Ionic transport studies of the glassy silver vanadomolybdate system

Ionic conductivity of the Ag₂O-MoO₃-V₂0₅ system has been studied over a wide range of frequency, temperature and composition. A narrower glass forming region has been found in comparison to the corresponding Ag₂O-MoO₃-P₂O₅ and Ag₂O-B₂O₃-P₂O₅ systems. The highest conductivity at room temperature, _rt, = 3.21 × 10^–6–1 cm^–1 (d.c.) with an activation energy,E _act, of 0.466 eV, was observed for the glass former's ratio of unity. Further, it reached a maximum value of 2.2 × 10^–2¨-1 cm^–1 withE _act = 0.153 eV when the oxide-base glass was dissolved with Agl. D.c. conductivity, hopping rate and relaxation time in the present system have been found to be characterized by the same activation energy.     

A.c. conductivity for amorphous TeO2-P2O5 glass system

The a.c. conductivity for the TeO₂-P₂O₅ glassy system was measured in the temperature range 300–573 K and in the frequency range 100 Hz to 10 kHz. The a.c. conductivity () increased with frequency according to the relation ()^s. The frequency exponent s was found to decrease with increasing temperature. The composition dependence of the conductivity was also investigated. The density of states was also calculated using the Elliott model. The a.c. conductivity increased over the studied temperature range. The obtained experimental data have been analysed with reference to various theoretical models. The analysis shows that the correlated barrier hopping (CBH) model is the most appropriate mechanism for conduction in the TeO₂-P₂O₅ glass system.     

AC conductivity of Se-Ge-As glassy system in relation to rigidity percolation

Measurements of conductivity (ac & dc) and dielectric constant () have been made for amorphous alloyed samples of Se_0.75Ge_0.25–x As _x with x= 0.05, 0.10, 0.15 and 0.20 at different temperature (289 to 389 K) and various frequencies (10²to 10⁵Hz). The conductivity and the dielectric constant of these glasses have been explained on the basis of the correlated barrier hopping (CBH) model. Recent progress in applying percolation theory to explain properties and glass forming ability of chalcogenide glasses is critically reviewed. Percolation theory is shown to be relevant to the liquid-state behavior of glass-forming ability of the Se_0.75Ge_0.25–x As _x chalcogenide system. The relationship between the optical gap (E _g) and chemical composition is also discussed in terms of the average heat of atomization (H _s) and the average coordination number (r). These findings provide to some extent an important link between experimental and theoretical results.     

A simple technique for a.c. conductivity measurements

An inexpensive, indigenous and a simple electronic instrument based on voltage follower, currentto-voltage converter, zero crossing detector and a phase detector has been developed for measurement of a.c. conductivity. Real and imaginary parts of complex impedance are determined for a given sample as a function of frequency and the given sample is represented by a pure electronic model.     

Structural and electrical conductivity studies on nanocrystalline undoped and silver doped zinc sulphide

Zinc sulphide (ZnS) and silver doped zinc sulphide nanocrystallites (ZnS:Ag) of average size 4 and 8 nm, respectively, have been synthesized by chemical precipitation technique. The structural and morphological studies using X-ray and high resolution transmission electron microscopy (HRTEM) measurements have confirmed hexagonal structure for the samples. Using the impedance spectroscopy method, the effect of grain interior and electrode–sample interface effect on their conductivity have been studied at various temperatures. In high temperature region, the electrode–sample interface effect is found to be larger than that of the grain interior region. Further, the results of the activation energies of the charge carriers in both the regions are determined and analyzed. The conduction mechanism of silver doped zinc sulphide nanocrystallites has been studied at various temperatures and the results are reported.     

Optical parameter studies of thermally evaporated As-Se-Sn glassy system

The optical properties of As₃₀Se_70-xSn_x with (x = 0, 1, 2 and 3 at Sn %) thin films have been investigated. The films used in these studies were thermally evaporated. The structural characterization revealed that the as-deposited films were amorphous in nature. The spectral and optical parameters have been investigated using spectrophotometric measurements of transmittance in the wavelength range (200–1100 nm). The optical constants were determined from the interference maxima and minima using the Swanepole method. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-Didomenico model. The optical-absorption edge and the optical band gap are calculated from the absorption coefficient values using the non direct transition model proposed by Tauc’s extrapolation procedure. The relation between the optical gap and chemical composition in As-Se-Sn glassy system is discussed in terms of the average heat of atomization H_s and the average coordination number N_c.     

Structure and ionic transport studies of sodium borophosphate glassy system

Sodium borophosphate glasses of composition (mol%) 50Na₂O–50[xB₂O₃–(1−x)P₂O₅], 0 ≤ x ≤ 0.8 have been prepared by melt quenching method and characterized through XRD, DSC, FTIR and impedance spectroscopy techniques. The glass transition temperature increases with the substitution of B₂O₃ due to the cross-linking of the network and the FTIR study shows the presence of different structural units in the network. The ionic conductivity study as a function of composition of B₂O₃ shows increment in conductivity with two conductivity maxima at 10 and 30 mol% of B₂O₃ and conductivity variations with temperature follow an Arrhenius type behaviour. Transport numbers evaluated for ions and electrons show that Na⁺ ions are the mobile species in the investigated systems. The frequency dependence of the electric conductivity follows a simple power law feature. The analysis of various electrical parameters as a function of temperature in different complex planes shows that the charge transport occurs by the hopping mechanism.     

