Preparation, characterization and conductivity studies of AgI-Ag2O-(TeO2 + P2O5) fast ionic conducting glasses

Silverphosphotellurate (SPT) quaternary fast ionic conducting (FIC) glasses of compositions AgI-Ag₂O-[(1 – x)P₂O₅ + xTeO₂], x = 0.0 to 1.0 in steps of 0.1, were prepared by melt quenching. All SPT compounds were characterized by X-ray diffraction and the amorphous nature of the samples was confirmed. The structure of all compositions was examined by Fourier Transform Infrared Spectroscopy. The glass transition temperature (T _g) was determined for all SPT samples, using differential scanning calorimetry. Complex impedance measurements were made on all glasses in the frequency range 40 Hz to 100 kHz. Impedance data were analyzed using Boukamp equivalent circuit software and the bulk conductivity was obtained. The highest conductivity ( = 1.59*10^–2 S/cm) was shown by the composition 60%AgI – 26.67%Ag₂O – 13.33% (0.3P₂O₅ + 0.7TeO₂).     

Fast ion conducting glasses: effect of preparation on conductivity and its correlation with surface analysis using SEM

Glasses in the system Agl-Ag₂O-As₂O₃ and Agl-Ag₂O-As₂O₅ were prepared by three different methods and characterized by studying their transport and surface properties. A.c. conductivity studies performed on the samples with compositions (mol %) 66.6 Agl-33.3(xAg₂O-yAs₂O₃) and 66.6 Agl-33.3 (xAg₂O-yAs₂O₅) fory/x=0.20 to 5.0 revealed that the glasses are very good ionic conductors. The highest ionic conductivity was observed for the compositions 66.6Agl-16.66Ag₂O-16.66As₂O₃ and 66.6Agl-6.66Ag₂O-16.66As₂O₅, when prepared by the open-air crucible melting and rapid quenching method and 66.6Agl-16.66Ag₂O-16.66As₂O₃ and 66.6Agl-22.2Ag₂O-11.11As₂O₅, when prepared by the vacuum-sealed quartz tube melting and zone-controlled quenching method. The observation of high ionic conductivity for different glass former/glass modifier ratios in the Agl-Ag₂O-As₂O₅ system and its dependence on the method of preparation was explained by correlating the observed surface properties. The contribution of electronic conductivity to the total conductivity was estimated by Wagner's d.c. polarization technique. The surface of the bulk specimens belonging to the highest conducting composition in both the systems was studied using a scanning electron microscope to observe the formation of precipitated - and -Agl in the form of colloids which are assumed to be responsible for high ionic conductivity.     

Sol–gel synthesis and characterization of Li2O–As2O5–SiO2 glassy system

The ternary 10% Li₂O + 90% (xAs₂O₅ + (1 − x) SiO₂) (x = 0.025, 0.05, 0.075 and 0.1) (LAS) glassy system with different compositions were prepared using sol–gel technique. All the prepared samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry techniques. The observed peak-free XRD patterns confirm the amorphous phase of the prepared LAS compounds. Structural coordination of LAS glassy samples was confirmed by Fourier transform infrared spectroscopy. Thermal behavior of the glassy samples was characterized by differential scanning calorimetry. Bulk conductivity of all the LAS glassy samples was calculated by analyzing the impedance data measured at different temperatures. Activation energy (E_a) is evaluated from the log σT vs. 1000/T plot and it is found to be 0.837 eV.     

Glass formation region and lithium ion conduction in the oxyfluorophosphate glasses

Oxyfluorophosphate glasses containing about 80 mol% of [LiF+Li₂O] show unusually high lithium ion conductivity at elevated temperatures. A detailed investigation has been carried out on the glasses prepared by both conventional cooling and a rapid quenching technique. Chemical analysis of the glasses reveals fluorine loss during melting and it becomes difficult to make glasses with exact predetermined compositions. Electrical conductivity of the glasses, determined from complex impedance analysis increases with Li₂O content. A glass with nominal composition 70 LiF15 Li₂O15 Al(PO₃)₃ shows the highest conductivity (~ 1.3×10^–3 ohm^–1 cm^–1 around 200° C) among all the compositions studied. An interesting feature of the impedance plot is the near perfect semicircle for bulk relaxation indicating a narrow distribution of relaxation times. This has been explained on the basis of a relatively small proportion of lithium ions which are mobile. The electrical conductivity of the glasses is found to be essentailly independent of dissolved water content. The infrared spectra of these glasses (2 to 50m region) could not produce much useful structural information.     

