Application of Ag–Ge–Se based chalcogenide glasses on ion-selective electrodes

Chalcogenide glasses (ChG) have proven to be promissory materials for their application as sensitive membranes in ion-selective electrodes (ISE’s), which are used in electrochemical sensors in order to detect heavy metal ions in solutions. AgGeSe system is not an exception. ChG system Ag_x(Ge_0.25Se_0.75)_100−x with x between 10 and 25 at.% was investigated as membrane material in ion-selective electrodes. This system has shown sensitivity to the presence of Cu²⁺ and Fe³⁺ ions. The introduction of Cu or Fe to the ChG composition was made in order to explore the role of metal addition on selectivity towards Cu²⁺ or Fe³⁺ ions. The analytical properties such as reproducibility, linear range, sensitivity, detection limit and working pH range were studied and its dependence on the ChG composition was analyzed for the three systems. The cross-selectivity of some interfering ions was investigated.     

Micro-structural studies of GeSe2–Ga2Se3–MX (MX = CsI and PbI2) glasses using Raman spectra

Microstructure of the chalcohalide glasses: GeSe₂–Ga₂Se₃–CsI and GeSe₂–Ga₂Se₃–PbI₂ ternary system were investigated by Raman spectra, lifetime of Dy³⁺ infrared emission and glass transition temperature (T_g). The evolution of the Raman spectra shows that the fundamental structural groups of these studied glasses consist of [Ge(Ga)Se₄] tetrahedral and some complex structure units [Ge(Ga)I_xSe_4?x](x = 1–4). The x value varied when the different iodide was added in Ge–Ga–Se matrix. For GeSe₂–Ga₂Se₃–CsI glasses, the [Ge(Ga)I_xSe_4?x](x = 1–4) mixed-anion tetrahedral and [Ga₂I₇]^? units occurred. For GeSe₂–Ga₂Se₃–PbI₂ glasses, the [Ge(Ga)I₂Se₂], [Ge(Ga)I₃Se] units can be formed. The changes of Dy³⁺ infrared emission lifetime and T_g support the results. Additionally, [PbI_n] structural units will be formed in GeSe₂–Ga₂Se₃–PbI₂ glasses due to high form-ability of these units when the PbI₂ content is high.     

Glass forming region in the GeSe2–GeTe–PbTe system and some physicochemical properties of glassy alloys

New chalcogenide glasses from the GeSe₂–GeTe–PbTe system were synthesized. The glass forming region was determined using visual, X-ray diffraction and scanning electron microscopy analyses. It is extended towards the GeSe₂ and lies partially on the GeSe₂–GeTe (0–58 mol% GeTe) and GeSe₂–PbTe (20.0–57.5 mol% PbTe) sides. No glasses were obtained in the GeTe–PbTe system. The investigated physicochemical properties vary between 4.04–6.21 g/cm³ (density, d); 97–121 kgf/mm² (microhardness, HV); ?0.187 ÷ 0.007 (compactness, C) and 14.3–17.8 GPa (elasticity modulus, E), respectively.     

Structural characterization and phase transformation kinetics of Se58Ge42−xPbx (x = 9, 12) chalcogenide glasses

The glass transition behavior and crystallization kinetics of Se₅₈Ge_42?xPb_x (x = 9, 12) have been investigated using Differential Scanning Calorimetry (DSC) at five different heating rates under non-isothermal conditions. It has been observed that these glassy systems exhibit single glass transition and double crystallization on heating. The XRD pattern revealed that the considered glasses get crystallized into GeSe₂ and PbSe/Se phases after annealing at 633–643 K for 2 h. The GeSe₂ and Se phases were found to crystallize in monoclinic structure while, PbSe phase crystallizes in cubic structure. Besides this, a mixed phase was also observed in DSC thermograms after annealing. The kinetic studies include determination of various parameters such as Avrami exponent (n), frequency factor (K_o), dimensionality of growth (m), the activation energy for glass transition (E_t) and for crystallization (E_c). The values of E_t increases while that of E_c decreases after annealing. Also, dimensionality of growth decreases to one dimension from two and three dimensions after annealing.     

