Classement des porteurs de charge et conductivite du compose K8Na4Sb12O36 de structure KSbO3 cubique

Two structures have been reported for cubic KSbO₃ type. One has space group Pn3, where K⁺ ions are in an ordered state. The other has Im3 with K⁺ ions in a disordered state. These ions are weakly bound in large tunnels along 〈111〉 and are mobile along them three-dimensionally.The presence of two alkaline cations in these tunnels is in favour of the ordered state. Single-crystals of K₈Na₄Sb₁₂O₃₆ are obtained and crystallize in the space group Pn3, $\text{a}\text{= 9,515(3)}\text{A}\text{?}$. Using 563 independent reflections, the structure has been refined by full-matrix least squares, to factor R = 0,059.The comparison of the ionic conductivity of ordered (Pn3) and disordered (Im3) compounds is studied by the authors.     

Un nouveau conducteur protonique [H(H2O)n]12Sb12O36 (n ⩽ 1)

Single crystals of K₁₄Sb₁₂O₃₆F₂ undergo rapid ion exchange in 9N sulfuric acid to produce “hydronium” compound (H(H₂O)_n)₁₂Sb₁₂O₃₆ (n ? 1). Between 30 and 140°C this phase undergoes a partial and reversible dehydratation in which approximately 85 % of its “H₃O⁺” content is converted to H⁺.The structures of hydrated and dehydrated phases have been refined by full-matrix least squares, respectively to factor R = 0.030 and 0.047. The conductivity of $\text{(H(H}{}_2\text{O)}{}_{\mathrm{<mtext>n</mtext>}}\text{)}{}_{12}\text{Sb}{}_{12}\text{O}{}_{36}\text{(σ}{}_{20}\text{? 1O}{}^7\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$) increases in an Arrhenius relationship with an activation energy of 8.8 kcal.mole^?1, the dehydrated compound (H(H₂O)_0.33)₁₂Sb₁₂O₃₆ has a much lower conductivity but the same activation energy.     

Structure and lithium ion conductivity of garnet-like Li5La3Sb2O12 and Li6SrLa2Sb2O12

Oxides with the nominal chemical compositions Li₅La₃Sb₂O₁₂ and Li₆SrLa₂Sb₂O₁₂ were prepared by solid-state reaction. The structures were refined by the Rietveld method using powder X-ray diffraction data. The synthesis of Li₅La₃Sb₂O₁₂ resulted in the well known garnet-related structure plus 5 wt.% of La₂LiSbO₆ in the bulk. In contrast to that, Li₆SrLa₂Sb₂O₁₂ could be synthesised in single garnet-related type phase. Lithium ion conductivities of Li₅La₃Sb₂O₁₂ and Li₆SrLa₂Sb₂O₁₂ were studied by the ac impedance method. The grain-boundary contribution to the total (bulk + grain-boundary) resistance is very small and about 5 and 3% for Li₅La₃Sb₂O₁₂ and Li₆SrLa₂Sb₂O₁₂, respectively, at 24 °C and decreases further with increase in temperature. Among the investigated compounds, Li₅La₃Sb₂O₁₂ exhibits the highest total (bulk + grain-boundary) and bulk ionic conductivity of 7.8 × 10⁻⁶ and 8.2 × 10⁻⁶ S cm⁻¹, respectively, at 24 °C. The structural data indicate that the coupled substitution Li + Sr ⇒ La leads to a closure of the bottle neck like O-O distances of the shared edges of neighbouring Li octahedra and therefore reduces the mobility of Li ions in Li₆SrLa₂Sb₂O₁₂. Scanning electron microscope (SEM) images of the Li₆SrLa₂Sb₂O₁₂ compound revealed well crystallised large homogeneous grains (∼4.8 μm) and the grains were in good contact with the neighbouring grain, which leads to a smaller grain-boundary contribution to the total resistance.     

