Ge Se Glasses Research Articles

Influence of vapor-phase reaction on the reduction of OH?and S–H absorption bands in GeS2-based glasses for infrared optics

The reduction of OH- and S–H absorption bands in unary and ternary germanium sulphide glasses with oxides and hydroxides present in the raw materials and in impure glasses was studied via the chemical reaction of H2and HCl gases at high temperatures. Multicomponent phase equilibria calculations in the Ge–S–H–O–X (X = Cl, I) system were performed to determine the equilibrium partial pressures of gaseous species for removing oxygen and hydrogen from the glasses used for infrared (IR) applications. The effect of carbon on the reduction in oxide and hydroxide absorption bands was also investigated. The absorption characterization was carried out using a Fourier transform infrared reflection spectrophotometer. The IR absorption bands between 1000 and 3700 cm-1 were identified and analyzed. The Boson peaks (BP) in glass samples with two different OH- concentrations were also analyzed. It was found that the presence of OH- enhanced the intensity of Boson peaks. The sites for OH- and shared oxygen with the main [GeS4] 4- tetrahedron structural units in the glass are discussed with respect to the BP and IR absorption analyses. The structure model also identifies the origin of the reduced Rare-earth (RE+3 ) ion solubility (in particular Pr 3+ ions) and its dependence on OH- ion concentrations in GeS2 glasses

The structural origin of broken chemical order in GeSe2 glass

Abstract Raman scattering, 119Sn Mössbauer spectroscopy and temperature-modulated differential scanning calorimetry experiments have been performed on (Ge0.99 Sn0.01)x Se1−x glasses in the 0.30 < x < 0.36 range. Both Raman and Mössbauer spectroscopies show that Ge‒Ge signatures first appear near x = 0.31(1), and their concentration slowly increases with increasing x to acquire a value of 1.92(30)% at x = 1/3, corresponding to GeSe2 glass. Thereafter (1/3 < x < 0.36) the concentration of these bonds increases precipitously with increasing x. Glass transition temperatures T g(x) reflect the connectivity of the network and are found to increase with increasing x; however, the rate dTg/dx of T g increase slows down markedly at (i) x ≥ 0.31(1), and the rate actually reverses sign (ii) at x ≥ 0.34. Feature (i) coincides with nucleation and (ii) with precipitous growth of Ge‒Ge signatures. These T g trends show that the presence of Ge‒Ge signatures decreases the global connectivity of the glasses. The results unequivocally demonstrate that the Ge‒Ge bonds constitute part of a marginally rigid Ge2(Se1/2)6-bearing nanophase that is formed separately from the Ge(Se1/2)4-tetrahedra-bearing backbone of the glasses.

A consistent approach towards Bi doping mechanism in chalcogenide glasses from Cp measurement in Ge–Se–Te–Bi system

In this paper, we are proposing a consistent approach to understand the mechanism of Bi doping in Ge–Se glasses by carrying out specific heat ( C p ) measurement in Ge 20Se 70− x Te 10Bi x system for 0≤ x≤11. The two softening temperatures exhibited by heat-treated samples are explained on the basis of ‘microscopic phase separation’. The minimum in ‘configurational heat capacity’ (Δ C p ) at x=7.5 for as-prepared glasses is related to be a feature of chemical threshold. A supporting evidence for three-fold coordination for Bi in line with the earlier structural studies is deduced.

Short-Range Order in Se-Rich Ge–Se Glasses—An Extended X-Ray Absorption Fine Structure Study

The short-range order in vitreous Ge1−xSex(2/3≤x≤1) at 80 K was studied by EXAFS spectroscopy at the Ge and Se K-edges. The results were analyzed using theoretical phase shift and amplitude functions and by comparison to crystalline GeSe2 and Se as model compounds. The GeSe4 tetrahedron is the main structural entity for all the Ge–Se alloys. The results indicate a slight increase in Ge coordination and a decrease in Se coordination with increasing Se content. Possible sources of error are discussed, and possible origins of the structural changes are suggested.

