Glass Transition Activation Energy Research Articles

Optical properties of annealed As30Te67Ga3 thin films grown by thermal evaporation

Chalcogenide glasses have received lots of attention because of their superior optical properties. To optimize these properties and expand areas of applications, more studies are required to establish the extent to which the parameters can be tuned over a wide range of annealing temperatures and heating rates. To do this, bulk and thin ?150 nm As30Te67Ga3 films were prepared by melt-quenching and thermal evaporation techniques, respectively. The phase transition was investigated using differential scanning calorimeter (DSC) while the crystal structures were studied by X-ray diffraction (XRD). Characteristic temperatures such as the glass transition, crystallization and melting temperature of the bulk glass were found to depend on the heating rate. The activation energy of glass transition was 167.29 kJ/mol while the energy of crystallization was 103.98 kJ/mol. XRD results indicated that the annealed films showed more crystallinity, larger average crystallite size, lower dislocation density and lower strain as annealing temperature increased. According to the Avrami exponent, a combination of two and three-dimensional crystal growth with heterogeneous nucleation are possible mechanisms for the crystallization process. Moreover, optical constants such as the optical band gap, refractive index, extinction coefficient, high-frequency dielectric constants, real and imaginary parts of dielectric constants were found to strongly depend on the annealing temperature. The optical energy gap decreased from 1.1 to 0.89 eV as the annealing temperature increased from 373 to 433K. These results indicate that thermal annealing is a major factor that can be used to tune the crystal structure, and hence the optical properties of As30Te67Ga3 system.

Dielectric relaxation and electrochemical studies on trihexyl tetradecyl phosphonium chloride [P14,6,6,6][Cl] ionic liquid

The conductivity relaxation, charge transport and electrochemical performance of trihexyl tetradecyl phosphonium chloride ([P14,6,6,6][Cl]) ionic liquid were studied by broadband dielectric spectroscopy and electrochemical workstation. Dielectric spectroscopy reviews polarity fluctuations due to the collective rotational dynamics of dipolar species and in electrically conductive systems an additional translational contribution due to charge transport was reported. The conductivity relaxation was fitted with Random barrier model by Dyre and secondary relaxation was fitted with Havriliak –Nigami function. The temperature dependence of the conductivity relaxation time can be described by Vogel – Fulcher – Tamman (VFT) equation. From the VFT fits the glass transition temperature was estimated as Tg=195.03K·The secondary relaxation was detected below the glass transition temperature and activation energy, Ea=15kJ/mol was estimated from the Arrhenius law. The electrochemical behaviour of [P14,6,6,6][Cl] was studied by fabricating an electrochemical supercapacitor and cyclic voltammetry, impedance spectroscopy and charge-discharge investigations were conducted to assess the performance of the supercapacitor. A very high specific capacitance of 370F/g with high rate scalability (up to 1000 cycles) and increased operation voltage of 3.5V were achieved to propose this electrolyte is a promising electrolyte for practical supercapacitor applications.

Effects of chemical composition and mean coordination number on glass transitions in Ge–Sb–Se glasses

Glass transitions in the Ge–Sb–Se glasses were investigated by means of differential scanning calorimetry (DSC) under non-isothermal conditions. The glass transition temperature [Formula: see text], activation energy of glass transition [Formula: see text], and fragility index as functions of the mean coordination number (MCN) and atomic percent of Ge were examined. The maximum value of [Formula: see text] in each group of the glasses occurred at the chemically stoichiometric composition, suggesting a glass transition threshold. The [Formula: see text] and fragility index were calculated from the heating rate dependence of [Formula: see text]. Both [Formula: see text] and fragility index show the minima at MCN = 2.4 which can be attributed to the structural phase transition of a covalently glassy network at MCN = 2.4. The analysis of the experimental results suggests that both the chemical composition and MCN have significant effects on the glass transitions in Ge–Sb–Se glasses.

Crystallization kinetics and phase transformation studies on glassy Se85In15-xSbx system

Our aim in the present research work is to investigate the crystallization kinetics and phase transformation studies in Se85In15-xSbx semiconductor. DSC measurements were done at constant heating rates of 5, 10, 15, 20 and 25 K/min for Se85In15-xSbx alloys. The glass transition (Tg), on-set crystallization (Tc) and peak crystallization (Tp) temperature were found to be increases with heating rate for all samples. The activation energy for glass transition (ΔEg) and crystallization (ΔEc) were calculated by different approaches and found to be nearly identical. Thin films of Se85In15-xSbx alloys were prepared by the thermal evaporation technique and the effect of thermal annealing on optical properties were discussed by means of optical absorption measurements. The optical band gaps were found to decrease with annealing temperature. This decrease in optical band gap can be associated with phase change in Se85In15-xSbx alloys from amorphous to crystalline phase.