Synthesis and structural characterization of Eu(III)-doped Zn7Sb2O12

In addition to the lanthanide series elements, Europium is one of the chemical elements of greatest interest for the development of species with oxidation state +3 (III), which leads to interesting electronic transitions. In a general sense, their emission spectrum lines are narrow and sensitive to effects of the ligand field around metallic ions. This property allows the use of Eu(III) as a structural probe. In this work, samples of semiconductor Zn₇Sb₂O₁₂ and of solid solutions based on isoelectronically Eu(III)-doped Zn₇Sb₂O₁₂ with stoichiometry Zn_7−3x Eu_2x Sb₂O₁₂ were prepared. Both Zn₇Sb₂O₁₂ and Zn_7−3x Eu_2x Sb₂O₁₂ were synthesized via a chemical route using Pechini’s method and characterized by Fourier transform infrared absorption vibrational spectroscopy (FTIR) and photoluminescence spectroscopy. In order to perform further spectral analyses, each spectrum was adjusted using a set of Gaussian functions. The FTIR spectrum analysis showed a slight band shift of the vibration mode assigned to the Sb–O bonding ascribed to the [SbO₆] octahedron vibration. The theoretical fitting of the luminescence curves showed a broadening of the most intense emission peaks related to the transition Eu(III) ⁵D₀ → ⁷F₂. As a whole, the results suggest that a less symmetric Eu(III) site occupation in inverse spinel structure may occur in sites close to the antimony octahedron, involving, however, non-substitutional site occupation.     

Improved luminescence from Y2Sn2O7:Tb nanoparticles co-doped with Sb ions

Very small nanoparticles (size 3-5 nm) of Y₂Sn₂O₇, Y₂Sn₂O₇:Tb³⁺ and Sb³⁺ co-doped Y₂Sn₂O₇:Tb³⁺ were prepared at a relatively low temperature of 700 °C. Y₂Sn₂O₇ host is characterised by an emission around 436 nm, which is arising from the oxygen vacancies present in the lattice. Tb³⁺ emission improves significantly when Sb³⁺ ions are co-doped with Y₂Sn₂O₇:Tb³⁺ nanoparticles. Incorporation of Sb³⁺ ions at the Y³⁺ site of Y₂Sn₂O₇ lattice and associated lattice distortion around Tb³⁺/Y³⁺ ions brought about by the difference in the stable coordination number of Sb³⁺ and Y³⁺ ions are responsible for the improved Tb³⁺ emission from the co-doped samples.     

Irradiation induced texturing in the Mg0.95Mn0.05Fe2O4 ferrite thin film

We present a study on the effect of swift heavy ions irradiation on the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ ferrite thin film grown by pulsed laser deposition technique. X-ray diffraction (XRD) pattern of the as-deposited film reveals a cubic spinel structure with an intermediate phase of α-Fe₂O₃. This impurity phase completely dissolves upon irradiation with 200 MeV Ag¹⁵⁺-ions and it exhibits a strong crystallographic texture along the (440) plane. The magnetization values start increasing systematically with irradiation at lower fluence values, whereas decrease for higher one. This decrease in magnetic signal can be attributed to partial amorphization caused by irradiation in agreement with XRD and atomic/magnetic force microscopic images.     

Etude des solutions solides entre le sesquioxyde de fer cubique γ-Fe2O3 et le ferrite de zinc ZnFe2O4

The authors have prepared metastable solid solutions between cubic iron sesquioxide γ-Fe₂O₃ and zinc ferrite ZnFe₂O₄. They give the main characteristics of these defect spinels. Fe³⁺ ions and vacancies are replaced by Zn²⁺ ions on tetrahedral sites. The lattice parameter and the thermal stability increase with the substitution rate. The magnetic behavior is comparable to that observed for solid solutions M_1?yZn_yFe₂O₄.     

Les composes Ag7AsS6 et Ag7AsSe6 etude des proprietes thermiques,cristallographiques et electriques

The preparation and the partial phase diagrams Ag₂X“As₂X₅” (X = S or Se) are described. Peritectic decompositions occur at 560°C for Ag₇AsS₆ and 360°C for Ag₇AsSe₆. Phase changes are observed at 250°C for Ag₇AsS₆ and 150°C for Ag₇AsSe₆. For each compound, the low temperature form is cubic P2₁3, and the high temperature form has the Ag₈GeTe₆ structural type, F$\text{4}$3m. The high temperature forms are not quenchable. Ionic and electronic conductivity have been measured in Ag₇AsS₆ and Ag₇AsSe₆. Ionic conductivity was measured using RbAg₄I₅ as a blocking electrode for electronic conduction. Electromotive force measurements confirm transference numbers. At room temperature, ionic conductivities were 1,5.10^?6 (Ω.cm)^?1 and 0,08 (Ω.cm)^?1 for Ag₇AsS₆ and Ag₇AsSe₆ respectively.     

Structural characterization of the lithiated iron oxides LixFe3O4 and LixFe2O3 (0<x<2)

Lithium has been inserted into Fe₃O₄ and α-Fe₂O₃ at room temperature both chemically and electrochemically; a compositional range 0<x<2 has been established for both Li_xFe₃O₄ and Li_xFe₂O₃. Powder X-ray-diffraction data of Li_1.5Fe₃O₄ indicate that the [Fe₂]O₄ subarray of the spinel structure remains intact; the A-site Fe³⁺ ions are displaced to empty octahedral positions and the Li⁺ ions in excess of x = 1 are located in tetrahedral sites. Lithiation of α-Fe₂O₃ causes the anion array to transform from hexagonal to cubic close packing; in this case the Li⁺ ions are distributed over both 16c and 16d octahedral sites of the cubic space group Fd3m.     

