Thermal,vibrational and Ac impedance studies on proton conducting polymer electrolytes based on poly(vinyl acetate)

Proton conducting polymer electrolytes based on poly(vinyl acetate) (PVAc) and perchloric acid (HClO₄) have been prepared by solution casting technique with various compositions. The X-ray diffraction analysis confirms the polymer–HClO₄ complex formation. FTIR spectra analysis reveals the interaction between proton and ester oxygen of poly(vinyl acetate) (PVAc). The shift in T_g towards the lower temperature indicates that the polymer salt interaction takes places in the amorphous phase of the polymer matrix. Ac impedance spectroscopy reveals that 75 mol% PVAc:25 mol% HClO₄ exhibits maximum conductivity, 3.75 × 10^? 3 S cm^? 1 at room temperature (303 K). The increase in conductivity with increase in dopant concentration and temperature may be attributed to the enhanced mobility of the polymer chains, number of charge carriers and rotations of side chains. The temperature dependence of conductivity shows non-Arrhenius behavior at higher temperatures.     

Study of microstructure in Agx(As0.33Se0.67)100−x chalcogenide glasses

Glasses with general formula Ag_x(As_0.33Se_0.67)_100−x were studied by means of modulated differential scanning calorimetry (MDSC), conductivity and permittivity measurements and atomic force acoustic microscopy (AFAM). In the whole range of doping (x = 2–12 at.% Ag) a phase separation was supposed. The proportional amount of the ion-conductive Ag rich phase increased with the Ag content. A rapid increase (almost four orders of magnitude) in the conductivity was observed in the Ag concentration range 4–8 at.%, which could be associated with the interconnection of this ion-conductive phase. The transition from a hole conductivity (at low Ag concentration) to a mixed ionic-hole conductivity at higher Ag concentration was studied by permittivity measurements.     

Structural peculiarities, and electrical and optical properties of 70TeO2·30PbCl2 glasses doped with Pr, prepared in Pt or Au crucibles

The influence of crucibles (Au or Pt) on the structure, electrical, dielectric and optical properties of 70TeO₂·30PbCl₂ glasses doped with Pr³⁺ added as a metal, chloride, or oxide, in concentrations of 500–1500 wt-ppm, is reported. The dc conductivity of ‘pure’ glasses prepared in Au crucibles is two orders of magnitude higher than that of those prepared in Pt crucibles. Upon doping, the dc conductivity of glasses prepared in Pt and Au crucibles increases or decreases, respectively. The static relative permittivity is equal to 33 ± 2. In the range of 640–700 nm, six photoluminescence (PL) peaks were observed, at 641.5, 647.1, 652.4, 660.8, 662.9, and 664.5 nm. In the range of 200–1200 cm⁻¹, seven Raman scattering (RS) peaks were observed at 184, 217, 321, 468, 654, 735 cm⁻¹, and a small peak at 650 cm⁻¹. Both spectra were deconvoluted using symmetrical Gaussian functions. Relative intensities of PL and RS bands depend on the concentration and chemical form of Pr³⁺ and on the material of the crucible. However, positions of these bands are independent of these conditions.     

Electrical and dielectric properties of Sb2O3–V2O5–K2O glasses

Electric measurements, including temperature dependencies of direct electrical conductivity and temperature dependencies of complex electrical modulus, have been implemented using Sb₂O₃–V₂O₅–K₂O glass samples. These glasses absorb ambient humidity but their resistance to water attack depends on composition. The significant decrease of conductivity up to 100 °C can arise from water desorption. Cycling measurements of direct electrical conductivity versus temperature were also implemented. They show that the 30Sb₂O₃–30V₂O₅–40K₂O and 70Sb₂O₃–30K₂O glasses are irreversibly damaged with the formation of the hydrated layer. In addition, it was observed that the evolution of DC conductivity is ruled by Arrhenius relation, while activation energy decreases as Sb₂O₃ concentration increases.     