A study of the electrical properties of molybdenum phosphate glasses

A series of binary MoO₃-P₂O₅ and also ternary MoO₃-P₂O₅-In₂O₃ glasses were prepared and their electrical properties were investigated. The d.c. conductivity measurements show that the conduction in molybdenum phosphate glasses is by a hopping process in which the electrical charge transfers from Mo⁵⁺ to Mo⁶⁺ ion sites. The conductivity can be discussed in terms of the small polaron conduction mechanism. In contrast to vanadium phosphate glasses, the tunnelling term in the conductivity formula seems to make a significant contribution in molybdenum phosphate glasses and is associated with a hopping process in the non-adiabatic regime.     

Electrical relaxation of superionic conducting glasses AgX-AgPO3 (X=I,Br, Cl)

The complex impedance of superionic conducting glasses (AgX)_0.3-(AgPO₃)_0.7 (X = I, Br, Cl) was measured in the frequency range 5 Hz–500 kHz and temperatures between 299 K and 348 K. The frequency dependence of (the real part of complex conductivity) shows two regions: low and high frequencies. The first is attributed to the electrode-electrolyte polarization, while the second is attributed to the bulk conduction. The replacement of AgCl by AgBr or Agl at the same molar fraction is found to improve the bulk conductivity of the studied glasses. The electrical conductivity spectra exhibit one relaxation peak associated with dielectric loss which arises from the thermally activated jumps of Ag⁺ ions. The dependence of the relaxation time upon the halogen type is discussed in terms of the structural aspects, where the silver halides tend to form microdomains. The special characteristic of fast ionic conduction depending upon halide type is emphasized.     

Investigation of ionic conductivity in the system 60Agl-20Ag2O-20[xB2O3-(1−x)WO3]

Superionic conducting glasses in the system 60Agl-20Ag₂O-20[xB₂O₃-(1–x)WO₃] were prepared by heating the appropriate amounts of the materials in an open quartz crucible at 650 ° C and quenching the melt in liquid nitrogen. The electrical conductivity of these samples was measured at 1 kHz on pressed pellets with electrodes made up of silver powder and this electrolyte. The mixed former effect has been observed in the present system, where the conductivity of the compositions studied was greater than the individual ternary systems. The electronic contribution to the total conductivity was determined using Wagner's polarization technique. The electronic conductivity was around six orders of magnitude less than the total conductivity. The transport number was almost equal to unity.     

Effect of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> on the dynamics of Li<Superscript>+</Superscript> ions in Li<Subscript>2</Subscript>O·P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Lithium ion transport has been studied in bismuth lithium phosphate glasses in the frequency range 20 Hz–1 MHz and in the temperature range 423–573 K using impedance spectroscopy. The addition of Bi₂O₃ in Li₂O·P₂O₅ glass is related to the modification of the glass structure and facilitates the Li⁺ ions migration. The ac and dc conductivities, activation energy of the dc conductivity and relaxation frequency are extracted from the impedance spectra. Conductivity of the present glass system is found to be ionic in nature. The electrical response of the glasses has been studied using both conductivity and electric modulus formalisms. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of the dynamic processes for ions in these glasses. Nearly identical values of activation energy for dc conduction and for conductivity relaxation time indicate that the ions overcome same energy barrier while conducting and relaxing.     

