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1.
Differential scanning calorimetry (DSC) under non-isothermal conditions is used to study the crystallization kinetics of Sb14As29Se52Te5 chalcogenide glass. In addition, two approaches are used to analyze the dependence of glass transition temperature (Tg) on the heating rate (α). One is empirical linear relationship between (Tg) and ln(α). The second approach is the use of straight line vs. 1/Tg for the evaluation of the activation energy for glass transition. The phases at which the alloy crystallizes after the thermal treatment have been identified by using X-ray diffraction. The diffractogram of the transformed material shows the presence of some crystallites of As, Te, AsSb, As2Se3, Sb2Se3 and AsSe.5Te.5 in the residual amorphous matrix. 相似文献
2.
Chalcogenide glasses from the Ag2Te-As2Se3-CdTe system were synthesized. The basic physicochemical parameters such as density (d), microhardness (HV) and the temperatures of phase transformations (the glass transition Tg, crystallization Tcr and melting Tm) were measured. Compactness and some thermomechanical characteristics such as volume (Vh) and formation energy (Eh) of micro-voids in the glassy network, as well as the module of elasticity E were calculated. The overall mean bond energy 〈E〉, the mean coordination number Z, the mean bond energy of the average cross-linking/atom and the average bond energy per atom of the “remaining matrix”— and , as well as the average heteropolar bond energy Ehb, the degree of “cross-linking/atom” Pp and the radial bond strength were determined.The correlation between the composition and properties of the Ag2Te-As2Se3-CdTe glasses was established and comprehensively discussed. 相似文献
3.
Infrared reflection and transmission measurements in AsχTe1?χ glasses (45?×?55) show well-defined Gaussian vibrational absorption peaks. Comparisons with spectra observed in crystalline and glassy As2S3 and As2Se3 indicate that the local order in AsχTe1?χ glasses is not like that found in crystalline As2Te3, but rather it consists primarily of AsTe3 pyramids which are probably linked together in a fashion similar to that found in As2S3 and As2Se3. 相似文献
4.
Qiuhua Nie Xunsi Wang Shixun Dai Shengwei Deng Tiefeng Xu Xiang Shen 《Optics Communications》2010,283(20):4004-4007
A new family of Tellurium-based glasses GeTe4-Ga2Te3-AgX (X = I/Br/Cl) has been investigated and the glass-forming region was determined. Properties measurements include XRD, DTA, vis-NIR, and IR transmission spectra. The amorphous nature of the glasses has been proved by X-ray diffraction. Among the three systems, the GeTe4-Ga2Te3-AgI glass system shows superior glass-forming ability and thermal stability. The maximum value of ΔT (= Tx − Tg) lies at about 110 °C for the glass composition 60GeTe4-2-20Ga2Te3-20AgI, while for 60GeTe4-20Ga2Te3-20AgBr and 60GeTe4-20Ga2Te3-20AgCl, the ΔT values are both only 88 °C. Most of the studied glasses have a wide optical transmission window from 1.8 to 25 μm. 相似文献
5.
Temperature and frequency dependence of dielectric constant (ε′) and dielectric loss (ε″) are studied in glassy Se70Te30 and Se70Te28Zn2. The measurements have been made in the frequency range (8-500 kHz) and in the temperature range 300 to 350 K. An analysis of the dielectric loss data shows that the Guintini's theory of dielectric dispersion based on two-electron hopping over a potential barrier is applicable in the present case.No dielectric loss peak is observed in glassy Se70Te30. However, such loss peaks exist in the glassy Se70Te28Zn2 in the above frequency and temperature range. The Cole-Cole diagrams have been used to determine some parameters such as the distribution parameter (α), the macroscopic relaxation time (τ0), the molecular relaxation time (τ) and the Gibb's free energy for relaxation (ΔF). 相似文献
6.
