Luminescence properties of monoclinic Cu4I4(Piperidine)4

A new modification of Cu₄I₄Pip₄ has been synthesized under hydrothermal conditions. X-ray crystallography revealed that this compound crystallized in the monoclinic system and consists of a tetrahedral core with composition Cu₄I₄, in which each Cu atom is coordinated by a piperidine molecule via the N atom. In contrast to a previously reported modification of Cu₄I₄Pip₄, the present modification shows luminescent properties when exposed to UV-light. In addition, we have used time-dependent density functional theory calculations to characterize both compounds in term of both absorption and emission.     

The oxygen defect perovskite BaLa4Cu5O13.4, a metallic conductor

A new oxygen defect perovskite BaLa₄Cu₅O_13.4, characterized by a mixed valence of copper has been isolated; the parameters of the tetragonal cell are closely related to that of the cubic perovskite:a = 8.644(4)$\text{A}\text{?}\text{=}\text{a}{}_{\mathrm{p}}\text{5√}$ and c = 3.867(3) $\text{A}\text{?}\text{=}\text{a}{}_{\mathrm{p}}$. The X-ray diffraction study shows that the atoms are displaced from their ideal positions in the cubic cell, owing to the presence of ordered oxygen vacancies. The study of conductivity, magnetic susceptibility and thermoelectric power versus temperature shows that this oxide is a very good metallic conductor.     

Preparation and microstructure of nanocrystalline Rb0.5Cs0.5Ag4I5 thin films on NaCl substrates

Nanocrystalline Rb_0.5Cs_0.5Ag₄I₅ thin films were prepared by vacuum thermal evaporation on NaCl single crystal substrates. The microstructure and the electronic energy states of the thin films were examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The results showed that the obtained Rb_0.5Cs_0.5Ag₄I₅ layer has an epitaxial orientation relationship with the NaCl substrate, and the unit cell of nanocrystalline grain Rb_0.5Cs_0.5Ag₄I₅ thin films belongs to cubic crystal system. The principal X-ray diffraction peaks at d=3.7666, 3.4557, 3.3759, 2.3026, 2.1839, 2.1385, 1.9968, and 1.9624 Å are probably related to new quaternary compound Rb_0.5Cs_0.5Ag₄I₅ thin films structure. Based on which, it can be approximately concluded that the lattice constant is a=11.31 Å.     

Preparation and characterization of dense sodium superionic conducting Na5YSi4O12 (NYS)

Na₅YSi₄O₁₂ has been prepared from spray-frozen/freeze-dried precursor powders calcined at 620°C for three hours. Sintering at 1140°C for 30 minutes gave a ceramic of 97.7% theoretical density. The material was single phase NYS with a 300°C resistivity of 6.5 Ωcm, an activation energy for Na⁺ ion conduction of 20.1 kJ/mol, a flexural strength of 75 MPa, a duplex fine grain structure of (0.1–3μm) and a constant linear thermal expansion coefficient (25–470°C) of 13.1 × 10^?6/°C ±5%. The properties of the NYS ceramics are especially sensitive to small soda deficiencies.     

Synthesis and crystal structure of the inter-alkali metal iodide Cs2Li3I5

Cs₂Li₃I₅ was obtained from the reaction of CsI, Li and I₂ in a sealed tantalum tube and colorless single crystals grown from the melt by slow cooling. This first inter-alkali metal iodide crystallizes in the monoclinic crystal system (C2/m, Z= 2) with a= 1666.8(6), b= 472.1(1), c= 1098.7(4) pm, β= 115.73(3)°. As the result of a x-ray crystallographic structure determination (R= 0.069, R_W= 0.066), Li⁺ is surrounded tetrahedrally (two thirds) and octahedrally (one third) by iodide. Cornersharing double chains of [LiI₄] tetrahedra are connected with edge-sharing chains of [LiI₆] octahedra to a layer of the composition [Li₃I₅]. Bicapped trigonal prisms [CsI₃] share faces and edges so that a network of the composition [Cs₂I₅] is formed which contains the necessary tetrahedral and octahedral holes for Li⁺.     

Glass formation and properties of GeSe2-Ga2Se3-MX (MX is alkali halide) chalcohalide glasses

The glass forming, optical, thermal, and mechanical properties of GeSe₂-Ga₂Se₃-MX (MX is alkali halide) chalcohalide glasses are reported. A unique property of the glasses is that they have excellent transparency in red-light region in addition to the 8-14 μm atmospheric window. This property is interesting and important for improving the quality control of infrared systems. These glasses also present good thermal stability. They could be promising materials for infrared transmitting applications, although their thermo-mechanical properties are relatively weak.     