Neutron diffraction study on the medium and short-range order of ternary chalcogenide glasses

Glasses from Ge_xAs_40–xS₆₀, Ge_xAs_40–xSe₆₀, Ge_xSb_40–xS₆₀ and Ge_xSb_40–xSe₆₀ families have been investigated by neutron diffraction. The well expressed first sharp diffraction peak of the neutron spectra at Q = 10–14 nm^–1 has been explained by a pseudo-binary model of the structure of studied chalcogenide glasses. The amplitude of this interference maximum increases with Ge-content in all investigated samples. Experimental radial distribution functions show that the basic structural units, GeS(Se)₄ tetrahedra and As(Sb)S₃ or As(Sb)Se₃ pyramids persist in glassy state for the whole range of studied compositions. Crystal-like model distribution functions have been used to describe the short-range order observed. A shortening of heteropolar bonds in S-containing glasses as well as an increase of heteropolar bonds length in Se-containing glasses has been found.     

Ga as an additive in the As2Te3 glass

Results of measurements of the mean atomic volume (V), the glass transition temperature (T _g), the activation energy for glass transition (E _t) and the d. c. electrical conductivity () are reported and discussed for ten glass compositions of the Ga–As–Te system. The glasses studied can be represented as Ga _x (As_0.4Te_0.6)_100–x glasses, with the additive Ga ranging from 0 to 12 atomic percent (at.%) in the parent As₂Te₃glass. In the Ga _x (As_0.4Te_0.6)_100–x glasses, changes in slope are observed in the V, T _g, E _t, and other electronic properties, at the composition with a Ga content of 2 at.%. The results are compared with those obtained on introduction of Ag and Cu to the As₂Te₃and the [0.5As₂Te₃–0.5As₂Se₃] glasses. Analysis of the data suggest formation of GaAs, Ga₂Te₃and excess Te structural units (s.u.) in lieu of some of the original As₂Te₃s.u., for addition of Ga up to 2 at.% to the parent As₂Te₃glass; for higher Ga contents, formation of GaAs, GaTe and excess Te s.u. are indicated.     

The superionic Agl-Ag2O-V2O5 system: Electrical conductivity studies on glass and polycrystalline forms

Superionic conducting glasses in the Agl-Ag₂O-V₂O₅ system were prepared by heating the appropriate amounts of raw materials at 723 K and quenching in liquid nitrogen. The polycrystalline materials were prepared by slowly cooling the melt to room temperature. X-ray diffraction was used for material characterization. The electrical conductivity of the pulverized samples, pressed together with an electrode mixture of silver and electrolyte (1:2 by weight) under 5000 kg cm^–2 pressure to form pellets 10 mm in diameter and 2 to 3 mm in thickness, was measured in the temperature range 300 to 365 K at 1 kHz. The ionic conductivities of the glasses were always higher than those of their polycrystalline counterparts, while their activation energies were also slightly higher. Conductivity measurements on annealed glassy samples indicated that the conductivity decreases with the time of annealing, and reaches a constant value which is nearly the same as that of the polycrystalline sample. Electronic conductivities of both types of sample were obtained by using Wagner's polarization cell technique, which showed that the electronic conductivity for both types was five orders of magnitude less than the total conductivity. Typical galvanic cells having the configuration Ag,electrolyte/electrolyte/C,electrolyte,I₂ were constructed and the silver ion transport number was calculated by the e.m.f. method.     

Electrical conductivity,TEP and dielectric studies on mol% 66.6 Agl-22.2 Ag2O-11.1 (0.8 V2O5-0.2 P2O5) electrolyte material for solid state batteries