Ab initio calculation of vibrational frequencies of GexSe1−x glass

We have used the density functional theory to make the models of Ge_xSe_1?x glass for which the energy is a minimum. The clusters, Ge₂Se₂, Ge₂Se₃, Ge₃Se, Ge₃Se₂, Ge₄Se, GeSe₃, GeSe₄, chain mode zig-zag Ge₄Se₃, corner sharing GeSe₄, and edge sharing Ge₂Se₆, have been made successfully and their vibrational spectra have been calculated from the first principles. We are able to optimize the bond distances as well as the bond angles. The calculated values of the frequencies of vibrations of the various clusters have been compared with those obtained from the experimental Raman spectra of actual glasses, Ge_xSe_1?x(0 < x < 0.3). The local concentration, x within 0.25 nm is nonuniform in the amorphous material. When the same cluster occurs in two stable configurations, low frequency vibrations of frequency, ν < 100 cm^?1, are found. The corner sharing GeSe₄ has low frequency modes at 54 cm^?1 and 93 cm^?1 whereas these modes disappear in the pyramidal configuration. The low frequency modes are therefore associated with the breaking of C₄ symmetry of the pyramidal configuration. The computed vibrational frequencies of clusters Ge₃, Ge₄Se₃, Ge₂Se₃, GeSe₃ and Ge₃Se₂ are actually present in the Raman spectra of the glass, Ge_xSe_1?x(0 < x < 0.3).     

Viscosity of (GeSe2)x(Sb2Se3)1−x undercooled melts

Viscosity of (GeSe₂)_x(Sb₂Se₃)_1−x undercooled melts (x = 0.4-0.8) was measured using parallel-plate method and penetration method. By using these two techniques viscosity of the whole measurable region of undercooled melt and of the part of glass region can be measured. In this relatively broad viscosity interval (seven orders of magnitude) all measured samples show Newtonian behavior and the dependence of their viscosity on temperature can be described by a simple Arrhenius equation. The kinetic fragilities calculated from these dependencies show similar compositional dependence as heat capacity changes at glass transition measured by DSC.     

Differential thermal analysis of Ag–Ge–Se,Ge–Se charge materials in the process of their heating and Ag8GeSe6, GeSe2 compound synthesis

This is the first comprehensive study of the processes of phase transformations (PT) and chemical reactions (CR) that accompany Ge–Se and Ag–Ge–Se charge material heating in stoichiometric proportions corresponding to GeSe₂ compounds, Ag₈GeSe₆ argyrodite and elementary selenium. The investigation was carried out by means of the differential thermal analysis (DTA) method. The PT in selenium and the main types of PT and CR of the formation of GeSe₂, Ag₈GeSe₆ compounds have been identified. The characteristic heats and temperature ranges of reaction processes have been determined. Ag₈GeSe₆ and GeSe₂ compounds formation has been experimentally demonstrated due to the DTA and X-ray analysis.     

Structure modeling for covalently bonded network glasses

The structure of covalently bonded network glasses is investigated in detail, through the example of GeSe₂, using a combination of experimental and computational tools. Experimentally, neutron and high-energy X-ray diffraction measurements have been carried out on amorphous GeSe₂ at KENS-KEK and SPring-8, respectively, and are used in conjunction with data from a previous neutron diffraction with isotopic substitution (NDIS) study [Petri et al., Phys. Rev. Lett. 84 (2000) 2413]. Reverse Monte Carlo modeling, employing the GeSe₂ crystal structure as a computational starting point, reproduces well the partial structure factors obtained from NDIS. RMC simulations also model well the total structure factors of the current neutron and X-ray diffraction experimental data. The analysis of all results reinforce evidence for intermediate range ordering in GeSe₂ glasses, and suggest that atomic arrangements of Ge atoms are considered to have a very important role for this intermediate range ordering.     

Optical properties and structure of thin films from the system GeSe2-Sb2Se3-AgI

Chalcohalide glasses from the GeSe₂-Sb₂Se₃-AgI system were synthesized by taking preliminary prepared GeSe₂, Sb₂Se₃ and AgI in their molecular percentages and melting them in an evacuated quartz ampoule. Thin films from the above system were deposited using vacuum thermal evaporation at different conditions on optical glass substrates BK-7. Using X-ray microanalysis it was found that the film composition differs in a certain degree from the bulk composition. Optical transmission and reflection measurements were carried out in the spectral range 400-2500 nm. The optical constants of films thicker than 400 nm (refractive index, n, and absorption coefficient, k) and the film thickness (d) were calculated using a method developed by Konstantinov. The values of n change from 2.38 for thin GeSe₂ films up to 3.48 for thin Sb₂Se₃ films while the optical band gap decreased from 1.92 eV to 1.29 eV, respectively. After exposure to light the photo-induced changes in the optical parameters were negligible for GeSe₂ and Sb₂Se₃ films and increase for some of the ternary samples. Using IR spectroscopy some conclusions about changes in the film structure were drawn.     

