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The crystal structure of rubidium–ammonium hexachlorotellurate [Rb0.8(NH4)0.2]2TeCl6, has been determined by X-ray single crystal analysis at room and low temperatures (260 K). The space group at both temperatures is Fm&3macr;m with a≈10.2 Å, Z=4. The refinement converged, at room and low temperatures to R=0.021 and 0.011, respectively. The title compound has an antifluorite-type arrangement of NH4+/Rb+ and octahedral TeCl62- anions. At room temperature, the H atoms belonging to ammonium group exhibit a six-fold disorder about [1 1 1]. Decreasing of temperature induces an ordering of NH4+, evidenced by a three-fold H-disorder and a decreasing of the equivalent thermal values. IR and Raman spectroscopic studies at room temperature were performed to confirm results of the X-ray diffraction. [Copyright &y& Elsevier]

In this study, calcined ZrTe 3 O 8 powder mixed with 7%wt of CuO was sintered at 750 °C. The new doped ceramic ZrTe 3 O 8 :7%CuO was synthesized using solid state reaction method and was studied with X-ray diffraction (XRD). At room temperature, the title compound crystallizes in cubic space group Ia 3 ‾ , with lattice parameter a = 11.328(3) Å, and exhibits a complex network of interconnected closed chains built up of TeO 4 E (E = electronic lone pair of Te (IV) atoms). The Zr/CuO 6 octahedra are inserted into these chains ensuring the stability of the structure by Zr/Cu –O–Te bonding contacts. IR and Raman spectroscopic study are employed as means to obtain preliminary structural information and confirms the presence of the ZrO 6 and TeO 4 E groups. Optical properties of the ceramic were explored by using UV–Vis absorption. The magnetic results reveal the appearance of a weak ferromagnetic behavior at low temperature (T C = 46.172 K). In addition, dielectric data were analyzed using real and imaginary permittivity ε ' and ε " respectively, the tan (δ) and the electrical modulus ( M ' and M″) for the sample ZrTe 3 O 8 :7%CuO at various frequencies. The Z ' and Z " versus frequency plots are well fitted to an equivalent circuit model composed of a series combination of two parallel combinations of resistance Ri and constant phase element CPEi. • The ceramic crystallized ain the cubic fluorite structure (Ia 3 ‾). • The Zr/CuO 6 octahedra are inserted into TeO 4 E chains ensuring the stability of the structure by Zr/Cu –O–Te bonding contacts. • The magnetic results reveal the appearance of a weak ferromagnetic behavior at low temperature (T C = 46.172 K). • The equivalent circuit model is composed of a series combination of two parallel combinations of resistance Ri and constant phase element CPEi. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure of the new Li-doped material [Li0.08(NH4)0.92]2TeCl4Br2, has been determined by X-ray single crystal analysis at room temperature. The title compound crystallizes in the tetragonal space group P4/mnc, with a lattice parameters a =7.3269(3)Å and c =10.3916(5)Å, Z =2. The structure of [Li0.08(NH4)0.92]2TeCl4Br2 consists of isolated TeCl4Br2 octahedra slightly deformed in c-direction. These octahedra show a slightly rotation around the fourfold axis against the cubic arrangement of the K2PtCl6 type structure. The monovalent cations are located between the octahedra ensuring the stability of the structure by ionic and hydrogen bonding contacts: Li⋯Cl/Br and N–H⋯Cl/Br. Three endothermic peaks in thermal behavior were detected for this compound at 350K, 419K and 558K, by DSC experiment. The first transition was confirmed by Raman spectroscopic and IR studies. Hydrogen bonding, the nature and the degree of structure (dis)order and the mechanisms of the transitions are discussed. The dielectric constant at different frequencies and temperatures revealed a phase transition at 350K related to reorientation and H+ diffusion. [ABSTRACT FROM AUTHOR]

A glass-forming domain was evidenced and studied within the TeO 2 TiO 2 ZnO system. Density, glass transition temperature ( T g ) and onset crystallization temperature ( T 0 ) were measured and interpreted as a function of the zinc oxide mole fraction for relevant glasses. It was concluded that the zinc oxide favors the thermal stability of glasses. On the other hand, the impact of TiO 2 addition is even more pronounced on the enhancement of the thermal stability. The optical transmission was recorded for series of glasses in the UV–Visible–NIR range. Refractive index and optical band gap were extracted from these measurements and studied as a function of the ZnO content. Linear refractive indices and optical band gap were found to decrease and increase respectively, with increasing ZnO content. The third-order non-linear susceptibility Re ( χ 3 ), measured for two series of glasses (TiO 2 content was fixed either to 5 or 10 mol%), was found to progressively decrease when the ZnO concentration increases. The impact of ZnO modifier on the glass structure was discussed based on Raman spectroscopy data. We evidenced that TiO 2 does not change drastically the glass network, whereas ZnO leads in a first step to the breaking of the Te O Te bridges, inducing network depolymerization. A further addition in ZnO leads to the formation of new Te O Zn and Zn O Zn linkages. [ABSTRACT FROM AUTHOR]

Stable glasses are successfully synthesized in the TeO 2 -GeO 2 -ZnO system at 850 °C by the melt-quenching method and the glass forming domain is determined in the TeO 2 -rich part of the diagram. The thermal study, carried out using differential scanning calorimetry, reveals that the glass transition temperature, as well as the thermal stability, increases with the addition of ZnO or GeO 2 . Bulk glass samples are elaborated within two series of compositions, corresponding to fixed concentrations in GeO 2 (respectively 5 or 10 mol. %), and to various contents in ZnO. Structural changes caused by the ZnO addition are discussed based on Raman spectroscopy data. A progressive but very moderate network depolymerization is shown with increasing amount of ZnO. However, two different regimes can be identified, depending on the ZnO content. It is believed that ZnO acts as a network modifier for compositions below 20 mol. %, and starts to participate as a glass network former over such concentration. It is well evidenced that GeO 2 contributes to the increase in Young's modulus E , evaluated from ultrasonic echography measurements. In addition, this oxide favors the network reticulation detected by the decrease of the Poisson ratio and the increase of the fractal bond connectivity. However, the role of ZnO is more complicated and will be extensively discussed. The decrease in the atomic packing density C g probably explains the global evolution of E as a function of ZnO content. The refractive indices and optical band gap energies are extracted from UV-Visible-NIR optical transmission data. For the studied glasses, it is found that the transmission threshold decreases with larger ZnO contents, reflecting the increase in the optical band gap value. Refractive index is finally seen to decrease as a function of both ZnO and GeO 2 contents. Such variation is explained by the decrease of the molar electronic polarizability, and by the lower optical basicity values known for TeO 3 entities in comparison to TeO 4 units. [ABSTRACT FROM AUTHOR]