Propriétés thermiques et optiques des verres du système Sb2S3–As2S3–Sb2Te3

Thermal and optical properties of glasses of the Sb₂S₃–As₂S₃–Sb₂Te₃ system. The glass-forming region of Sb₂S₃–As₂S₃–Sb₂Te₃ is very wide. The As₂S₃ compound supports the formation of prepared glasses and their stability. They have only one glass-transition temperature (T_g), which varies from 167 to 214 °C. It drops when the content of Sb₂Te₃ increases. This semi-metal compound supports the crystallization of glasses in several stages. Whereas the optical gap (E_g) increases with the content of As₂S₃ in the Sb₂S₃–As₂S₃ and Sb₂Te₃–As₂S₃ binary systems, it is practically constant in the ternary one on the cut with 20% of Sb₂Te₃, and is worth on average 1.04 eV.     

Kinetics of phase transition and thermal stability in Se80?x Te20Zn x (x?=?2, 4, 6, 8, and 10) glasses

Se_80?x Te₂₀Zn _x (x?=?2, 4, 6, 8, and 10) glasses have been prepared using conventional melt quenching technique. The kinetics of phase transformations (glass transition and crystallization) have been studied using differential scanning calorimetry (DSC) under non-isothermal condition at five different heating rates in these glasses. The activation energy of glass transition (E _t), activation energy of crystallization (E _c), Avrami exponent (n), dimensionality of growth (m), and frequency factor (K _o) have been investigated for the better understanding of growth mechanism using different theoretical models. The activation energy is found to be highly dependent on Zn concentration. The rate of crystallization is found to be lowest for Se₇₀Te₂₀Zn₁₀ glassy alloy. The thermal stability of these glasses has been investigated using various stability parameters. The values of these parameters were obtained using characteristic temperatures, such as glass transition temperature T _g, onset crystallization temperature T _c, and peak crystallization temperature T _p. In addition to this, enthalpy-released during crystallization has also been determined. The values of stability parameters show that the thermal stability increases with the increase in Zn concentration in the investigated glassy samples.     

Thermal coefficient of linear expansion of non-crystalline chalcogenides in the As-S-Se-Te-I system

The object of the paper is an investigation of the glasses of the (As₂S₃)_x(AsSe_0.5Te_0.5I)_100-x. type for 65≤;x≤;95, using methods of thermomechanical analysis. Values of the thermal coefficients of linear expansion in solid and visco-plastic phase were determined. it was shown that introducing arsenic-sulfide in glass-matrix AsChI, i.e. (AsSe_0.5Te_0.5I), leads to an increasing stability of these glasses. The characteristic temperatures of softening Tg and the temperature of the beginning of deformation t_w increase by increasing content of As₂S₃. The analytical forms of dependence of four significant physical values α_g, α_l, Tg, Tw, as a function of As₂S₃ content in the structure of glasses were fitted. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-isothermal crystallisation kinetics study on Se90−xIn10Sbx (x = 0, 1, 2, 4, 5) chalcogenide glasses

The non-isothermal crystallisation kinetics of Se_90?xIn₁₀Sb_x (x = 0, 1, 2, 4, 5) chalcogenide glasses prepared by a conventional melt quenching technique was studied using the differential scanning calorimetry (DSC) measurement at different heating rates 5, 7, 10 and 12 °C min^?1. The values of the glass transition temperature T _g and the crystallisation temperature T _c are found to be composition and heating rate dependent. The activation energy of glass transition E _g, Avrami index n, dimensionality of growth m and activation energy of crystallisation E _c have been determined from different models.     

Interactions and glass formation in the TlAs2Se4-Tl3As2Se3Te3 system

The TlAs₂Se₄-Tl₃As₂Se₃Te₃ system was studied using differential thermal analysis (DTA), powder X-ray diffraction, microstructure observation, and microhardness and density measurements. A phase diagram of the title system was constructed. This system is a quasi-binary join of the TlSe-As₂Se₃-As₂Te₃ quasi-ternary system. All alloys of the system under standard conditions are prepared in the glassy form. The system has a eutectic, which contains 50 mol % Tl₃As₂Se₃Te₃ and melts at 150°C. The TlAs₂Se₄-base solid solution in the system extends to 12 mol % Tl₃As₂Se₃Te₃, and Tl₃As₂Se₃Te₃-based solid solution extends to 20 mol % TlAs₂Se₄.     