Crystallization behavior of WO3-MoO3-TeO2 glasses

In the present study, crystallization behavior of tungsten molybdenum tellurite glasses was investigated by non-isothermal methods using differential scanning calorimetry (DSC), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) techniques. Thermal properties of glasses were investigated to calculate the values of glass transition temperature (Tg), crystallization temperature (Tc/Tp), temperature difference (ΔT), thermal stability (S), glass transition activation energy (Eg) and fragility parameter (m). Average cross-link density (nc¯) values were calculated for the physical investigation of the glasses. The crystallization kinetics was studied at different heating rates and the values of Avrami constant (n) and morphology index (m) were calculated from the Ozawa equation and the activation energy of crystallization (Ec) was determined using the modified Kissinger equation. The crystallized and/or transformed phases and their morphologies were determined by XRD and SEM analysis. Studied glass compositions were found to be thermally stable, resistant to crystallization and therefore suitable for opto-electronic applications.

Thermal analysis of cadmium addition on the glass transition and crystallization kinetics of Se–Te–Sn glassy network

Calorimetric measurements have been performed in quaternary glassy system Se78−xTe20Sn2Cdx (x = 0, 2, 4, and 6) to study the thermally induced glass transition and crystallization phenomena. The characteristics kinetic temperatures (glass transition temperature $$T_{\text{g}}$$ , onset crystallization temperature $$T_{\text{o}}$$ , peak crystallization temperature $$T_{\text{c}}$$ ) and static melting temperature $$T_{\text{m}}$$ of the quaternary glassy series have been determined using their non-isothermal DSC curves. These temperatures were utilized to calculate the thermal stability $$S$$ and the Hruby parameter $$H_{\text{R}}$$ for the studied glasses. Both the activation energy of glass transition $$E_{\text{t}}$$ and the activation energy of crystallization $$E_{\text{c}}$$ for all compositions were evaluated using the well-known Kissinger's relation and the method of Augis–Bennett. Values of the fragility index $$m$$ and the crystallization rate factor $$K_{\text{p}}$$ were estimated using the activation energy values $$E_{\text{t}}$$ and $$E_{\text{c}}$$ , respectively. The compositional dependence of the above-mentioned parameters was discussed on the basis of rigidity models and according to the formation of iono-covalent bonds when our glassy Se–Te–Sn system is doped with a heavy element as Cd.

Kinetics of glass transition of GeySe94-yIn6 (y = 10, 15 and 20) chalcogenide glasses under non-isothermal condition

ABSTRACTKinetics of glass transition of GeySe94-yIn6 (y = 10, 15 & 20) glassy alloys has been studied under non-isothermal condition using Differential Scanning Calorimetery (DSC). The glassy alloys have been prepared by rapid quenching of melt technique. For structure characterization, XRD and EDAX techniques have been used. DSC thermograms have been recorded at heating rates 5, 10, 15 and 20 K/min. from room temperature to 823 K. Lasocka's empirical relation has been used to study the heating rate dependence of glass transition temperature. Activation energy of glass transition, evaluated from Kissinger Peak shift method, increases with increase of Ge content in GeySe94-yIn6 (y = 10, 15 & 20) glassy series.

Physical and thermal characterization and glass stability criteria of amorphous silver-vanadate-tellurate system at different heating rates: Inducing critical Ag2O/V2O5 ratio

Transition metal oxide containing glasses (TMOGs) have unique thermal properties. This work gives an insight into the thermal stability and the compositional dependence of thermal properties for the understudied glasses. Also, physical, some optical and thermal characterization of 40TeO2-(60−x)V2O5-xAg2O glasses have been investigated in the compositional range of 0≤x≤50mol%. DSC experiments were performed on powder samples with a weight of 5mg, within the temperature range of 30–400°C at heating rates φ=2.5, 5, 7.5 and 10K/min, to obtain the glass transition temperature (Tg) and crystallization temperature (Tcr). The heating rate dependence of Tg has been used to study the applicability Kissinger formula describing the glass transition, in order to determine the glass transition activation energy (Ea). Ea values show that it ranged from 563.22kJ/mol to 268.36kJ/mol, indicating that (in relation/justification to other thermal and structural data) less fragility and so higher thermal stability is devoted to in the case of x=20mol%. The previously reported optical absorption spectra and optical band gap (Eg) by the same author were used to evaluate the refractive index (n),which both Eg and n have a behavior change at critical content of x=20mol%, implying to a drastic structural change with increasing Ag2O. Also, the physical parameters such as density (ρ), molar volume (Vm), oxygen molar volume (VO∗), oxygen packing density (OPD), molar refraction (Rm) and metallization criterion (M) have been evaluated and discussed, showing a behavior change at x=20mol%. Different glass stability parameters and different criteria of fragility have been checked, which show that glass with x=20 has the good stability among the present glasses. In brief, glass with x=20 has relatively high thermal stability, high glass forming tendency, higher OPD and VO∗, and so lower non-bridging oxygen ions (NBOs), which show that it is suitable option and promising material for optical and optoelectronic devices such as base semiconductor in solar cells and optical fibers because of its resistance against thermal attacks and also its narrower band gap.