Optical and structural properties of Ge–Se bulk glasses and Ag–Ge–Se thin films

The optical and structural properties of Ge₂₀Se₈₀, Ge₂₅Se₇₅ and Ge₃₀Se₇₀ bulk glasses and Ag_x(Ge_0.20Se_0.80)_100−x thin films, where x = 0, 6, 11, 16, 20 and 23 at.% were studied. All samples were confirmed as amorphous according to XRD. The Raman spectra showed increase in 260 cm⁻¹ and 237 cm⁻¹ and decrease in 198 cm⁻¹ and 216 cm⁻¹ bands with different Se content in the bulk samples. The optical bandgap energy of bulk samples decreased (2.17–2.08 eV) and refractive index increased (2.389–2.426 at 1550 nm) with increasing Se content in bulk glasses. The Ge₂₀Se₈₀ thin films were prepared by vacuum thermal evaporation from Ge₃₀Se₇₀ bulk glasses. The Raman spectra of the films showed that peaks at 260 cm⁻¹ and 216 cm⁻¹ decreased their intensities with increasing Ag content in the thin films. The significant red shift of bandgap energy occurred upon different Ag content. The optically induced dissolution and diffusion resulted in graded refractive index profile along the film thickness caused by different Ag concentration. The refractive index increased from the substrate side to the top of thin films. The graded profile was getting more uniform with increasing content of silver in the thin film.     

Glass formation in the GexTe100−x binary system: Synthesis by twin roller quenching and co-thermal evaporation techniques

The Ge–Te system exhibits one main composition domain where glasses can be easily prepared by melt quenching technique; this domain is centered on the eutectic composition Ge₁₅Te₈₅. In this work, bulk flakes and films of composition Ge_xTe_100−x with x  50 at.% were prepared by two different quenching techniques: (i) the twin roller quenching for bulk flakes and, (ii) the co-thermal evaporation for films (with thickness comprised between 2 and 14 μm). Electron Probe Micro-Analysis was used to check the composition of the materials while X-ray diffraction allowed identifying the amorphous state and/or the crystalline phases present in the Ge_xTe_100−x samples. Thermal properties for both types of materials were investigated by differential scanning calorimetry. The glass-forming regions were: 11.7–22.0 at.% Ge for bulk flakes and 10.2–35.9 at.% Ge for films. A similar thermal behavior of bulk flakes and thick films was highlighted by Differential Scanning Calorimetry.     

Electro-optical characterization of Ge–Se–Te glasses

Chalcogenide bulk glasses Ge₂₀Se_80−xTe_x for x(0,15) have been prepared by systematic replacement of Se by Te. Selected glasses have been doped with Ho, Er and Pr, and samples have been characterized by transmission spectroscopy, measurements of dc electrical conductivity and low-temperature photoluminescence. Absorption coefficients have been derived from measured transmittance and estimated reflectance. Arrhenius plots of dc electrical conductivity, in the measured temperature range 300–460 K, are characterized by single activation energies roughly equal to the half of the optical gap. Activation energies deduced from Arrhenius plots reveal a systematic decrease with increasing Te content. Similarly, both absorption and low-temperature photoluminescence spectra reveal shifts of absorption edge and/or dominant luminescence band to longer wavelength due to Te → Se substitution. Samples doped with Ho and Er exhibit a strong luminescence at 1200 and 1540 nm due to ⁵I₆ → ⁵I₈ and ⁴I_13/2 → ⁴I_15/2 transitions of Ho³⁺ and Er³⁺ ions, respectively. Pr doped samples exhibit only a relatively weak luminescence peak at 1590 nm, which we tentatively assign to ³F₃ → ³H₄ transition of Pr³⁺ ions. Absorption of the base glass luminescence at 1460 and 1520 nm has been observed at low temperature on samples doped with Pr and Er, respectively.     

Rapid quenching and glass formation in chalcogenide glasses: Preparation and properties of Ge–As–Te glasses over an extended composition ranges

In Ge–As–Te system, the glass forming region determined by normal melt quenching method has two regions (GFR I and GFR II) separated by few compositions gap. With a simple laboratory built twin roller apparatus, we have succeeded in preparing Ge_7.5As_xTe_92.5−x glasses over extended composition ranges. A distinct change in T_g is observed at x = 40, exactly at which the separation of the glass forming regions occur indicating the changes in the connectivity and the rigidity of the structural network. The maximum observed in glass transition (T_g) at x = 55 corresponding to the average coordination number (Z_av) = 2.70 is an evidence for the shift of the rigidity percolation threshold (RPT) from Z_av = 2.40 as predicted by the recent theories. The glass forming tendency (K_gl) and ΔT (=T_c−T_g) is low for the glasses in the GFR I and high for the glasses in the GFR II.     