Determination of thermal parameters of glasses from the system Bix(As2S3)100?x based on DSC curves

Thermal properties of glasses from the system Bi _x (As₂S₃)_100−x were studied by differential scanning calorimetry of a representative series of samples with x = 0.5, 2, 4, 6, 8, and 10 at.% Bi by determining the characteristic temperatures (T _g, T _onset, T _c, T _m) and enthalpies (H _c, H _m) of the processes taking place in the samples during their thermal treatment. Analysis of DSC recordings for the samples at the same heating rate allowed characterization of the phase transition temperature T _g as a function of the content of doping atoms in accordance with the criteria of chemical bonds formation in amorphous materials. Samples with 4 and 6 at.% Bi were thermally treated at different heating rates with the aim of determining, among the others, the parameters of their thermal stability. The assessment was done based on three different criteria. A higher tendency toward crystallization was observed with the glasses having a higher Bi content. Also, a trend of T _g shifting toward higher values, observed with increase in the heating rate, is in concordance with the Lasocka equation.     

Thermal stability and crystallization kinetics of ternary Se–Te–Sb semiconducting glassy alloys

This paper presents the results of kinematical studies of glass transition and crystallization in glassy Se_85?x Te₁₅Sb _x (x = 2, 4, 6 and 8) using differential scanning calorimetry (DSC). From the dependence on heating rates of, the glass transition temperatures (T _g), and temperature of crystallization (T _p) the activation energy for glass transition (E _g) and the activation energy for crystallization (E _c) are calculated and their composition dependence can be discussed in term of the average coordination number and cohesive energy. The thermal stability of Se_85?x Te₁₅Sb _x was evaluated in terms of criterion ΔT = T _c ? T _g and kinetic criteria K(T _g) and K(T _p). By analyzing the crystallization results, the crystallization mechanism is characterized. Two (two- and three-dimensional growth) mechanisms are working simultaneously during the amorphous–crystalline transformation of the Se₈₃Te₁₅Sb₃ alloy while only one (three-dimensional growth) mechanism is responsible for the crystallization process of the chalcogenides Se_85?x Te₁₅Sb _x (x = 4, 6 and 8) glass. The phases at which the alloy crystallizes after the thermal process have been identified by X-ray diffraction.     

The kinetics of phase transitions in vitreous chalcogenide semiconductors As10.2Se89.8 and As9Se90Bi in early stage of physical ageing process

The kinetics of glass transition in selenide glasses As_10.2Se_89.8 and As₉Se₉₀Bi in early stage of physical ageing process has been investigated by parallel differential scanning calorimetry (DSC) and exoelectron emission (EEE). It has been found that the glass transition process occurring in investigated glasses is evidenced by peaks on EEE intensity and DSC curves. Admixture of bismuth causes a distinct lowering of the temperature of glass transitions process both in the surface layer and in the volume. The addition of Bi causes a decrease in the value of the activation energy for glass transition process in both the volume and in the surface layer, thus reducing the thermal stability of investigated glasses. Physical ageing in Se-rich chalcogenide glasses leads to a significant increase of endothermic peak area A, temperature of glass transition T _g and decrease of the activation energy value E. All these effects are strongly dependent on glass composition.     

Effect of in impurity on crystallization kinetics of (Se.7Te.3)100−xInx system

The effect of In impurity on the crystallization kinetics and the changes taking place in the structure of (Se₇Te₃) have been studied by DTA measurements at different heating rates (α=5 deg·min^?1, 10 deg·min^?1, 15 deg·min^?1 and 20 deg·min^?1). From the heating rate dependence of the values ofT _g,T _c andT _p, the glass transition activation energy (E _t) and the crystallization activation energy (E _c) have been obtained for different compositions of (Se₇Te₃)_100?xIn_x (0≤×≤20). The variation of viscosity as a function of temperature has been evaluated using Vogel-Tamman-Fulcher equation. The crystallization data are analysed using Kissinger's and Matusita's approach for nonisothermic crystallization. It has been found that for samples containing In=0, 10, 15, 20 at%, three dimensional nucleation is predominant whereas for samples containing In=5 at%, two dimensional nucleation is the dominant mechanism. The compositional dependence ofT _g and crystallization kinetics are discussed in terms of the modification of the structure of the Se?Te system.     