Electrical conductivity of the systems (Rb4−xMx)Cu16I7Cl13 (M=K,Cs), Rb4Cu16(I7−xBrx)Cl13 and Rb4Cu16I7(Cl13−xBrx)

The solid solution ranges in the systems (Rb_4?xK_x)Cu₁₆I₇Cl₁₃, (Rb_4?xCs_x)Cu₁₆I₇Cl₁₃, Rb₄Cu₁₆(I_7?xBr_x)Cl₁₃, and Rb₄Cu₁₆I₇(Cl_13?xBr_x), have been examined and the electrical conductivity has been measured as a function of temperature and composition. In the system (Rb_4?xK_x)Cu₁₆I₇Cl₁₃, room temperature conductivities increase from 0.32Scm^?1 for x=0 to 0.47Scm^?1 for x=0.40. On the other hand, the conductivities of the systems (Rb_4?xCs_x)Cu₁₆I₇Cl₁₃ and Rb₄Cu₁₆I₇(Cl_13?xBr_x) decrease with increasing x. The system Rb₄Cu₁₆(I_7?xBr_x)Cl₁₃ shows no significant change of the conductivity on x.     

The possibility of intercalating alkali metals in a glass of the system V2O5 - P2O5

A semi-conducting phosphovanadate glass was tested as a possible material for positive electrode in solid state batteries.O.c. voltage with alkali metal (3.6 V/Li and 3.4 V/Na) is higher than for crystallized vanadium oxides and chemical intercalation of sodium or lithium is obtained using halogenated salts dissolved in organic solvents.     

Composition dependence of infrared edge absorption in ZrF4 and HfF4 based glasses

A set of semi-empirical criteria have been developed to assess the contribution of various components to IR edge absorption in multi-component solids. These have been applied to ZrF₄ and HfF₄ based glasses and verified experimentally. Results indicate that monovalent cation fluorides no lighter than NaF, divalent cation fluorides no lighter than CaF₂, trivalent cation fluorides no lighter than LaF₃ and quadrivalent cation fluorides no lighter than ThF₄ contribute negligibly to IR edge absorption in such glasses.     

On the proton conductor (H3O)Zr2(PO4)3

The compound HZr₂(PO₄)₃ was converted to (H₃O)Zr₂(PO₄)₃ by refluxing in water for 12 or more hours. The water is lost above 150°C to regenerate the original triphosphate. The hydronium ion phase is rhombohedral with hexagonal axes of a = 8.760(1) and $\text{c}\text{= 23.774(4)}\text{A}\text{?}$. Proton conduction in these compounds was investigated by an ac impedance method over the frequency range 5Hz – 10MHz. The activation energy for (H₃O)Zr₂(PO₄)₃ in the temperature range of 25 to 150°C was 0.56eV while the corresponding value for HZr₂(PO₄)₃ (125 – 300°C) was 0.44eV.     

Preparation and structural properties of the solid state ionic conductor CuTi2 (PO4)3

The solid state ionic conductor CuTi₂(PO₄)₃ belonging to the Nasicon family has been synthesized; its lattice parameters have been obtained from X-ray diffraction patterns by comparison with isostructural NaTi₂(PO₄)₃. The characterization of this light brown solid has been completed by IR and UV-visible spectroscopies. Reverse ion exchange between Cu and Na has been shown to occur in a molten salt bath. These properties are discussed through the main structural features of the M^IM′^IV₂(PO₄)₃ family.     

Lithium ion conduction in Li5A104, Li5GaO4 and Li6ZnO4

Polycrystalline samples of Li₅Al0₄, Li₅Ga0₄, and Li₆Zn0₄ have been synthesized, and their ionic conductivity measured over a range of temperature. These materials, which have the antifluorite structure with large concentrations of intrinsic cation vacancies, have Arrhenius-like conductivities at low temperatures, with a steep rise in the range 385–450°C, reaching very high values, with a very small temperature dependence, thereafter. Materials of this type, which exhibit the highest values of lithium ion conductivity yet found, may have important practical applications in devices such as elevated temperature batteries.     

Formation and properties of glasses in the CaF2AlF3P2O5 system

Glasses from the system CaF₂AlF₃P₂O₅ have been synthesized. Glass formation characteristics, thermal expansion, and optical transmission of these glasses in the visible and infrared regions are described. Incorporation of P₂O₅ in the system greatly suppressed the spontaneous crystallization tendencies of the CaF₂AlF₃ binary system. The glasses obtained from the system transmit in the mid-infrared range. A strong absorption band centerd at 4.8 microns is a characteristic of these glasses. The absorption band is related to the presence of P₂O₅ in the glass.     