Structural Properties of GeSe2 at High Pressures

Crystalline and glassy GeSe2 have been subjected to pressures up to 7.7 GPa and temperatures up to 1100°C using a high-pressure belt-type apparatus. Two high-pressure crystalline polymorphs of GeSe2 have been synthesized. The crystal structure of the tetragonal form of GeSe2 prepared at 3.0 GPa and 500°C, with space group I-42d and a=5.7307(4) and c=9.691(1), was determined by means of powder X-ray diffraction data. The structure consists of GeSe4 tetrahedra that share corners in a three-dimensional network and has a considerably higher density than the two-dimensional structure of ambient-pressure GeSe2 consisting of both edge- and corner-sharing tetrahedra. The IR and Raman spectra of tetragonal GeSe2 are discussed in relation to the structure of GeSe2 glass. An orthorhombic polymorph of GeSe2 was formed during quenching from 7.7 GPa and 500°C. Amorphous GeSe2 compressed at 250–300°C was observed to partly crystallize at 3.0 and 7.7 GPa.

Photoconductivity and carrier lifetime in In/Bi doped Ge-Se glasses

Photoconducting properties of the GexSe100-x bulk semiconducting glass system are found to improve with the addition of indium or bismuth. In the GexIn5Se95-x system, appreciable variations in photoconductivity and carrier lifetime are found to occur at average atomic coordination numbers Z = 2.41 and 2.73. These are explained on the basis of the mechanical threshold and chemically ordered covalent network (COCN) models. In the Ge20BixSe80-x system, a sharp decrease in photoconductivity and carrier lifetime are observed at the composition corresponding to x = 7 (Z = 2.47), where a p-type to n-type transition has been reported earlier. Although differences in many of their properties do exist, Ge-Se, Ge-In-Se and Ge-Bi-Se systems remain type I photoconductors and their behaviour can be analysed in terms of the ABFH model.

Carrier type reversal in Bi doped GeSe glasses manifested in thermal transport measurements

It is known that Bi doped Ge-X glasses (X = S or Se) exhibit carrier type reversal from p-type to n-type at Bi content around 7 at.%. A careful measurement of the composition dependence of thermal diffusivity α by the photoacoustic (PA) phase lag technique reveals a threshold maximum in α occuring at around the same Bi content. Constraints model predicts criticality for such a system at the composition at which carrier type reversal and threshold maximum in α are observed.

Glass Transition Behavior in Se-Rich Ge-Se Alloys

Differential scanning calorimetry (DSC) was utilized to study the behavior of six Ge-Se glasses containing 0, 5, 10, 15, 17.5 and 20 at.% Ge during the glass transition. These alloys readily form glasses and can be prepared by quenching in air. Moreover, their behavior depends greatly on the composition. This work reveals that two additional properties must be considered: the variation in the glass transition temperature and different structural relaxation. The quantity used to quantify the relaxation was the enthalpy relaxation as this measures the heat lost by the glass during annealing. Given the complexity of the relaxation process, the experimental results were analysed by means of the empirical Kohlrausch-Williams-Watts relaxation model.

On the irreversible photo-bleaching phenomenon in obliquely-evaporated GeS2 glass films

On the irreversible photo-bleaching phenomenon in obliquely-evaporated GeS2 glass films

Glass transformation, heat capacity, and structure of GexSe100−x glasses studied by temperature-modulated differential scanning calorimetry experiments

The recent novel temperature-modulated differential scanning calorimetry (DSC) (MDSCTM TA Instruments) technique has been applied to characterize the thermal properties of Ge–Se chalcogenide glasses in the glass transition region. All samples in this work were given the same thermal history by heating to a temperature above the glass transition, equilibrating, and then cooling at a rate of 5 °C/min to a temperature of 20 °C. The reversing and nonreversing heat flows through the glass transformation region during both heating and cooling schedules were measured, and the values of the parameters Tg, ΔH, Cp, and ΔCp, which characterize the thermal events in the glass transition region, were determined. The ability of determining the reversible heat flow in MDSC enables an accurate measurement of the true heat capacity (that normally associated with reversible heat flow), which could not be done hitherto in conventional thermal analysis where the detected heat flow is the total heat flow, the sum of reversing and nonreversing heat flows. The structurally controlled parameters Tg, ΔH, Cp, and ΔCp reveal extrema when the Ge–Se glass system reaches the average coordination number 〈r〉 = 2.67 at 33.3 at.% Ge which corresponds to the stoichiometric composition GeSe2. We also observed extrema in the composition dependence of the above thermal parameters at 20.0 and 40.0 at.% Ge which correspond to stoichiometric compositions GeSe4 and Ge2Se3 with average coordination numbers 2.40 and 2.80, respectively. No such clear local maxima below and above the 33.3 at.% Ge composition could be observed previously in thermal analysis. We compare our MDSC results with previously published works on glass transition in Ge–Se glasses and discuss the results in terms of recent structural models for chalcogenide glasses.