Phase equilibria and glass formation in the As2S3-TlAs2S2Se2 section of the As2S3-As2Se3-TlS system

Alloys in the As₂S₃-TlAs₂S₂Se₂ section of the As₂S₃-As₂Se₃-TlS ternary system were studied and a phase diagram was constructed using physicochemical methods (differential thermal analysis, microstructural analysis, X-ray powder diffraction, also microhardness and density measurements). The diagram in the As₂S₃-TlAs₂S₂Se₂ section is a non-quasi-binary diagonal section of the As₂S₃-As₂Se₃-TlSe quasi-ternary system. It was found that all the alloys in the section under ordinary conditions are obtained in the vitreous state. At low As₂S₃ concentrations in the section, solid solutions form up to 2.5 mol %, and at low TlAs₂S₂Se₂ concentrations, their extent is 3 mol %.     

Conductibilité electrique aux basses températures des composés binaires Cr2X3 et Cr3X4 (X = S,Se ou Te)

Electrical resistivity of some binary compounds Cr₂X₃ and Cr₃X₄ (X = S, Se or Te) is studied on polycrystalline samples with the four point probe method, at temperatures between 4.2 and about 330 K. A metallic behavior is observed on Cr₂Te₃, Cr₃Te₄, Cr₃S₄ and the 3c′ form of Cr₂Se₃. Some other compounds are semiconductors: Cr₃Se₄ (E_300K ≈ 0.07 eV; E_4.2K = 2.07 × 10^?4 eV), the 2c′ form of Cr_2+εSe₃ (E_300K ≈ 0.074 eV; E_4.2K = 2.76 × 10^?4 eV) and the 3c′ form of Cr₂S₃ (E_275K ≈ 0.55 eV). The observed results seem to be closely related to the nature of the octahedral neighborhood of the cations.     

Thermal behaviour and excess entropy of bioactive glasses and Zn-doped glasses

Bioactive glasses prepared in SiO₂–CaO–Na₂O and P₂O₅ system are used as biomaterials in orthopaedic and maxillofacial surgery. Zn presents high physiological interest. It enhances physiological effects of implanted biomaterials. In this work, the thermal characteristics (T _g, T _c and T _f) of pure bioactive glass elaborated with different amounts of CaO, Na₂O in pure glass and with different amounts of introduced Zn in glass (ranging from 0.1 to 10 in mass%), were studied. The excess entropy was calculated for different compounds. Glasses were prepared by the melting process. The thermal behaviour of obtained bioactive glasses was determined using differential thermal analysis. Therefore, the glass transition (T _g), the crystallization (T _c) and the melting temperatures (T _f) were revealed. Moreover, according to Dietzel formula, the thermal stability (TS) of the studied bioactive glasses has been calculated. The first results concerning the impact of different oxides, revealed a decrease of the TS, T _g, T _c and T _f when the SiO₂/CaO increases and revealed an increase of these thermal characteristics when the SiO₂/Na₂O and CaO/Na₂O ratios increase. Introducing Zn into the bioactive glasses induces a decrease of T _f and an increase of TS. Contrary to crystals, prepared glasses have entropy different to zero at T = 0 K and vary versus T _f. The excess entropy of pure glasses and Zn-doped glasses were calculated. The significant variations were registered.     