Low temperature dielectric dispersion and electrical conductivity studies on Fe2O3 mixed lithium yttrium silicate glasses

Lithium yttrium silicate glasses mixed with different concentrations of Fe₂O₃ of the composition (40 ? x) Li₂O–10Y₂O₃–50SiO₂: x Fe₂O₃, with x = 0.3, 0.5, 0.8, 1.0, 1.2 and 1.5 (all in mol%) were synthesized. Electrical and dielectric properties including dielectric constant, ε′(ω), loss, tan δ, ac conductivity, σ_ac, impedance spectra as well as electric moduli, M(ω), over a wide continuous frequency range of 40 Hz to 10⁶ Hz and in the low temperature range 100 to 360 K were measured as a function of the concentration of Fe₂O₃. The dc conductivity is also evaluated in the temperature range 100 … 360 K. The temperature and frequency dispersions of dielectric constant as well as dielectric loss have been analyzed using space charge polarization model. The ac and dc conductivities have exhibited increasing trend with increasing Fe₂O₃ content beyond 0.5 mol%, whereas the activation energy for the conductivity demonstrated decreasing tendency in this dopant concentration range. Both quantum mechanical tunneling (QMT) and correlated barrier hopping models (CBH) were used for clarification of ac conductivity origin and the corresponding analysis has indicated that CBH model is more appropriate for this glass system. For the better understanding of relaxation dynamics of the electrical properties we have drawn the scaling plots for ac conductivity and also electric moduli. The plots indicated that the relaxation dynamics is independent on temperature but depends on concentration of Fe₂O₃. The dc conductivity is analyzed using small polaron hoping model. The increase of conductivity with the concentration of Fe₂O₃ beyond 0.5 mol% is explained in terms of variations in the redox ratio of iron ions in the glass network. The results were further analyzed quantitatively with the support of experimental data from IR, optical absorption and ESR spectral studies. The overall analysis has indicated that Li₂O–Y₂O₃–SiO₂ glasses containing more than 0.5 mol% of Fe₂O₃ are more suitable for achieving good electrical conductivity in these glasses.     

Crystal growth, characterization and spectroscopic study of europium-doped NaY(PO3)4

Europium-doped NaY(PO₃)₄ single crystals have been synthesized by the flux method with sizes around 1 mm³. The unit cell parameters at room temperature refined by X-ray powder diffraction are a=7.1510(4) Å; b=13.0070(8) Å; c=9.6973(2) Å; β=90.606(3)°, Z=4 with the space group P2₁/n in monoclinic system. The present single crystals have a needle shape, they are elongated along the a crystallographic direction, and their size is in the 500 μm–1 mm range. The linear thermal expansion tensor parameters were determined, being the maximum value along the b direction, 16.1×10⁻⁶ K⁻¹ and the minimum along the a direction being 11.7×10⁻⁶ K⁻¹. The IR vibration modes attributed to the group P–O are consistent with the crystallographic data concerning the chain aspect of the phosphate anion. This material melts incongruently at 1141 K. Intense visible emissions attributed to Eu^{3+ 5}D₀→⁷F₁, ⁵D₀→⁷F₂ and ⁵D₀→⁷F₄, electronic transitions have been observed after pumping at 355 nm at room temperature.     

Synthesis,Characterisation and Magnetic Properties of a One-Dimensional Iron(II) Coordination Polymer

Abstract  

A new iron(II) coordination polymer, [FeCl₂(NC₇H₉)₂(N₂C₁₂H₁₂)], has been synthesized under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction. This material crystallizes in the monoclinic space group C2/c, with a = 11.2850(6), b = 13.8925(7), c = 17.0988(9) ? and β = 94.300(3)o (Z = 4). The crystal structure consists of neutral zig-zag chains, in which the iron(II) ions are octahedrally coordinated. The infinite polymer chains are packed into a three-dimensional structure through C–H···Cl interactions. Magnetic susceptibility measurements reveal the existence of weak antiferromagnetic interactions between the iron(II) ions. The effective magnetic moment, μ _eff = 5.33 μ _B , is consistent with a high-spin iron(II) configuration.     

Electrical properties of A2.6+xTi1.4−xCd(PO4)3.4−x (A = Li,K; x = 0.0–1.0) phosphate glasses

Electrical properties of A_2.6+xTi_1.4−xCd(PO₄)_3.4−x (A = Li, K; x = 0.0–1.0) phosphate glasses are investigated over a frequency range from 42 Hz to 1 MHz at different temperatures. Impedance spectroscopy is used to separate the bulk conductivity from electrode effect of electrical conductivity data. The bulk dc conductivity is Arrhenius activated, with activation energies and pre-exponential factors following the Meyer–Neldel rule. The real part of ac conductivity shows universal power law feature. The variation of dielectric constant with frequency is attributed to ion diffusion and polarization occurring in the phosphate glasses. The frequency dependent imaginary part of electric modulus M″(ω) plot shows non-Debye feature in conductivity relaxation. The Kohlrausch–Williams–Watts stretched exponential function was used to describe the modulus spectra and the stretching exponent β is found to be temperature independent. Scaling in M″(ω) shows that the electrical relaxation mechanisms are independent of temperature for given composition at different temperatures.     