Surface Chemical Bonding States and Ferroelectricity of Pb(Zr0.52Ti0.48)O3 Thin Films

The surface chemical bonding states and the ferroelectric properties of sol‐gel deposited lead zirconate titanate [Pb(Zr_0.52Ti_0.48)O₃, PZT] thin films coated on (111)Pt/Ti/SiO₂/Si substrates were investigated. X‐ray photoelectron spectroscopy (XPS) was used to determine the oxidation state of the surface and the chemical composition as a function of depth in ferroelectric PZT thin layers. Values for the dielectric constant and dissipation factor at 1 kHz for the 300 nm‐thick film were 1214 and 0.014 for the film annealed at 520 °C, and 881 and 0.015 for a film annealed at 670 °C. Measured values for the remanent polarization (P_r) and coercive field (E_c), from polarization‐electric field (P‐E) hysteresis loops biased at 10 V at a frequency of 100 Hz, were 16.7, 14.4 μC/cm² and 60, 41.7 kV/cm for 520 °C and 670 °C. The leakage current density (J) was 72 and 96 nA/cm² at an applied field of 100 kV/cm. It was found that the bonding states of lead and oxygen in the surface regions could be correlated with the ferroelectric properties of the integrated thin layers.     

Low frequency Raman scattering in chalcogenide glasses

Low frequency Raman spectra of chalcogenide glasses are analyzed in terms of matrix element effects and modes of a layered structure. The spectra of GeSe₂ at low temperature shows no peaks which can be assigned to layer modes. The reduced spectra indicates that the density of states exhibits nearly ω² dependence for ω < 60 cm^?1, and the coupling constant approaches ω² dependence at frequencies less than 20 cm^?1.     

X‐ray powder diffraction study of the semiconducting alloy Cu2Cd0.5Mn0.5GeSe4

The structure of the semiconducting alloy Cu₂Cd_0.5Mn_0.5GeSe₄ was refined from an X‐ray powder diffraction pattern using the Rietveld method. The present alloy crystallizes in the wurtz‐stannite structure, space group Pmn2₁ (N^o 31), and unit cell parameters values of a = 8.0253(2) Å, b = 6.8591(2) Å, c = 6.5734(2) Å and V = 361.84(2) ų. The structure exhibits a three‐dimensional arrangement of slightly distorted CuSe₄, Cd(Mn)Se₄ and GeSe₄ tetrahedras connected by corners. © 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Synthesis and characterization of a lead(II) complex [Pb(phen)(H<Subscript>2</Subscript>O)(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>] (phen = 1,10-phenanthroline)

The monomeric lead(II) complex, [Pb(phen)(H₂O)(NO₃)₂] was prepared by a hydrothermal reaction of Pb(NO₃)₂, nitrilotriacetic acid, NaOH, 1,10-phenanthroline, and H₂O. The structure was determined by X-ray crystallography. It crystallizes in monoclinic P2(1)/n space group with the crystal cell parameters of a = 6.3568(6), b = 20.2345(19), c = 11.2722(9) Å, β = 98.337(4)^°, V = 1434.6(2) ų, and Z = 4. The crystal X-ray analysis shows that the lead atom is six-coordinated by two N atoms of phen ligand, three oxygen atoms of nitrate anions and one water molecule. Owing to the presence of a lone pair of electrons of lead atom, a significant gap occurs in the coordination geometry around Pb ion. A 3D architecture is formed through the strong hydrogen bonding and π–π stacking interactions.     

Electrical properties of TiO2 thin films

The electrical properties of n-type titanium dioxide thin films deposited by magnetron-sputtering method have been investigated by temperature-dependent conductivity. We observed that the temperature dependence of the electrical conductivity of titanium dioxide films exhibits a crossover from T^?1/4 to T^?1/2 dependence in the temperature range between 80 and 110 K. Characteristic parameters describing conductivity, such as the characteristic temperature (T₀), hopping distance (R_hop), average hopping energy (Δ_hop), Coulomb gap (Δ_C), localization length (ξ) and density of states (N(E_F)), were determined, and their values were discussed within the models describing conductivity in TiO₂ thin films.     