Phase equilibria in the Ag4SSe–As2Se3 system

The phase diagram of the system Ag₄SSe–As₂Se₃ is studied by means of X-ray diffraction, differential thermal analyses and measurements of the microhardness and the density of the materials. The unit-cell parameters of the intermediate phases 3Ag₄SSe·As₂Se₃ (phase A) and Ag₄SSe·2As₂Se₃ (phase B) are determined as follows for phase A: a=4.495 Å, b=3.990 Å, c=4.042 Å, α=89.05°, β=108.98°, γ=92.93°; for phase B: a=4.463 Å, b=4.136 Å, c=3.752 Å, α=118.60°, β=104.46°, γ=83.14°. The phase 3Ag₄SSe·As₂Se₃ and Ag₄SSe·2As₂Se₃ have a polymorphic transition α?β consequently at 105 and 120°C. The phase A melts incongruently at 390°C and phase B congruently at the same temperature.     

Serendipitous syntheses of the series Cs3Ln7Te12 (Ln = Sm,Gd, Tb): Compounds with large tunnels

Single crystals of Cs₃Ln₇Te₁₂ (Ln = Sm, Gd, Tb) have been grown accidentally through the reaction of Ln and Te with a CsCl or Cs₂Te₃ flux at elevated temperatures. The crystal structures have been determined from single crystal X-ray diffraction data. These compounds, which are isostructural with Rb₃Yb₇Se₁₂, crystallize in space group Pnnm of the orthorhombic system with two molecules in the following cells: Cs₃Sm₇Te₁₂, a=13.750(6), b=28.332(7), c=4.473(3) Å, T=293 K; Cs₃Gd₇Te₁₂, a=13.6064(13), b=28.209(3), c=4.4324(4) Å, T=153 K; Cs₃Tb₇Te₁₂, a=13.5708(16), b=28.116(3), c=4.4147(5) Å, T=153 K.     

Laser Desorption Ionization of As<Subscript>2</Subscript>Ch<Subscript>3</Subscript> (Ch = S,Se, and Te) Chalcogenides Using Quadrupole Ion Trap Time-of-Flight Mass Spectrometry: A Comparative Study

Laser desorption ionization using time-of-flight mass spectrometer afforded with quadrupole ion trap was used to study As₂Ch₃ (Ch = S, Se, and Te) bulk chalcogenide materials. The main goal of the study is the identification of species present in the plasma originating from the interaction of laser pulses with solid state material. The generated clusters in both positive and negative ion mode are identified as 10 unary (S _p ^+/– and As _m ^+/– ) and 34 binary (As _m S _p ^+/– ) species for As₂S₃ glass, 2 unary (Se _q ^+/– ) and 26 binary (As _m Se _q ^+/– ) species for As₂Se₃ glass, 7 unary (Te _r ^+/– ) and 23 binary (As _m Te _r ^+/– ) species for As₂Te₃ material. The fragmentation of chalcogenide materials was diminished using some polymers and in this way 45 new, higher mass clusters have been detected. This novel approach opens a new possibility for laser desorption ionization mass spectrometry analysis of chalcogenides as well as other materials.

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Effect of Bi incorporation on the glass transition kinetics of Se<Subscript>85</Subscript>Te<Subscript>15</Subscript> glassy alloy

Bulk samples of Se_85-xTe₁₅Bi_x glassy alloys are obtained by melt quenching technique. Differential scanning calorimetry has been applied to determine the thermal properties of Se-rich Se_85-xTe₁₅Bix glassy alloys at different heating rates. The glass transition temperature (T _g) is found to shift to a higher temperature with increasing heating rate and with Bi addition. Activation energy and fragility of the system is also calculated. Specific heat is evaluated and a jump in heat capacity is observed at T _g. Theoretical parameters viz; density, molar volume, number of atoms per unit volume, lone pair electrons and cohesive energy of the system are also reported.     