Optical and electrical properties of as-prepared and annealed (Se80Te20)100 − xAgx (0 ≤ x ≤ 4) ultra-thin films

Optical and electrical properties of the (Se₈₀Te₂₀)_100 ? xAg_x (0 ≤ x ≤ 4) ultra-thin films have been studied. The ultra-thin films were prepared by thermal evaporation of the bulk samples. Thin films were annealed below glass transition temperature (328 K) and in between glass transition temperature and crystallization temperature (343 K). Thin films annealed at 343 K showed crystallization peaks for Se–Te–Ag phases in the XRD spectra. The transmission and reflection of as-prepared and annealed ultra-thin films were obtained in the 300–1100 nm spectral region. The optical band gap has been calculated from the transmission and reflection data. The refractive index has been calculated by the measured reflection data. It has been found that the optical band gap increases, but the refractive index, extinction coefficient, real and imaginary dielectric constant decrease with increase in Ag content. The optical band gap and refractive index show the variation in their values with increase in the annealing temperature. The extinction coefficient increases with increasing annealing temperature. The surface morphology of ultra-thin films has been determined using a scanning electron microscope (SEM). The measured dc conductivity, under a vacuum of 10^? 5 mbar, showed thermally activated conduction with single activation energy in the measured temperature range (288–358 K) and it followed Meyer–Neldel rule. The dc activation energy decreases with increase in Ag content in pristine and annealed films. The results have been analyzed on the bases of thermal annealing effects in the chalcogenide thin films.     

Glass formation in the MoO3–Nd2O3–La2O3–B2O3 system

In MoO₃–Nd₂O₃–B₂O₃ and MoO₃–Nd₂O₃–La₂O₃–B₂O₃ systems, glasses were obtained in the region between 20 and 30 mol% Ln₂O₃. A liquid-phase separation region was observed near the MoO₃–B₂O₃ side up to 20 mol% Ln₂O₃ (La, Nd). The amorphous phases were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), UV–VIS and infrared spectroscopy (IR). According to DTA data B₂O₃-rich glasses are stable up to 630 °C while glasses rich in MoO₃ are stable up to 430 °C. The glasses are transparent in the visible region. Structural models for the glasses network were suggested on the basis of IR spectral investigations. It was established that BO₃ (1380 cm⁻¹), BO₄ (1100–950 cm⁻¹) and MoO₄ (860 cm⁻¹) groups build up the glass network. MoO₆ units (band at 880 cm⁻¹) together with BO₃ units participate in the formation of the glass network with a high MoO₃ content (80–90 mol%).     

Structure, electrical, optical and thermal properties of Ge4Sb4Tex (x = 8, 9 and 10) thin films

The crystalline samples of Ge₄Sb₄Te₁₀, Ge₄Sb₄Te₉, and Ge₄Sb₄Te₈ were prepared and their amorphous semiconducting thin films obtained by flash evaporation. Their sheet resistance decreased slowly with temperature up to 147–160 °C with activation energy of electrical conductivity ΔE = 0.40–0.44 eV. Above these temperatures, the sheet resistance drops abruptly by several orders due to crystallization. The drop of resistivity proceeds in two steps. Two steps of phase change were also found on curves of DSC and on the temperature dependence of index of refraction. It pays for slow heating rates, crystallization induced by short (≈30 ns) laser pulses proceeds probably in one step only for all studied samples (as it follows from X-ray diffraction), not only for Ge₂Sb₂Te₅ in which a single phase formation was confirmed. The crystallization temperatures are increasing slightly with decreasing Te content in the series Ge₄Sb₄Te₁₀–Ge₄Sb₄Te₉–Ge₄Sb₄Te₈ from 147 to 160 °C. The X-ray diffractograms revealed that in laser crystallized samples can be found only cubic modification of Ge₂Sb₂Te₅ type (a = 0.6 nm), while the samples annealed (230 °C, 2 h) or annealed after the crystallization with laser pulse, contain also small amounts of hexagonal phase.     