TeO_2-Nb_2O_5-BaO-BaCl_2系统玻璃结构及银纳米晶引入研究

碲酸盐氧卤玻璃具有低声子能以及较好的稳定性和析晶性能等优秀的综合品质,是一类很有前途的光学玻璃材料。采用熔融法制备了不同组成的TeO2-Nb2O5-BaO-BaCl2系统玻璃,研究了网络结构变化和组成对该系统玻璃的成玻璃性能和析晶性能的影响,同时探讨了向玻璃基体内引入银纳米晶体的可能性。结果表明,BaCl2的引入使得玻璃网络结构中键合及基团种类增多,碲氧链间的连接加强,网络结构更加紧密,并且成玻璃区域有所扩展。TeO2-Nb2O5-BaO-BaCl2系统玻璃基体在保持自身结构稳定性的同时,更有利于AgCl纳米晶体析出,是一种适合金属纳米晶掺杂的优良光学玻璃基体材料。     

Vibrational coherence of self-organized silver nanocrystals in f.c.c. supra-crystals

Fabrication of devices from inorganic nanocrystals normally requires that they are self-organized into ordered structures. It has now been demonstrated that nanocrystals are able to self-organize in a 'supra'-crystal with a face-centred cubic (f.c.c.) structure. The physical properties of nanocrystals self-organized into compact arrays are quite different from those of both isolated nanocrystals and the bulk phase. The collective optical and magnetic properties of these nanocrystal assemblies are governed mainly by dipolar interactions. Here, we show that nanocrystals vibrate coherently when they are self-organized in f.c.c. supra-crystals. Hence, a phase relation exists between the vibrations of all of the nanocrystals in a supra-crystal. This vibrational coherence can be observed by a substantial change of the quadrupolar low-frequency Raman scattering peak. Although a change in electronic transport properties has previously been observed on self-organization of silver nanocrystals, vibrational coherence represents the first intrinsic property of f.c.c. supra-crystals.     

D.c. conductivity of amorphous CulnSe2 films

Journal of Materials Science Letters -     

Synthesis and electrical conductivity of crystalline and glassy alloys in the Ag3GeS3Br-GeS2 system

We have studied the formation of crystalline and glassy alloys in the Ag₃GeS₃Br-GeS₂ system (0–52 mol % GeS₂; Ag₃GeS₃Br is a glass-forming phase of variable composition) and determined the crystallographic parameters of the Ag_3.179(9)Ge_1.474(5)S₄Br alloy as the saturated solid solution of GeS₂ in Ag₃GeS₃Br: sp. gr. P2₁3, a = 10.16572(3) Å, Z = 4. The electrical conductivity of the crystalline and glassy alloys was measured in the temperature range 250–410 K by a dc probe technique. The current carriers in the alloys are silver cations and halogen anions. We obtained materials with superionic conductivity and proposed a model for conduction in the alloys.     

A.c. conductivity and dielectric study of LiNiPO4 synthesized by solid-state method

LiNiPO₄ compound was prepared by the conventional solid-state reaction. The sample was characterized by X-ray powder diffraction, infrared, Raman analysis spectroscopy and electrical impedance spectroscopy. The compound crystallizes in the orthorhombic system, space group Pnma with a = 10·0252(7) Å, b = 5·8569(5) Å and c = 4·6758(4) Å. Vibrational analysis was used to identify the presence of \( \mathrm{PO}_4^{3- } \) – group in this compound. The complex impedance has been measured in the temperature and frequency ranges 654–716 K and 242 Hz–5 MHz, respectively. The Z′ and Z″ vs frequency plots are well-fitted to an equivalent circuit consisting of series of combination of grains and grain boundary elements. Dielectric data were analysed using complex electrical modulus M* for the sample at various temperatures. The modulus plots are characterized by the presence of two peaks thermally activated. The frequency dependence of the conductivity is interpreted in terms of equation: \( {\sigma_{\mathrm{a}.\mathrm{c}.}}\left( \omega \right)=\left[ {{{{{\sigma_{\mathrm{g}}}}} \left/ {{\left( {1+{\tau^2}{\omega^2}} \right)}} \right.}+\left( {{{{{\sigma_{\infty }}{\tau^2}{\omega^2}}} \left/ {{1+{\tau^2}{\omega^2}}} \right.}} \right)+A{\omega^{\mathrm{n}}}} \right] \) . The near values of activation energies obtained from the analysis of M″, conductivity data and equivalent circuit confirms that the transport is through ion hopping mechanism dominated by the motion of Li⁺ in the structure of the investigated material.     

Mixed mobile ion effect on a.c. conductivity of boroarsenate glasses

In this article we report the study of mixed mobile ion effect (MMIE) in boroarsenate glasses. DSC and a.c. electrical conductivity studies have been carried out for $\boldsymbol{x}$ MgO?C(25 $\boldsymbol{-}$ $\boldsymbol{x}$ )Li ₂ O?C50B ₂ O ₃ ?C25As ₂ O ₃ glasses. It is observed that strength of MMIE in a.c. conductivity is less pronounced with increase in temperature and frequency. The results were explained on the basis of structural model (SM) proposed by Swenson and his co-workers supporting molecular dynamic results.     

Preparation and d.c. conductivity studies of amorphous layers with the composition Ge35Se53Te10Hg2

The preparation of thin amorphous layers with the integral composition Ge₃₅Se₅₃Te₁₀Hg₂ by free evaporation of the glass Ge_33.3Se_50.0Te_8.35Hg_8.35 (mol.%) in vacuo is reported. The origin of concentration gradients perpendicular to the film plane is discussed with the help of data obtained from chemical analyses of the layers and from mass spectrometric investigations. The influence of the concentration gradients on a slight asymmetry of the current-voltage characteristics controlled by the Poole-Frenkel effect of single centres is shown. The analysis of the high field conductivity also demonstrates different effective permittivities for the two field directions.