In the superionic conducting quarternary system Agl-Ag₂O-V₂O₅-P₂O₅, the best ionic conductivity was obtained for the composition 66.6% Agl-33.3% (2Ag₂O-1 (V₂O₅-P₂O₅)), when the GF/GM ratio was varied from 0.20 to 5.0. Then fixing the GF/GM ratio at 0.50, the ratio of the glass formers V₂O₅ and P₂O₅ were varied and the highest conducting composition was obtained as 66.6% Agl-22.2 Ag₂O-11.1% (0.8 V₂O₅-0.2 P₂O₅). A preliminary investigation using this material in the form of an electrolyte in a solid state electrochemical cell is reported. The polycrystalline and amorphous compounds were prepared from the same melt, by open air crucible melting and the rapid quenching technique. The ionic conductivity for the best conducting polycrystalline (hence referred as 66VP82P) and amorphous (66VP82G) samples was obtained as 8.3 × 10^–3 and 4.2 × 10^{–2 –1} cm^–1 respectively. The electronic conductivity of the order 10^{–10 –1} cm^–1 was observed for 66VP82G and 10^{–8 –1} cm^–1 for 66VP82P samples. Thermoelectric power studies revealed that the charge carriers are the Ag⁺ ions, with an activation energy of 0.288eV for 66VP82G, which correlated well with the activation energy obtained from the conductivity measurements. The dielectric constant, dielectric loss and the loss tangent were calculated for both polycrystalline and glassy 66VP82 material. It was observed that the dielectric loss is more for the glassy material than the polycrystalline material. Solid state galvanic cells with 66.6% Agl-22.2% Ag₂O-11.1% V₂O₅, 66.6% Agl-22.2%-Ag₂O-11.1% P₂O₅ and 66.6% Agl-22.2% Ag₂O-11.1% (0.8 V₂O₅-0.2 P₂O₅) (coded as 66V, 66P and 66VP82 respectively) electrolytes were constructed. Both polycrystalline and amorphous electrolyte cells were fabricated for a comparative study and the polarization effects were observed to be negligible in amorphous cells. The variation of open circuit voltage with temperature was reported and the current discharge curves indicate that the 66VP82 material has higher current capacity with high current drain when compared to 66V and 66P cells.     

Effect of acid catalyst concentration on structure and conductivity studies of quaternary lithium-based glasses synthesized by sol–gel route

Lithium phosphoborosilicate (LPBS) glasses were synthesized through sol–gel process with various nitric acid concentrations, as a catalyst. Measuring the XRD patterns for the dried gel heat-treated at different temperatures optimized the synthesis temperature for the LPBS glasses. The effect of acid catalyst concentrations on the structural properties of the LPBS glasses was studied using XRD, FTIR, and DSC. Impedance measurement was carried out at different temperatures on the LPBS samples synthesized by sol–gel route with various nitric acid concentrations and impedance data were analyzed using the Boukamp equivalent circuit software. The bulk conductivity of the LPBS samples synthesized with each concentration of nitric acid, as a catalyst, was calculated from the analyzed impedance data. It was found that the LPBS sample synthesized with 2.5 N nitric acid concentration showed the highest conductivity, σ=2.28 (± 0.02)×10⁻⁷ S cm⁻¹ at 443 K. The activation energy (E_a) was obtained from Arrhenius plots of the dc conductivity of each LPBS glassy samples and was found to be 0.39 (± 0.02) eV for the highest conducting LPBS sample.     

Semi conducting properties amd microstructure of x%V2O5·(100−x)% (As2O3·B203) glasses

Binary semiconducting glasses of the x%V₂O₅·(100?x)%(As₂O₃· B₂O₃) system with x ranging from 50 to 70 mol% have been investigated to elucidate their electronic conduction and microstructure. The values of conductivity and activation energy obtained for these glasses are in agreement with previous results on most V₂O₅-based glasses. Arguments for a small-polaron conduction of nonadiabatic type are presented. All the samples show a glass-glass type phase separation.     

Peculiarities of the electric conductivity of As<Subscript>2</Subscript>S<Subscript>3</Subscript>〈Au〉 and As<Subscript>2</Subscript>S<Subscript>5</Subscript>〈Au〉 glasses

The temperature dependences of the dc conductivity in glasses of the (As₂S₃)_1−x Au_x and (As₂S₅)_1−x Au_x systems (0.04 at. % ≥x≥0) are reported for the first time. The curves show an anomalous behavior in the temperature interval of 360 K<T<300 K and exhibit a break for glass compositions with a low gold content. A model explaining the existence of impurity conductivity is proposed.     

Structural study of superionic conducting glasses Agl-AgPO3 by X-ray diffraction

Atomic structures of (Agl) _x (AgPO₃O₃)_1–x glasses for x=0.0, 0.1, 0.2, 0.3 and 0.5 have been investigated by X-ray diffraction. Coordination numbers and atomic distances in the near-neighbour region were determined by the least-squares variational method. The coordination numbers of P-O, P-P and O-O pairs are unchanged with x, which suggests no modification of the connectivity of the PO₄ tetrahedral chains by doping with Agl. The coordination number of I^– around Ag⁺ linearly increases from 0 to 1.9 ± 0.2 with increase in x, while the coordination number of O^2– around Ag⁺ linearly decreases from 5.1±0.2 to 2.5±0.2. This also suggests that the Agl gets into the PO₄ chains while keeping the local environment of the Agi itself.     