Stability of the dry proton conductor CsHSO4 in hydrogen atmosphere

With an objective to assess the suitability of the dry proton conductor cesium hydrogen sulfate (CsHSO₄) as an electrolyte for fuel cells, its chemical stability in H₂ atmosphere in presence of the electrocatalyst Pt/C has been investigated. X-ray diffraction and differential scanning calorimetric (DSC) data indicate that CsHSO₄ decomposes to Cs₂SO₄ and H₂S at 150 °C in H₂ atmosphere when it is mixed with Pt/C catalyst, while it is quite stable under identical conditions in the absence of the Pt/C catalyst. Although thin composite membranes (∼80 μm) prepared with poly(vinylidene fluoride) and CsHSO₄ exhibit high proton conductivity at 150-200 °C that is adequate for fuel cell applications, development of compatible non-platinum alloy or transition metal oxide catalysts is needed before CsHSO₄ could be considered as an electrolyte for fuel cells. Also, processing procedures need to be optimized to obtain dense, gas impermeable membranes suitable for fuel cell applications.     

X-ray diffraction studies of glasses in the TeO2V2O5 system

The short-range order in glasses of the TeO₂V₂O₅ system is studied with the aid of X-ray diffraction. It is found that the main structural units in most of the glasses are VO₅- and TeO₃-groups. The assumption is made that their structures gradually change; sheet complexes are formed close to V₂O₅; chains - around 2TeO₂V₂O₅, and a tridimensional aperiodic network in glasses from TeO₂.     

Rb5Nd(MoO4)4 a self-tunable birefringent laser crystal

In this paper we report an experimental demonstration of broadband wavelength self-tuning in Rb₅Nd(MoO₄)₄ laser crystal (RNM) together with the theoretical treatment which explains the system behaviour based on its birefringent properties. The self-frequency tuning in RNM was obtained by inserting an a-cut plate inside the laser resonator close to the Brewster's angle. At a given position of the crystal plate, when the wavelength of the oscillating mode corresponds to an integral number of full-wave retardation in the plate, the laser operates in the p polarization of the Brewster surface with no losses. The experimental self-frequency tuning of the laser emission along the free spectral range of the RNM crystal (1062.94–1067.84 nm) was obtained by rotating the birefringent gain plate in its own plane. To investigate the tuning characteristics of the spectral filter, we have used the Jones-vector formalism. The calculated wavelength-selective tuning matches the experimental observations.     

Dissolution process of photodoped and melt-quenched AgGe20Se80 glasses in alkali solutions

The dissolution process in NaOH solutions was studied comparatively for photodoped and melt-quenched AgGe₂₀Se₈₀ glasses. A large difference in the dissolution rate was found between these glasses, and it was ascribed to the difference in the distribution of Ag atoms in the glasses. Moreover, from an analysis of the dissolution curves of the photodoped glasses, it was shown that the Ag-photodoping in Ge₂₀Se₈₀ glasses was a diffusion-controlled process, with an apparent diffusion coefficient of about 4.0 × 10^?11 cm²/sec at room temperature.     

Electronic characterization of alkali ruthenium hollandites: KRu4O8, RbRu4O8 and Cs0.8Li0.2Ru4O8

Transport, specific heat, and magnetic measurements have been performed on three alkali hollandites: KRu₄O₈, RbRu₄O₈, and a newly synthesized Cs analog, Cs_0.8Li_0.2Ru₄O₈, which was determined to have space group I4/m (#87) and lattice parameters, a = 10.0850(4) and c = 3.12180(20). In contrast to the ruthenium perovskites, which display a wide range of electrical and magnetic behavior, the alkali hollandites are simple paramagnetic metals.     

Sol-gel preparation and properties of TiO2-P2O5 bulk glasses

Monolithic transparent and colorless, or Ti³⁺-free TiO₂-P₂O₅ glasses containing very large amounts of TiO₂ (up to 93 mol%) were successfully prepared by heat-treating the xerogels, which were made from titanium tetraisopropoxide and triethyl phosphate, through the sol-gel reaction. The density and refractive index n_632.8 nm of the sol-gel-derived glasses were higher than the melt-derived glasses of the corresponding compositions. The glasses of TiO₂ content of larger than 80 mol% seemed somewhat porous, but n_632.8 nm of these glasses was very high as 2.2-2.3. Higher density and higher n_632.8 nm than the melt-derived glasses were considered to be due to more abundance of six-fold coordinated Ti⁴⁺ ions.     

Temperature shift of the optical gap in some PbO-ZnO-P2O5 glasses

The optical gap (E_g) between 4.54 eV-4.88 eV at room temperature was determined for PbO-ZnO-P₂O₅ glasses with the formal content of P₂O₅ in the region of 30 to 50 mol% and with the formal content of PbO in the region of 50 to 45 mol%, respectively. The temperature (T) dependence of the optical gap (E_g(T)) in the region 80 < T[K] < 600 was determined, and an electron-phonon interaction is suggested to be a major contribution to the temperature shift of the optical gap. In the temperature region of 300-600 K, the E_g(T) dependence can be approximated by a simple linear relation with the temperature coefficient (γ) of the optical gap in the region 6.04 ≤ γ × 10⁴ [eV/K] ≤ 7.39.