Results of differential scanning calorimetric (DSC) under non-isothermal conditions on three compositions of GexSe92-xIn8 (x = 10, 12.5 and 15 at%)) are reported and discussed. It is seen that these glasses exhibit a double glass transition and single-stage crystallization on heating. The glass transition temperature (Tg), the onset crystallization temperature (Tc) and the peak temperature of the crystallization (Tp) were found to be dependent on the composition and the heating rates. The activation energy for glass transition (Eg) and for crystallization (Ec) are evaluated and their composition dependence is discussed. The crystallization phases resulting from the DSC have been identified using X-ray diffraction and scanning electron microscopy (SEM). The results indicated that the crystallization mechanism occurs in one, two and three dimensional growth according to Avrami exponents (n). The kinetic parameters determined have made it possible to discuss the glass-forming ability

X-ray scattering has been used to investigate the structure of glassy As2Te3, prepared by quenching in liquid nitrogen. The result of the coherent scattered x-ray intensity proved that the medium-range order (MRO) is very weak, and this was attributed to the higher metallic nature of the glass. Analysis of the first two peaks in the curve of the total radial distribution function, T(r), revealed that the short-range order (SRO) in the glassy state is different from that in the crystalline state, and that the first coordination sphere includes As–As and Te–Te bonds in addition to the As–Te bonds

In this study, amorphous chalcogenide Cu10Se90 and Cu20Se80 thin films have been obtained by thermal evaporation deposition process on well-cleaned quartz substrates. Thin films were annealed at various temperatures in N2 atmosphere. X-ray diffraction patterns (XRD) showed that the films are like amorphous in nature for as prepared but annealed films produced crystalline peaks and that their crystallinity was proportional to annealing temperature. Thin film morphologies were examined using scanning electron microscopy (SEM). The optical absorption coefficient (α) for the as-deposited and annealed films was calculated using spectrophotometer measurements of the transmittance (T) and reflectance (R) at normal incidence of light in the wavelength range 200–2500 nm. The optical band gap (Eg) was found to be around 2.281 and 2.231 eV for as-prepared Cu10Se90 and Cu20Se80 thin films respectively, (Eg) showed a decrease with increasing of the annealing temperature higher than the glass transition temperature (Tg). The high frequency dielectric constant (ε∞) and the ratios of the carrier concentration to the effective mass (N/m*) were also determined for the as-deposited and annealed films. The dispersion of the refractive index is discussed in terms of the single-oscillator model. The oscillator energy Eo and the dispersion energy Ed were obtained. The results are discussed and correlated in terms of amorphous–crystalline transformations

In this study, amorphous chalcogenide Cu10Se90 and Cu20Se80 thin films have been obtained by thermal evaporation deposition process on well-cleaned quartz substrates. Thin films were annealed at various temperatures in N2 atmosphere. X-ray diffraction patterns (XRD) showed that the films are like amorphous in nature for as prepared but annealed films produced crystalline peaks and that their crystallinity was proportional to annealing temperature. Thin film morphologies were examined using scanning electron microscopy (SEM). The optical absorption coefficient (α) for the as-deposited and annealed films was calculated using spectrophotometer measurements of the transmittance (T) and reflectance (R) at normal incidence of light in the wavelength range 200–2500 nm. The optical band gap (Eg) was found to be around 2.281 and 2.231 eV for as-prepared Cu10Se90 and Cu20Se80 thin films respectively, (Eg) showed a decrease with increasing of the annealing temperature higher than the glass transition temperature (Tg). The high frequency dielectric constant (ε∞) and the ratios of the carrier concentration to the effective mass (N/m*) were also determined for the as-deposited and annealed films. The dispersion of the refractive index is discussed in terms of the single-oscillator model. The oscillator energy Eo and the dispersion energy Ed were obtained. The results are discussed and correlated in terms of amorphous–crystalline transformations

The optical properties of as-deposited GexSe92-xIn8 (x = 10, 12.5, 15 and 20 at%) have been studied. Various optical constants have been calculated for the studied compositions. The mechanism of the optical absorption follows the rule of non-direct transition. It was found that, the optical energy gap (Eg) decreased with increasing Ge content. This result can be interpreted on the basis of the chemical-bond approach proposed by Bicermo and Ovshinsky. The values of the refractive index (n) and the extinction coefficient (k) increased with increasing Ge content. Annealing of Ge12.5Se79.5In8 films at temperature higher than the glass transition temperature was found to decrease the optical energy gap. Electrical conductivity was measured in the temperature range (300-450 K) for the studied compositions. The effect of composition on the activation energy (ΔE) and the density of localized states at the Fermi level N(EF) were studied. The electrical conductivity measurements show two types of conduction channels that contribute two conduction mechanisms. On the other hand, the electrical resistivity and the activation energy were found to decrease with increasing the annealing temperature. Transmission electron microscope (TEM) investigation indicates the separation of crystalline phase after annealing at the temperatures higher than the glass transition. The results were discussed on the basis of amorphous crystalline transformations