Crystal structures of 4,11-pregnadiene-3,20-dione and 21-methyl-20-oxa-4-pregnene-3,20-dione

The structures of the title compounds were solved by direct methods and refined by anisotropic full-matrix least-squares methods. 4,11-Pregnadiene-3,20-dione, C₂₁H₂₈O₂(1) crystallizes in the monoclinic space groupP2₁ (Z=2). The unit cell parametersa, b, c (Å), and (°) were: 12.319(2), 7.700(2), 9.717(2), 109.41(2). TheA- andC-rings exhibit intermediate sofa-halfchair conformations. TheB-ring has a chair conformation and theD-ring assumes an intermediate envelope-half-chair conformation. The progesterone side chain has a typical conformation; the C16–C17–C20–O20 torsion angle is –15.1(4)°. 21-Methyl-20-oxa-4-pregnene-3,20-dione, C₂₁H₃₀O₃ (2) crystallizes in the orthorhombic space groupP2₁2₁2₁ (Z=4). The unit cell parametersa, b, c (Å) were: 12.926(2), 19.447(4), 7.313(1). The progesterone side chain has an unusual conformation; the C16–C17–C20–O20 torsion angle is 174.6(4)°. TheA-ring has a 1, 2-half-chair conformation, ringsB andC exhibit chair conformations and ringD is in a 13,14-half-chair conformation.     

Synthesis and Structure of [Fe<Subscript>3</Subscript>O(O<Subscript>2</Subscript>CCH<Subscript>2</Subscript>OMe)<Subscript>6</Subscript>(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>][FeCl<Subscript>4</Subscript>]

Abstract  The structure of [Fe₃O(O₂CCH₂OMe)₆(H₂O)₃][FeCl₄] · 2.5H₂O has been determined. The three iron atoms and the μ₃-oxo are coplanar. Each carboxylic ligand is bidentate and links two iron atoms in the cluster. The clusters are linked by intra-trimer hydrogen bonding to form a zigzag motif that forms sheets via hydrogen bonding involving disordered waters of hydration. The [FeCl₄]⁻ anion is intercalated between the hydrogen-bonded sheets. Crystal data: space group P2₁/n, a = 10.276(2), b = 22.793(5), c = 17.091(3) ?, β = 96.66(3)°, V = 3976(1) ?³, Z = 4, R = 0.0837, wR ₂ = 0.1836. Graphical Abstract  The structure of [Fe₃O(O₂CCH₂OMe)₆(H₂O)₃][FeCl₄] · 2.5H₂O has been determined in which the clusters are linked by intra-trimer hydrogen bonding to form a zigzag motif that forms sheets via hydrogen bonding involving disordered waters of hydration.      

Electronic transport properties of mixed transition metal ions doped borophosphate glasses

A series of borophosphate glasses in the composition (B₂O₃)_0.10–(P₂O₅)_0.40–(CuO)_0.50?x–(MoO₃)_x; 0.05 ? x ? 0.50 have been investigated for room temperature density and dc conductivity over the temperature range from 350 to 650 K. The density decreased with increase in MoO₃ over the composition range studied except a slight increase around 0.35 mole fraction. The observed initial decrease in conductivity with the addition of MoO₃ has been attributed to the hindrance offered by the Mo⁺ ions to the electronic motions. The observed peak-like behavior in conductivity in the composition range 0.20 – 0.50 mol% of MoO₃ is ascribed to the mixed transition metal ion effect (MTE). Mott’s small polaron hopping model has been used to analyze the high temperature conductivity data and the activation energy for conduction has been determined. The low temperature conductivity has been analyzed in view of Mott’s and Greaves variable range hopping models. It is for the first time that conduction mechanisms have been explored and MTE detected in mixed transition metal ions doped borophosphate glasses.     

Preparation and properties of porous glass using fly ash as a raw material

The porous glasses were prepared by a conventional phase separation method using coal fly ash as a raw material, and the properties of these porous glasses were investigated. The composition of coal fly ash is basically composed of SiO₂–Al₂O₃–Fe₂O₃–CaO system and the SiO₂–B₂O₃–Al₂O₃–CaO–Na₂O system of glass was chosen as base glass composition. The pore diameter increases proportional to cube root of heating time (t^1/3), however, the early stage of phase separation is not clear. It is estimated that the rate determining step may be the diffusion process of structural units involving oxygen ions and the phase separation may take place by the nucleation and growth mechanism, and the relatively larger pores of above 1 μm can be obtained easily. The chemical composition of porous glasses is SiO₂–B₂O₃–Al₂O₃(–CaO–Na₂O). A relatively large amount of fly ash (>40%) can be used successfully for the preparation of porous glass.