Spectroscopic and Thermal Properties of GeS2-based chalcohalide glasses

The low phonon energy of germanium sulphide glasses makes them ideal candidates as hosts for 1.3µm fibre amplifier applications. However, the GeS2 glass host suffers from a major drawback of poor rare-earth ion solubility. In an efficient device, the solubility of Pr ions has to be enhanced, without adversely affecting either the thermal or the spectroscopic properties of the glass. In the present investigation, we report the synthesis and optical properties of modified GeS2-based chalcohalide glasses with excellent thermal characteristics suitable for drawing low-loss optical fibres.

Spectroscopic and thermal properties of GeS2-based chalcohalide glasses

Abstract The low phonon energy of germanium sulphide glasses makes them ideal candidates as hosts for 1·3 μm fibre amplifier applications. However, the GeS2 glass host suffers from a major drawback of poor rare-earth ion solubility. In an efficient device, the solubility of Pr ions has to be enhanced, without adversely affecting either the thermal or the spectroscopic properties of the glass. In the present investigation, we report the synthesis and optical properties of modified GeS2-based chalcohalide glasses with excellent thermal characteristics suitable for drawing low-loss optical fibres.

Structure and Optical Conductivity of Silver Thiogermanate Glasses

Silver thiogermanate glasses x AgI · (1 - x) [yAg2S · (1 - y) GeS2] were investigated by infrared reflectance and Raman spectroscopies to study the glass structure as a function of Ag2S (0 ≤ y ≤ 0.5) and AgI (y = 0.5, 0 ≤ x ≤ 0.375) content. The results for binary glasses indicate that addition of Ag2S to GeS2 glass induces the depolymerization of the thiogermanate network by creation of terminal Ge-S- bonds. AgI was also found to affect the network structure and this was expressed by disproportionation reactions. The interactions between Ag+ ions and their sites were also investigated and discussed in relation to the high ionic conductivity of these glasses. Broad range conductivity spectra were also obtained by combining dielectric and far-infrared conductivity data.

Charged defects-controlled conductivity in Ge-ln-Se glasses

The variation of the d.c. electrical conductivity, σ, with composition and temperature was investigated for glasses of the Ge-In-Se system. The results indicate a decrease in the activation energy for electrical conductivity, ΔE, and an increase in σ on introduction of indium into Ge-Se glasses. The changes in ΔE and σ with composition (selenium content in the glasses) are identical for the Gex In5 Se95−x and Gex In8Se92−x families. The results have been traced to the conduction controlled by charged defects in these chalcogenide glasses. The changes in ΔE and σ have been explained by a shift in the Fermi level, being brought by the introduction of indium.

Transmission electron microscopy of GeSe2+δ thin films

GeSe2 can exist in both amorphous and crystalline phases. Although most semiconductor devices are constructed from crystalline materials, the use of amorphous materials in devices has high potential. The study of GeSe2 is especially interesting since it has been established that an amorphous-to-crystalline transition can be induced by laser irradiation. In order to better understand this phenomenon, it is necessary to study the microstructure of GeSe2 glass. Therefore, transmission electron microscopy studies were undertaken to investigate the degree of crystallinity of GeSe2 glass. It was found that small microcrystallites with diameters in the range of 100–300 Å were embedded in a glass matrix. These microcrystallites formed larger clusters in some areas.

Scattering loss characteristics of selenide-based chalcogenide glass optical fibers

Scattering loss characteristics of Ge-Se binary chalcogenide glass optical fibers are investigated. It is found that there is a strong correlation between the wavelength-independent scattering loss and the absorption caused by H2O impurities. Therefore, the amount of H2O impurity mainly determines the wavelength-independent loss of these optical fibers. After removing the H2O impurity and adjusting the fabrication conditions, the transmission loss is less than 1 dB/m over a wide infrared wavelength region of 2–8.5 μm, except for a small peak at 4.5 μm.

Short and medium range order in germanium sulfide glasses: a low temperature X-ray absorption spectroscopy study

Ge K-edge EXAFS measurements were carried out at 35 K for GeSx (1.5 ≤ x ≤ 5) binary glasses and (1−y)GeS2 + yAg2S (0 ≤ y ≤ 0.4) glassy compositions. The three first Ge coordination shells were resolved. Thus, the short range order around germanium atoms located in tetrahedral sites has been confirmed. Then, knowledge of the medium range order existing in these glasses was improved, particularly on clustering of GeS4 tetrahedral units by edges or corners. Further, both the depolymerization rates of edge and corner sharing GeS4 tetrahedra have been estimated by reference to αGeS2 structure. The (g)GeS2 structure is mainly constituted by two-dimensional clusters based on αGeS2 crystalline structure. In this case the depolymerization fractions are both equal to about 40%. When the atomic composition deviates from the GeS2 stoichiometry for GeSx binary glasses, or when Ag2S is added to the GeS2 glass former, a significant increase of the depolymerization of both corner and edge linkages is noted. This increase implies an increase of the structural distortion in the local and mainly in the intermediate range order.