Amorphous Ag10Te90 thin films were prepared onto glass substrates using the thermal evaporation method. The effect of γ-irradiation on the optical parameters was investigated in the dose range 10–180 krad. The optical absorption coefficient (α) for the as-deposited and irradiated films has been determined from the reflectance (R) and transmittance (T) measurements in the wavelength range 400–900 nm. Analysis of the spectral behavior of the absorption coefficient in the absorption region revealed direct transitions. The optical studies showed the decrease in band gap (Eopt) with an increase in γ-irradiation . The width of the tails of localized states (Ee) were calculated and found to be increasing after γ-irradiation. Dielectric related optical constants, such as (n, kex., ε1 and ε2), were presented. Finally, the effect of γ-irradiation on the high-frequency dielectric constant (εL) and carrier concentration (N/m*) is also studied. The results were discussed by the change on the degree of disorder as well as the radiation-induced effect on solids.

Amorphous Ag10Te90 thin films were prepared onto glass substrates using the thermal evaporation method. The effect of γ-irradiation on the optical parameters was investigated in the dose range 10–180 krad. The optical absorption coefficient (α) for the as-deposited and irradiated films has been determined from the reflectance (R) and transmittance (T) measurements in the wavelength range 400–900 nm. Analysis of the spectral behavior of the absorption coefficient in the absorption region revealed direct transitions. The optical studies showed the decrease in band gap (Eopt) with an increase in γ-irradiation . The width of the tails of localized states (Ee) were calculated and found to be increasing after γ-irradiation. Dielectric related optical constants, such as (n, kex., ε1 and ε2), were presented. Finally, the effect of γ-irradiation on the high-frequency dielectric constant (εL) and carrier concentration (N/m*) is also studied. The results were discussed by the change on the degree of disorder as well as the radiation-induced effect on solids.

The temperature dependence of the DC electrical conductivity σDC was measured in the temperature range from 300-500 K. It was found that there are double activation energies, Eσ, for Ge20Se80-xBix (x = 0, 2.5 and 5 at%) films, while there is single activation energy for Ge20Se72.5Bi7.5. when incorporation of Bi = 7.5 at%, the pre-exponential value σ0 decreases by about six order of magnitude, the activation energy in the extended states Eσ decreases from 0.96 to 0.09 eV. Also the effect of applied electric field was studied and observed that, activation energy in high temperature region increases with increasing electric field; this behavior can be understood assuming that the contribution to the conductivity activation process is due to conduction in the extended states and also due to hopping in the localized states. With the increasing electric field, as former process, which is having high activation energy, becomes more predominant due to the dumping of the carriers in the extended states, the effective activation energy of the system increases, in spite of the fact that the activation energy of the extended states conduction may remain constant. Finally, the electrical data suggests that the addition of bismuth produces localized states near the conduction band edge so that the electrical transport is due to hopping of electrons after being excited into localized states at the conduction band edge.

The temperature dependence of the DC electrical conductivity σDC was measured in the temperature range from 300-500 K. It was found that there are double activation energies, Eσ, for Ge20Se80-xBix (x = 0, 2.5 and 5 at%) films, while there is single activation energy for Ge20Se72.5Bi7.5. when incorporation of Bi = 7.5 at%, the pre-exponential value σ0 decreases by about six order of magnitude, the activation energy in the extended states Eσ decreases from 0.96 to 0.09 eV. Also the effect of applied electric field was studied and observed that, activation energy in high temperature region increases with increasing electric field; this behavior can be understood assuming that the contribution to the conductivity activation process is due to conduction in the extended states and also due to hopping in the localized states. With the increasing electric field, as former process, which is having high activation energy, becomes more predominant due to the dumping of the carriers in the extended states, the effective activation energy of the system increases, in spite of the fact that the activation energy of the extended states conduction may remain constant. Finally, the electrical data suggests that the addition of bismuth produces localized states near the conduction band edge so that the electrical transport is due to hopping of electrons after being excited into localized states at the conduction band edge.

The effects of composition and thermal annealing near crystallization temperature, Tc on the optical and structural properties of Ge20Se80−xBix (x=0, 2.5, 5 and 7.5 at%) was investigated. The influence of incorporation Bi content in Ge20Se80−xBix system results in a gradual decrease in the indirect optical gap from 1.89 to 1.44 eV, this behavior can be explained as increased tailing. On annealing, the optical band gap Eg decreases gradually for the crystallized films while the refractive index increases, this behavior can be attributed to transformation from amorphous to crystalline and was explained in the light of dangling bond model. The refractive index n of as-prepared and annealed films has been analyzed according to the Wwmple–DiDominico single oscillator model and the values of Eo and Ed were determined. The effect of annealing on the nature and degree of crystallization has been investigated by studying the structure using transmission electron microscope, X-ray diffraction and scanning electron microscope.