H.E. Atyia 《Physica B: Condensed Matter》2008,403(18):3130-3136
Se85Te10Bi5 films of different thicknesses ranging from 126 to 512 nm have been prepared. Energy-dispersive X-ray (EDX) spectroscopy technique showed that films are nearly stoichiometric. X-ray diffraction (XRD) measurements have showed that the Se85Te10Bi5 films were amorphous. Electrical conduction activation energy (ΔEσ) for the obtained films is found to be 0.662 eV independent of thickness in the investigated range. Investigation of the current voltage (I-V) characteristics in amorphous Se85Te10Bi5 films reveals that it is typical for a memory switch. The switching voltage Vth increases with the increase of the thickness and decreases exponentially with temperature in the range from 298 to 383 K. The switching voltage activation energy (ε) calculated from the temperature dependence of Vth is found to be 0.325 eV. The switching phenomenon in amorphous Se85Te10Bi5 films is explained according to an electrothermal model for the switching process. The optical constants, the refractive index (n) and the absorption index (k) have been determined from transmittance (T) and reflectance (R) of Se85Te10Bi5 films. Allowed non-direct transitions with an optical energy gap (Egopt) of 1.33 eV have been obtained. ΔEσ is almost half the obtained value of Egopt, which suggested band to band conduction as indicated by Davis and Mott. 相似文献
7.
Superconductivity and non-metallicity induced by doping the topological insulators Bi2Se3 and Bi2Te3
Y.S. Hor J.G. Checkelsky D. Qu R.J. Cava 《Journal of Physics and Chemistry of Solids》2011,72(5):572-576
We show that by Ca doping the Bi2Se3 topological insulator, the Fermi level can be fine tuned to fall inside the band gap and therefore suppresses the bulk conductivity. Non-metallic Bi2Se3 crystals are obtained. On the other hand, the Bi2Se3 topological insulator can also be induced to become a bulk superconductor, with Tc∼3.8 K, by copper intercalation in the van der Waals gaps between the Bi2Se3 layers. Likewise, an as-grown crystal of metallic Bi2Te3 can be turned into a non-metallic crystal by slight variation in the Te content. The Bi2Te3 topological insulator shows small amounts of superconductivity with Tc∼5.5 K when reacted with Pd to form materials of the type PdzBi2Te3. 相似文献
8.
Results of differential scanning calorimetry of high purity GexAs40−xSe40Te20 (x=0-40) chalcogenide glasses are reported. The glass transition temperatures and crystallization behavior were studied under non-isothermal conditions at different heating rates (2.5-35 K/min). The glass transition temperature changes from 140 °C up to 320 °C with increasing the Ge content in GexAs40−xSe40Te20 glass. The studied glasses with x≤35 have no exothermal peaks of crystallization, indicating their high glass-forming ability. The glass of Ge40Se40Te20 composition has one-stage glass transition and double-stage crystallization process during phase change. The activation energy of the glass transition (Eg), the activation energy of crystallization (Ec), the Avrami exponent (n), the frequency factor (K0) and the crystallization criteria of Ge40Se40Te20 glass were determined. 相似文献
9.
The effects of Cr doping on Mn sites in the electron-doped manganites La0.9Te0.1MnO3 have been studied by preparing the series La0.9Te0.1Mn1−xCrxO3 (0.05≤x≤0.20). Upon Cr doping, both the Curie temperature TC and magnetization M are suppressed. The resistivity measurements indicate that there exists a weak metal-insulator (M-I) transition for the sample with x=0.05, with an increase in the doping level, the M-I transition disappears and the resistivity increases. Thermopower S(T) exhibits a maximum near TC for all samples. By fitting the S(T) and ρ(T) curves, it is found that the temperature dependences of both S(T) and ρ(T) in the high temperature paramagnetic (PM) region follow the small polaron conduction (SPC) mechanism for all samples. The fitting parameters obtained imply changes of both the average-hopping distance of the polarons and the polaron concentration with Cr doping in our studied samples. In the case of the thermal conductivity κ(T), the variation of κ(T) is analyzed based on the combined effects due to the suppression of the local Mn3+O6 Jahn-Teller (JT) lattice distortion because of the substitution of Cr3+ for Mn3+ ions, which results in the increase in κ, and the introduction of the disorder due to Cr-doping, which contributes to the decrease in κ. 相似文献
10.
Bismuth selenotelluride (Bi2(Te0.9Se0.1)3) films were electrodeposited at constant current density from acidic aqueous solutions with Arabic gum in order to produce thin films for miniaturized thermoelectric devices. X-ray fluorescence spectroscopy determined film compositions. X-ray diffraction pattern shows that the films as deposited are polycrystalline, isostructural to Bi2Te3 and covered by crystallites. Mueller-matrix analysis reveals that the electroplated layers are optically like an isotropic medium. Their pseudo-dielectric functions were determined using mid-infrared spectroscopic ellipsometry. Tauc-Lorentz combined with Drude dispersion relations were successfully used. The energy band gap Eg was found to be about 0.15 eV. Moreover, the fundamental absorption edge was described by an indirect optical band-to-band transition. From Seebeck coefficient measurement, films exhibit n-type charge carrier and the value of thermoelectric power is about −40 μV/K. 相似文献
11.