Structure, infrared and Raman spectroscopic studies of new Sr0.50SbFe(PO4)3 and SrSb0.50Fe1.50(PO4)3 Nasicon phases

Two newly synthesised Sr_0.50SbFe(PO₄)₃ [Sr_0.5.] and SrSb_0.50Fe_1.50(PO₄)₃ [Sr.] phases were obtained by conventional solid-state reaction techniques at 1000 °C in air atmosphere. Their crystallographic structures were determined at room temperature from X-ray powder diffraction (XRPD) data using the Rietveld analysis. Both compounds belong to the Nasicon structural family. [Sr_0.5.] and [Sr.] crystallise in rhombohedral system with \textR[`3] {\text{R}}\overline{3} and \textR[`3] \textc {\text{R}}\overline{3} {\text{c}} space group, respectively. Hexagonal cell parameters for [Sr_0.5.] and [Sr.] are: a = 8.227(1) ?, c = 22.767(2) ? and a = 8.339(1) ?, c = 22.704(2) ?, respectively. Sr²⁺ and vacancies in {[Sr_0.50]_3a[□_0.50]_3b}_M1SbFe(PO₄)₃ are practically ordered within the two positions, 3a and 3b, of M1 sites. Structure refinements show also an ordered distribution of Sb⁵⁺ and Fe³⁺ ions within the Nasicon framework. Within the structure, each Sr_(3a)O₆ octahedron shares two faces with two Fe³⁺O₆ octahedra and each vacancy (□_(3b)O₆) site is located between two Sb⁵⁺O₆ octahedra. In [Sr]_M1Sb_0.50Fe_1.50(PO₄)₃ compound, all M1 sites are occupied by Sr²⁺ and the Sb⁵⁺ and Fe³⁺ ions are randomly distributed within the Nasicon framework. A Raman and infrared spectroscopic study was used to obtain further structural information about the nature of bonding in both selected compositions.     

Cluster formation in Ag2O-P2O5-CdCl2 glass system

Ag₂O-P₂O₅ and Ag₂O-P₂O₅-20 wt% CdCl₂ glasses were prepared by melt quenching method and characterized with the help of several experimental techniques. Powder X-ray diffraction study indicated that the glasses are amorphous in nature. DSC studies showed that CdCl₂ doped glass is chemically more durable. Electrical conductivity and ionic transference number measurements have shown that both the glasses are ionic conductors with Ag⁺ ions as the charge carriers. The electrical conductivity of the doped glass is found to be higher than the undoped one. Structures of the glasses have been proposed on the basis of IR spectral analysis. From SEM studies it has been inferred that addition of 20 wt% CdCl₂ modifies the morphology of Ag₂O-P₂O₅ glass and in its presence formation of clusters composed of nanofibers occur.     

Zur kristallstruktur von (NH4)3Ti(O2)F5

The disordered ligand positions in (NH₄)₃Ti(O₂)F₅ (cubic, space group Fm3m - O⁵_h'$\text{a}\text{= 9.23}{}_2\text{A}\text{?}$) has been studied by X-ray single crystal investigation. A 3-dimensional fourier synthesis indicates a distribution of the disordered O-Atoms on the 96j positions (Oyz) similar to (NH₄)₃ZrF₇ where a pentagonal bipyramide has been proposed for geometrie of the ZrF₇-group. Due to the short O-O distance the structure of (NH₄)₃Ti(O₂)F₅ is better described as elpasolite where one of the six octahedral ligand positions are statistically replaced by an ‘edge on’ O^2?₂-group oriented there in two possible directions.     

Synthesis of Sb2O3 nanorods under hydrothermal conditions

Sb₂O₃ nanorods were successfully prepared via a mild hydrothermal route based on the reactions between SbCl₃ and NH₃·H₂O in aqueous solution at 120-180 °C for 12 h. The as-prepared Sb₂O₃ nanorods were characterized by X-ray diffraction (XRD), transmission electronic microscopy (TEM), and X-ray photoelctron spectroscopy (XPS). Results showed that NH₃·H₂O played a significant role in the formation of Sb₂O₃ nanorods. The presence of NH₃·H₂O could greatly favor the reaction progress toward the right-hand side and led to the orientation growth of Sb₂O₃ nanorods. A possible mechanism for the formation of Sb₂O₃ nanocrystallites was discussed.     