Effect of MoO<Subscript>3</Subscript> additions on the thermal stability and crystallization kinetics of PbO–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–As<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The present paper reports on the effect of MoO₃ on the glass transition, thermal stability and crystallization kinetics for (40PbO–20Sb₂O₃–40As₂O₃)_100−x –(MoO₃) _x (x = 0, 0.25, 0.5, 0.75 and 1 mol%) glasses. Differential scanning calorimetry (DSC) results under non-isothermal conditions for the studied glasses were reported and discussed. The values of the glass transition temperature (T _g) and the peak temperature of crystallization (T _p) are found to be dependent on heating rate and MoO₃ content. From the compositional dependence and the heating rate dependence of T _g and T _p, the values of the activation energy for glass transition (E _g) and the activation energy for crystallization (E _c) were evaluated and discussed. Thermal stability for (40PbO–20Sb₂O₃–40As₂O₃)_100−x –(MoO₃) _x glasses has been evaluated using various thermal stability criteria such as ΔT, H _r , H _g and S. Moreover, in the present work, the K _r(T) criterion has been considered for the evaluation of glass stability from DSC data. The stability criteria increases with increasing MoO₃ content up to x = 0.5 mol%, and decreases beyond this limit.     

Mischkristalle aus A4B3-Molekülen (A = P,As; B = S,Se)

Mixed Crystals from A₄B₃ Molecules (A = P, As; B = S, Se) The system P₄S₃? P₄Se₃? As₄S₃? As₄Se₃ was investigated by thermal and x-ray methods. Five regions of solid solubility with different crystal structures were found at room temperature. The range of existence can be influenced by the temperature of annealing. All these phases transform into a plastic-crystalline modification with complete solid solubility at higher temperature. A decomposition reaction of the A₄B₃ molecules was observed in the P₄Se₃/As₄Se₃/As₄S₃ part of the system. The molecules decompose into A₄B₄ molecules and an amorphous phase. The existence of all molecules of the type P_nAs_4–nS_mSe_3–m (n = 0–4, m = 0–3) and also As₄S_mSe_4–m (m = 1–3) was verified by mass spectrometric measurements. The thermochemical data of the mixed crystals are determined by the type of the constituent A₄B₃ molecules. The temperature and the entropy of the α–β transition are lower for mixed crystals, formed by substituted molecules, than for those of the same structure, consisting of pure A₄B₃ molecules.     

Glass-forming ability and thermal stability of Se<Subscript>100−x</Subscript>(Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript>)<Subscript>x</Subscript> glassy alloys

Glassy Se_100?x(Ge₂Sb₂Te₅)_x (x?=?5, 10, 15 and 20) bulk alloys were prepared by melt-quenched technique and studied by using differential scanning calorimetry at different heating rates under non-isothermal condition. The detailed thermal analysis shows that the glass transition temperature (T_g) depends on heating rates and x content. In particular, it is found that the glass-forming ability, thermal stability (T_c???T_g) and crystallization activation energy (E_c) increase with increased x content in amorphous Se, whereas glass transition activation energy (E_g) and fragility index (F) decrease with increased x contents. Variation in these parameters can be explained on the basis of network-forming ability of Se and bonding arrangement among the constituent atoms of alloys.     

Laser ablation of ternary As‐S‐Se glasses and time‐of‐flight mass spectrometric study

Ternary chalcogenide As‐S‐Se glasses, important for optics, computers, material science and technological applications, are often made by pulsed laser deposition (PLD) technology but the plasma composition formed during the process is mostly unknown. Therefore, the formation of clusters in a plasma plume from different glasses was followed by laser desorption ionization (LDI) or laser ablation (LA) time‐of‐flight mass spectrometry (TOF MS) in positive and negative ion modes. The LA of glasses of different composition leads to the formation of a number of binary As_pS_q, As_pSe_r and ternary As_pS_qSe_r singly charged clusters. Series of clusters with the ratio As:chalcogen = 3:3 (As₃S, As₃S₂Se⁺, As₃SSe), 3:4 (As₃S, As₃S₃Se⁺, As₃S₂Se, As₃SSe, As₃Se), 3:1 (As₃S⁺, As₃Se⁺), and 3:2 (As₃S, As₃SSe⁺, As₃Se), formed from both bulk and PLD‐deposited nano‐layer glass, were detected. The stoichiometry of the As_pS_qSe_r clusters was determined via isotopic envelope analysis and computer modeling. The structure of the clusters is discussed. Copyright © 2009 John Wiley & Sons, Ltd.