyright ? 2002 by Lemanov, Sotnikov, Smirnova, Weihnacht. This article was submitted by the authors in English.     

Electron spin resonance of localized copper states in Sr1?xAxCuO2 ceramics (A = Li+, K+, La3+; x ≤ 0.15)

The orthorhombic modification of SrCuO₂ ceramics and its derivatives Sr_1−x A _x CuO₂ (A = Li⁺, K⁺, La³⁺) were studied using the ESR and x-ray diffraction methods. Orthorhombic and axial-symmetry paramagnetic centers caused by oxygen defects in samples were detected. From comparing the ESR and x-ray phase data, it follows that the oxygen distribution in ceramics is inhomogeneous. __________ Translated from Fizika Tverdogo Tela, Vol. 47, No. 8, 2005, pp. 1482–1485. Original Russian Text Copyright ? 2005 by Ivanova, Jacyna-Onyszkiewicz, Augustyniak-Yablokova, Yablokov, Shustov.     

Layered LiCo1?xMgxO2 (x = 0.0, 0.1, 0.2, 0.3 and 0.5) cathode materials for lithium-ion rechargeable batteries

Layered LiCo_1−x Mg _x O₂ (x = 0.0, 0.1, 0.2, 0.3 and 0.5) oxide materials were synthesized using LiNO₃, Co(NO₃)₂, Mg(NO₃)₂ as the precursors, and the effect of the dopants on the electrochemical properties was investigated. thermogravimetric/differential thermal analysis was carried out to observe the phase transformations of LiCo_0.9Mg_0.1O₂. The phase purity and cation environment of the synthesized oxides were characterized using X-ray diffraction and Fourier transform infrared spectroscopy. The particle size, nature, morphological properties and composition of the synthesized oxides were examined by TEM and SEM with energy dispersive X-ray spectroscopic analysis. Finally, the electrochemical behavior of the prepared layered materials was studied using cyclic voltammetry and charge–discharge cycling. LiCo_0.8Mg_0.2O₂ has good cycling results when compare to other doped and undoped materials. These results have been also supported by cyclic voltammograms.     

Synthesis and study of photocatalytic activity of nanoscale quasi-one-dimensional Ti1 ? xVxO2 (0 ≤ x ≤ 0.13) and Zn1 ? xCoxO (0 ≤ x ≤ 0.3) oxides

A original method of synthesis of quasi-one-dimensional Ti_{1 − x} V _x (OCH₂CH₂O)₂ (0 ≤ x ≤ 0.13) and Zn_{1 − x} Co _x (HCOO)(HOCH₂CH₂O) (0 ≤ x ≤ 0.3) has been developed. The synthesis products were used as a basis for nanoscale extended Ti_{1 − x} V _x O₂ and Zn_{1 − x} Co _x O oxides. The compounds obtained and products of their thermolysis were investigated by X-ray diffraction, microscopy, IR spectroscopy, thermogravimetry, and chemical analysis; the shape and size of particles were determined by scanning electron microscopy. The good prospects of Ti_{1 − x} V _x O₂ and Zn_{1 − x} Co _x O solid solutions as photocatalysts for hydroquinone oxidation are shown.