Conductivite anionique des phases du systeme PbF2 | SbF3

A solid solution Pb_1?xSb_xF_2+x (0 < x ≤ 0.40) of fluorite type and a definite Pb₂Sb₃F₁₃ phase have been obtained at 250°C in the PbF₂|SbF₃ system. The study of the variation of the ionic conduction shows that Pb_0.75Sb_0.25F_2.25 is a good ionic conductor.     

Structural transition induced by the release of residual stress in the complex of cubic and monoclinic Gd2O3:Eu nanoparticles

The Photoluminescence (PL) spectra of Gd₂O₃:Eu composed of cubic and monoclinic structure were collected on November 2003 and June 2006, respectively. The results show that a portion of cubic Gd₂O₃ transforms into monoclinic after the sample was left as it is for two years; and the ⁵D₁-⁷F_J emission of Eu³⁺ in cubic host was enhanced in this released complex. Considering the high pressure behavior of Gd₂O₃, we think this structural transition is due to the sample that endures a process of press and release while the residual stress is released slowly.     

Glass formation tendency in the system SeO2-Ag2O-B2O3

The glass formation regions in the system SeO₂-Ag₂O-B₂O₃ have been determined using the melt quenching method of evacuated silica ampoules. The structural units forming the amorphous network have been established by IR spectroscopy. The presence of SeO₃ (ν = 820 cm⁻¹; 760-750 cm⁻¹), BO₃ (ν = 1340, 1270 cm⁻¹) and BO₄ (ν = 1050 cm⁻¹) units has been confirmed. Crystallization of Ag₂SeO₃ only has been observed in a wide concentrate region near the glass formation boundary. A model explaining the unsatisfactory glass formation ability in the system investigated has been developed. It has been suggested that Ag⁺ ions are predominantly located near the selenite units, which stimulates the formation of isolated SeO₃ groups. The transformation of BO₃ into BO₄ units is hindered by the absence of free Ag⁺ ions near the borate units.     

Synthesis and characterisation of the garnet-related Li ion conductor, Li5Nd3Sb2O12

In this paper the synthesis, conductivity, and structure of the garnet-related Li ion conductor, Li₅Nd₃Sb₂O₁₂, are reported. As for the related Li₅La₃M₂O₁₂ (M = Nb, Ta) materials, this phase shows high Li ion conductivity, with a conductivity at 300 °C of 9.2 × 10⁻³ S cm⁻¹. Structural studies using neutron diffraction indicate a cubic unit cell, space group Ia-3d, with Li located in two partially occupied sites. One of the sites is the traditional garnet structure tetrahedral site, while the other Li site is considerably more distorted. Although the latter is nominally a six coordinate site, a close inspection suggests that the coordination could be described as distorted tetrahedral, with the remaining two bonds being significantly longer (≈2.6 Å).     

Les phases SrLa2Al2O7 et SrGd2Al2O7

SrLa₂Al₂O₇ and SrGd₂Al₂O₇ belong to the structural type Sr₃Ti₂O₇. In SrGd₂Al₂O₇ strontium and gadolinium occupy respectively the 12 and 9 coordinated sites, whereas in SrLa₂Al₂O₇ the homologous cations are statistically distributed. The fluorescence spectra of both phases activated by Eu³⁺ ions show that the only possible position of Eu³⁺ is the 9 coordinated site.     

Effects of gamma-irradiation on Al2O3 crystals grown under reducing atmosphere

Gamma-ray irradiation-induced color centers in Al₂O₃ crystals grown by temperature gradient techniques (TGT) under a strongly reducing atmosphere were studied. The transition F⁺ → F takes place during the irradiation process. Glow discharge mass spectroscopy (GDMS) and annealing treatments show that Fe³⁺ impurity ions are present in the crystals. A composite (F⁺-Fe³⁺) defect was presented to explain the origin of the 255 nm band absorption in the TGT-Al₂O₃ crystals.     

Fabrication of Co3O4 cubic nanoframes: Facet-preferential chemical etching of Fe ions to Co3O4 nanocubes

The novel Co₃O₄ cubic nanoframes, sized in ca. 30 nm, were firstly fabricated via a facile solvothermal route. Based on the transmission electron microscopy and the powder X-ray diffraction analyses of the time-dependent products, a mechanism of facet-preferential chemical etching of Fe³⁺ ions to the pre-synthesized Co₃O₄ nanocubes is proposed for the formation of Co₃O₄ cubic nanoframes. This synthetic strategy can probably be extended to fabricate nanoframes of some other binary metal oxides, by designing similar chemical etching process.