Structural, dielectric, impedance and optical properties of CaBi2B2O7 glasses and glass-nanocrystal composites

Optically clear glasses were fabricated by quenching the melt of CaCO₃–Bi₂O₃–B₂O₃ (in equimolecular ratio). The amorphous and glassy characteristics of the as-quenched samples were confirmed via the X-ray powder diffraction (XRD) and differential scanning calorimetric (DSC) studies. These glasses were found to have high thermal stability parameter (S). The optical transmission studies carried out in the 200–2500 nm wavelength range confirmed both the as-quenched and heat-treated samples to be transparent between 400 nm and 2500 nm. The glass-plates that were heat-treated just above the glass transition temperature (723 K) for 6 h retained ≈60% transparency despite having nano-crystallites (≈50–100 nm) of CaBi₂B₂O₇ (CBBO) as confirmed by both the XRD and transmission electron microscopy (TEM) studies. The dielectric properties and impedance characteristics of the as-quenched and heat-treated (723 K/6 h) samples were studied as a function of frequency at different temperatures. Cole–Cole equation was employed to rationalize the impedance data.     

Effect of nanocrystallization on the structural and electrical conductivity enhancement of vanadium-based glasses

A new glass–ceramic nanocomposites material was prepared by a thermal nanocrystallization of V₂O₅–Bi₂O₃–P₂O₅ system with different V₂O₅ content. The amorphous state of glassy materials is confirmed by X-ray diffraction. It was shown by XRD and SEM studies that by suitable heat-treatment glasses can be turned into glass–ceramic nanocomposites consisting of crystallites smaller than 80 nm inserted in the glassy matrix. Also, it was shown that thermal nanocrystallization of as-prepared glassy samples leads to creation of nanocrystalline grains of V₂O₅, Bi₂O₃, and BiVO₄ phases. The glass–ceramic nanocomposites obtained show giant enhancement of electrical conductivity than the as-prepared glasses. The conductivity enhancement was recognized to interfacial regions adjacent crystalline grains. The conduction of the present glasses and their glass–ceramic nanocomposites was confirmed to be due to primarily non-adiabatic hopping of small polaron between vanadium ions.     

Dielectric properties and polarizability of molybdenum tellurite glasses

The dielectric behaviour of the [TeO₂]_1–x [MoO₃] _x , x=0.2, 0.3 and 0.45 mol%, glassy system is reported for the temperature range 300–573 K and the frequency range of 0.1–10 kHz. Both the static and high frequency dielectric constants for these binary tellurite glasses decrease with increasing MoO₃ content. The temperature dependence of the dielectric constants of these glasses are positive. The frequency dependence of the dielectric constant identifies a frequency dependence which does not show a flattening at low frequency. The room temperature static dielectric polarizability is discussed in terms of the MoO₃ concentration. The temperature dependence of the dielectric constant has been analysed in terms of the temperature changes of both volume and polarizability and also a volume change of the polarizability.     

Experimental studies and space charge mechanism for the conductivity/mobility enhancement due to SnO2 dispersion in Ag+ ion conducting borate glass

The enhancement in ionic conductivity of a Ag⁺ ion conducting borate glass of molar % composition 55.5 Agl-22.25 Ag₂0-22.25 B₂O₃ is reported with the dispersion of SnO₂. X-ray diffraction (XRD), i.r. and optical microscopy reveals that the SnO₂ addition yields a dispersed phase material and not a new glass. The material is essentially a Ag⁺ ion conducting (Agl+Ag₂O+B₂O₃) glass in which Sn_O2 is dispersed. The direct measurement of mobility of the mobile ions reveals that the enhancement in conductivity is controlled by the enhancement in mobility. A space charge model based on the mechanism of adsorption-desorption of mobile ions near/at the interface in the space charge region creating a certain type of mobile ion concentration gradient is introduced to explain the results.