Electrical conductivity and thermopower measurements are reported for the defect semiconductors p-In2Te3 and n-Ga2Te3. The hole mobility μp in the former varied as Tnwheren=+5.98 forT<350 K and n=-4.13 forT>350 K showing a maximum of 210 cm2V-1 sec-1 at 350 K. Electron mobility in n-Ga2Te3 also went through a maximum at 320 K. The optical band-gaps for both were found to be direct, with values of 1.01 and 1.08 eV for In2Te3 and Ga2Te3 respectively at 300 K. Pronounced effects of annealing on TEP and optical absorption gave evidence of defect ordering at low temperatures followed by defect creation at T>350 K. 相似文献
12.
A.S SoltanA.A Abu-Sehly M.A Abdel-Rahim 《Journal of Physics and Chemistry of Solids》2002,63(5):801-809
The optical absorption of the as-prepared and thermally annealed Se85−xTe15Sbx (0≤x≤9) thin films was measured. The mechanism of the optical absorption follows the rule of non-direct transition. The optical energy gap (E0) decreased from 1.12 to 0.84 eV with increasing Sb content of the as-prepared films from 0 to 9 at.%. The as-prepared Se76Te15Sb9 films showed an increase in (E0) with increasing the temperature of annealing in the range above Tg (363 K). The electrical conductivity of the as-prepared and annealed films was found to be of Arrhenius type with temperature in the range 300-360 K. The activation energy for conduction was found to decrease with increasing both the Sb content and temperature of annealing. The results were discussed on the basis of the lone-pair electron effect and of amorphous crystalline transformation. 相似文献
13.
The electrochemical reduction processes on stainless-steel substrates from an aqueous electrolyte composed of nitric acid, Bi3+, HTeO2+, SbO+ and H2SeO3 systems were investigated using cyclic voltammetry. The thin films with a stoichiometry of Bi2Te3, Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 have been prepared by electrochemical deposition at selected potentials. The structure, composition, and morphology of the films were studied by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM) and electron microprobe analysis (EMPA). The results showed that the films were single phase with the rhombohedral Bi2Te3 structure. The morphology and growth orientation of the films were dependent on the deposition potentials. 相似文献
14.
Thermoelectric films of n-Bi2Te3−ySey were prepared by potentiostatic electrodeposition technique onto stainless steel and gold substrates at room temperature. These films were used for morphological, compositional and structural analysis by environment scanning electron microscope (ESEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The effect of different substrates on the structure and morphology of Bi2Te3−ySey films and relation between Se content in the electrodepositing solutions and in the films were also investigated. These studies revealed that Bi, Te and Se could be co-deposited to form Bi2Te3−ySey semiconductor compound in the solution containing Bi3+, HTeO2+ and H2SeO3. The morphology and structure of the films are sensitive to the substrate material. The doped content of Se element in the Bi2Te3−ySey compound can be controlled by adjusting the Se4+ concentration in the electrodepositing solution. X-ray diffraction analysis indicates that the films prepared at −40 mV versus saturated calomel electrode (SCE) exhibit strong (1 1 0) orientation with rhombohedral structure. 相似文献
15.
X-irradiation of glassy As2O3 at 77K or 300K produces an unusually large density (~5×1018 cm-3) of paramagnetic centers which are stable at 300K. The average spin-Hamiltonian parameters (g = 1.998, g⊥ = 1.984, A6 = 243G, A⊥ = 114G) indicate that these centers are analogous to those previously observed in As2Se3 and As2S3 glasses and that they consist of unpaired electrons localized on a non-bonding 4p orbital of an As atom. Unlike the results obtained for As2Se3 and As2S3, the concommitant holes in As2O3 are trapped on Fe2+ impurity sites which become Fe3+ and not on non-bonding oxygen p orbitals. The radiation induced ESR is also accompanied by a stable optical absorption tail which lies within the band gap and increases exponentially with energy. This absorption can be partially bleached with the application of sub-band-gap light. 相似文献
16.