Ion transport behavior in a new fast Ag ion conducting composite electrolyte system: 0.85[0.75AgI:0.25AgCl]:0.15CeO2

Investigations on ion transport behavior of a new fast Ag⁺ ion conducting composite electrolyte system: 0.85[0.75AgI:0.25AgCl]: 0.1CeO₂ are reported. An alternate host: ‘[0.75AgI:0.25AgCl] mixed system/solid solution’ has been used as first-phase host matrix salt, in place of the traditional host AgI, while the micron-size particles of an insulating and chemically inert CeO₂ as second-phase dispersoid. The soaking time, plays important role in determining the conductivity enhancement in the composite system. The system: 0.85[0.75AgI:0.25AgCl]:0.1CeO₂ prepared at soaking time ∼10 min. exhibited optimum conductivity:σ_rt ∼ 1.2 × 10⁻³ S cm⁻¹ at room temperature, which is an order of magnitude higher than that of the pure host. Structural characterization studies were performed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Temperature dependent measurement on the basic ionic parameters viz. conductivity (σ), ionic mobility (μ), mobile ion concentration (n), room temperature ionic transference number (t_ion) and ionic drift velocity (v_d) have been carried out on the system.     

Bulk and impurity infrared absorption in 0.5 As2Se30.5 GeSe2 glass

A study of infrared absorption in the 250–4000 cm^?1 region has been carried out for 0.5 As₂Se₃0.5 GeSe₂ glasses quantitatively doped with oxide impurity. The frequencies of the intrinsic 2- and 3-phonon absorption bands at 490 and 690 cm^?1 correspond well to those predicted from combinations of the high frequency bands in the first order IR and Raman spectra of As₂Se₃ and GeSe₂ glasses.Glasses doped with As₂O₃ exhibit the same oxide impurity absorptionbands as those doped with GeO₂. Unlike As₂Se₃ glass, at impurity concentrations up to 1000 ppm As₂O₃, 0.5 As₂Se₃0.5 GeSe₂ glass exhibits only one major oxide impurity species, characterized by absorption bands at 780 and 1260 cm^?1 and due to oxygen bonded to network Ge. The observation of a much weaker network AsO vibration band at 670 cm^?1 confirms that oxygen bonds preferentially to Ge in this glass. The same minor oxide species appears to determine excess IR absorption at the CO₂ laser wavelength of 10.6 μm in both As₂Se₃ and 0.5 As₂Se₃ 0.5 GeSe₂ glasses. The frequencies and intensities of absorption bands due to hydrogen impurities are also quite comparable for these two materials.     

A low silica, barium borate glass-ceramic for use as seals in planar SOFCs

A low silica, barium borate glass-ceramic for use as seals in planar SOFCs containing 64 mol%BaO, 3 mol%Al₂O₃ and 3 mol%SiO₂ was studied. Coefficient of thermal expansion (CTE) between 275-550 °C, glass transition temperature (T_g), and dilatometric softening point (T_s) of the parent glass were 11.9 × 10⁻⁶ °C⁻¹, 552 °C, and 558 °C, respectively. Glass-ceramic was produced by devitrification heat treatment at 800 °C for 100 h. It was found that nucleation heat treatment, seeding by 3 wt%ZrO₂ as glass-composite and pulverization affected the amount, size and distribution of crystalline phases. SEM-EDS and XRD results revealed that crystalline phases presented in the devitrified glass-ceramic were barium aluminate (BaAl₂O₄), barium aluminosilicate (BaAl₂Si₂O₈) possibly with boron associated in its crystal structure, and barium zirconate (BaZrO₃). CTE of the devitrified glass-ceramic was in the range of (10.1-13.0) × 10⁻⁶ °C⁻¹. Good adhesion was obtained both in the cases of glass and devitrified glass-ceramic with YSZ and AISI430 stainless steel. Interfacial phenomena between these components were discussed.     

Structure of liquids and glasses in the Ge–Se binary system

A summary is given of the partial structure factors that have been measured for liquids and glasses in the Ge–Se binary system by using diffraction methods. Information is presented on the pair correlation functions describing the atomic species and use is made of the Bhatia–Thornton formalism to separate those pair correlation functions describing the system topology from those that describe the chemical ordering. The information made available by the measured Bhatia–Thornton partial structure factors on the thermodynamic properties of Ge–Se mixtures is briefly summarized. The properties of the network structures formed in liquid and glassy Ge–Se compounds are investigated as a function of composition, temperature and pressure. For GeSe₂ at ambient pressure it is shown that the so-called first sharp diffraction peak, which appears in the measured diffraction patterns at a small scattering wavevector value of ≈1 Å⁻¹ and which is associated primarily with Ge–Ge correlations, does account for discernable features of the observed intermediate range order in both the liquid and glassy phase. The first sharp diffraction peak in the measured Ge–Ge partial structure factor for both phases is described by comparable parameters suggesting communality in the underlying intermediate range order which survives the glass transition. Homopolar bonds are found to be a feature in the structure of liquid GeSe and both liquid and glassy GeSe₂ with Ge–Ge and Se–Se distances in the ranges 2.33(3)–2.42(2) and 2.30(2)–2.34(2) Å, respectively.