Structure of vitreous Ag [sbnd]Ge [sbnd]Se

Pulsed neutron diffraction has been used to study the short- and intermediate-range order of vitreous g-Ag4Ge3Se9. By utilizing the techniques of isotopic substitution and temperature variation, it has been possible to estimate four of the six partial pair-distribution functions for the first coordination shells. Measurements at T = 10 K extending out to wavevectors Q ≈ 34 Å−1 provide accurate results for the bond lengths and coordination numbers. Comparison is also made with results derived from a variant of the maximum entropy method. Ge is fourfold-coordinated by Se at an average interatomic distance of 2.37 ± 0.005 Å which is consistent with the GeSe4/2 tetrahedron also being a structural unit in the Ag-doped GeSe glass. Ag is predominantly bonded to Se at an average distance of 2.68±0.01 Å and is threefold-coordinated. This low coordination might be a key factor in understanding the fast ion motion in this system. The temperature dependence of the structure factor, S(Q), and the radial distribution functions were investigated. The GeSe and SeSe correlations solely reflect increased thermal vibrations of the atoms, whereas the Ag correlations behave quite differently with increasing temperature up to 170°C. The Ag correlations change rapidly and become liquid-like at elevated temperatures reflecting the diffusive motion of Ag. The first sharp diffraction peak at 1.04 Å−1 in S(Q) exhibits the anomalous temperature dependence typical of chalcogenide glasses in that the peak becomes narrower and increases in amplitude with increasing temperature (∼ 2% from room temperature to 170°C).

Enthalpy recovery in Se rich GeSe glasses during isothermal annealing and continuous heating

Structural recovery was measured calorimetrically in three GeSe glasses with 5, 10 and 15 at.% Ge. Accurate measurements of the apparent heat capacity below and through the glass transition were performed by differential scanning calorimetry. Careful analysis of the contribution of the irreversibility inherent to the glass transition allowed separation of the true heat capacity from the apparent heat capacity in the glass transition region. The quantity used to quantify the relaxation was the enthalpy relaxation as it measures the heat lost by the glass during the annealing. An accurate description of both iso- and non-isothermal measurements was obtained by the activation energy spectrum model.

Chalcogenide glasses Ge–Sn–Se, Ge–Se–Te, and Ge–Sn–Se–Te for infrared optical fibers

Chalcogenide glasses of the systems Ge–Sn–Se, Ge–Se–Te, and Ge–Sn–Se–Te have been prepared. Several compositions were found suitable for drawing fibers for CO2 laser radiation (λ = 10.6 μm) transmission. The glasses were characterized by x-ray diffraction, DSC (Differential Scanning Calorimetry), SEM with EDX analysis, FTIR spectrometry, density, and microhardness measurements. The glass transition temperature and microhardness of Ge–Se–Sn and Ge–Sn–Se–Te glasses decreased with increasing Sn content, for most of the samples. The region of high IR transparency of Ge–Se–Sn, Ge–Se–Te, and Ge–Sn–Se–Te glasses was slightly expanded (1–2 μm) toward longer wavelengths, compared to Ge–Se glasses, mainly for the glasses containing 70 at.% Se. The intensity of the impurity absorption peak of Ge–O (at λ ∼ 12.8 μm), which usually appears in Ge–Se glasses, was reduced or absent in Ge–Sn–Se–Te glasses. The best fibers were produced with the glass composition Ge–0.8Sn0.2Se3.5Te0.5. An attenuation of 20 dB/m at 10.6 μm, and a transmitted maximum power density of 2.4 ⊠ 106 W/m2 were measured. The mechanical and optical characteristics of these glasses have been related to the glasses structure. Corresponding to the reduced masses of the bonds formed in the Ge–Sn–Se–Te system (in the amorphous region), it is expected that the multiphonon edge is slightly shifted. As a consequence, as was measured, the transparency region has been expanded by less than 2 μm toward longer wavelengths.