The pressure dependence of the thermoelectric power of monoclinic As2Te3 is measured up to 10 GPa using a Mao-Bell diamond anvil cell. The thermoelectric power never reaches an absolute value greater than the ambient pressure value of 242 μV/K. Evidence of a phase transition is present between 6 and 8 GPa where the thermoelectric power reaches an absolute value of 225 μV/K after passing through a minimum of S≈75 μV/K. X-ray diffraction experiments confirm that the resulting structure is β-As2Te3, which is isostructural with Bi2Te3 and Sb2Te3. 相似文献
17.
Electroreflectance measurements in Bi2Te3 and Bi2Se3 with the electric field vector of the incident light both inclined and perpendicular to the C-axis have been made at room temperature. The structures found by other workers in the reflection measurements are observed in the present experiment, together with new structures at 0.91 eV, 1.18 eV, 1.78 eV, and 2.61 eV in Bi2Se3 which are not related to formerly observed transitions. From these measurements, the selection rules for direct optical transitions in Bi2Te3 and Bi2Se3 are studied. Thermoreflectance measurements are also made at both room and liquid-nitrogen temperatures. The positions of the peaks obtained in the present work are compared with the electroreflectance and reflection data. 相似文献
18.
W.W. Warren G.F. Brennert E. Buehler J.H. Wernick 《Journal of Physics and Chemistry of Solids》1974,35(9):1153-1157
Differential thermal analysis and X-ray diffraction studies of the system Ga2(SexTe1?x)3 are reported and correlated with measurements of the electrical conductivity in the liquid state. The experiments reveal that Ga2Te3 and Ga2Se3 do not form a continuous series of pseudo-binary solid solutions but exhibit solid state immiscibility in the range 0.50 ? x ? 0.90. The composition dependence of the conductivity of the liquid alloys exhibits structure in the range of the solid state phase separation. Such “memory” in the liquid of a solid phase separation has not been reported previously and suggests the importance of concentration fluctuations in determining the electronic properties of the liquid alloys. 相似文献
19.
Anomalous X-ray scattering experiments for glassy room-temperature superionic conductors (As2Se3)0.4 (AgI)0.6 and (As2Se3)0.4(AgBr)0.6 were performed close to the As, Se, Ag, and Br K edges using a third-generation synchrotron radiation facility, ESRF. The differential structure factors, ΔiS(Q), were obtained from detailed analyses, indicating that ΔAsS(Q) and ΔSeS(Q) of both the glassy superionic semiconductors are similar to those of glassy As2 Se3 except the prepeak in ΔSeS(Q). The ΔAgS(Q) spectrum of (As2Se3)0.4 (AgI)0.6 looks molten salt-like. However, the ΔAg S(Q) of (As2Se3)0.4(AgBr)0.6 glass have quite different features from that of (As2Se3)0.4 (AgI)0.6 glass in the low Q range, and the ΔBrS(Q) has even a pre-shoulder around 13 nm? 1 unlike molten salts. In the differential pair distribution functions Δig(r) obtained from the Fourier transforms of ΔiS(Q), the first peaks of ΔAsg(r) and ΔSeg(r) show no correlation with those of ΔAgg(r) and ΔBrg(r), and vice versa. From these results, it can be concluded that a pseudo-binary mixture of the As2Se3 network matrix and AgX-related ionic conduction pathways is a good structural model for these superionic glasses. Differences between the AgBr- and AgI mixtures were found in the second-neighbor structures around the Ag atoms, which may reflect those in the crystal structures of the AgX salts. 相似文献
20.
A.A Abu-SehlyM.I Abd-Elrahman 《Journal of Physics and Chemistry of Solids》2002,63(1):163-170
The optical absorption of the As-prepared and annealed As45.2Te46.6In8.2 thin films are studied. Films annealed at temperatures higher than 453 K show a decrease in the optical energy gap (Eo). The value of Eo increases from 1.9 to 2.43 eV with increasing thickness of the As-prepared films from 60 to 140 nm. The effect of thickness on high frequency dielectric constant (?∞) and carrier concentration (N) is also studied. The crystalline structures of the As45.2Te46.6In8.2 thin films resulting from heat treatment of the As-prepared film at different elevated temperatures is studied by X-ray diffraction. An amorphous-crystalline transformation is observed after annealing at temperatures higher than 453 K. The electrical conductivity at low temperatures is found due to the electrons transport by hopping among the localized states near the Fermi level. With annealing the films at temperatures higher than 473 K (the crystallization onset temperature) for 1 h, the electrical conductivity increases and the activation energy decreases, which can be attributed to the amorphous-crystalline transformations. 相似文献