Sub-Tg annealing effect on the kinetics of glass transition and crystallization for a Ti-Zr-Be-Fe bulk metallic glass

The influence of sub-Tg pre-annealing on the kinetics of glass transition and crystallization of a lightweight Ti41Zr25Be28Fe6 bulk metallic glass (BMG) has been investigated by isochronal and isothermal differential scanning calorimetry tests. It was found that sub-Tg annealing obviously enlarges the supercooled liquid region of Ti41Zr25Be28Fe6 BMG, indicating an enhanced thermal stability. The activation energies for glass transition and crystallization of the as-cast and pre-annealed samples have been calculated and compared. The pre-annealed samples possess smaller values of fragility parameter and longer incubation times upon isothermal heating compared with the as-cast sample, indicating a retarded crystallization process. The isothermal crystallization kinetics of the samples with different annealed states has been investigated in terms of the Johnson-Mehl-Avrami equation and local Avrami exponent. The current study reveals a clear sub-Tg annealing effect on the kinetics of glass transition and crystallization of Ti41Zr25Be28Fe6 glassy alloy and the possible mechanisms have also been proposed.

Glass transition kinetics aspects of amorphous Se60Ge15As25 and Se60Ge15Sn25 compositions

This work aims to research the glass transition kinetics aspects for Se60Ge15As25 and Se60Ge15Sn25 compositions, utilized differential thermal analysis technique under the non-isothermal condition at various heating rates. Glass transition temperature (T g) has been discovered heating rate and composition dependence. Composition reliance of T g can be comprehended with the correlation between T g and coordination number and mean bond energy also for the investigated compositions. Heating rate dependence of T g reveals the activation energy of glass transition (E g) values according to various methods for T g with various definitions. The estimated E g values have been discovered enlarging with temperature throughout the glass transition region. The relative error (e %) for Kissinger’s activation energy and its related parameters have been resolved and discussed. The correlation between glass transition and crystallization temperatures reveals that the crystallization process is more sensitive to heating rate than glass transition process. The critical heating rate value reflects that the Se60Ge15As25 composition is the most thermal stable composition. Fragility index values have been assessed by various relations and categorized the compositions under review as strong glasses.

On the crystallization kinetics of Zr–(Co,Ni)–Al bulk metallic glasses

Zr-based amorphous alloys are promising materials applied in engineering field, due to their strong glass-forming ability, outstanding mechanical properties and relatively low cost. In this work, the crystallization kinetics of Zr[Formula: see text]Co[Formula: see text]Ni[Formula: see text]Al[Formula: see text] ([Formula: see text], 2, 4 and 8; marked as Ni0, Ni2, Ni4 and Ni8, respectively) alloys are investigated in detail. The results show that, due to the addition of Ni, the glass transition of the alloys presents obvious dynamic characteristics, i.e., with the increasing heating rate, all characteristic temperatures are shifted to higher temperature. By fitting the Kissinger equation, the glass transition activation energy of Ni8 is the highest, indicating that Ni8 is much more difficult to crystallize. Therefore, the Ni8 alloy has the strongest anti-crystallization ability in the Zr[Formula: see text]Co[Formula: see text]Ni[Formula: see text]Al[Formula: see text] alloys investigated.

Non-isothermal crystallization kinetics of As30Te60Ga10 glass

The crystallization study under non-isothermal conditions of As30Te60Ga10 glass was investigated. The studied composition was synthesized by melt-quenching technique and characterized by different techniques such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The XRD analysis revealed that the as-prepared and annealed bulk glass of As30Te60Ga10 exhibit the amorphous, and polycrystalline nature, respectively. The DSC results showed that the heating rate affects the characteristic temperatures, for instance, the glass transition, onset, and peak crystallization temperatures. Furthermore, some thermal analysis methods such as the Kissinger and Matusita et al., approximations were employed to determine the crystallization parameters: for example Avrami exponent and the activation energies for glass transition and crystallization process. In addition, we have compared the experimental DSC data with the calculated ones based on the Johnson–Mehl–Avrami (JMA) and Sestak-Berggren SB(M,N) models. The results indicated that the SB(M,N) model is more suitable for describing the non-isothermal crystallization kinetics of the investigated composition.

Effect of lithium salt on physicochemical properties of P(MMA-co-EMA) based copolymer electrolytes for dye-sensitized solar cell application

In the present work, free standing films of methyl methacrylate and ethyl methacrylate complexed with different weight ratios of lithium iodide salt were successfully prepared via solution casting technique. Fourier transform infrared spectroscopy showed that the interaction between lithium ion and oxygen atoms occurred at carbonyl and ether group of the host copolymer. The incorporation of 20 wt% lithium iodide optimized the ambient temperature conductivity of the electrolyte up to 1.3 × 10−6 S cm−1. The glass transition temperature and activation energy decreased with increase in ionic conductivity which can be explained by the increase of segmental motion in polymer matrix resulting in enhancement of ion mobility. The majority of ions in this copolymer systems were anions as confirmed from lithium transference number measurements. The dye-sensitized solar cell fabricated using the highest conducting film exhibited photovoltaic response efficiency of 0.45%.

Kinetics based evidence for intermediate phase in Ge15Te85 − xInx chalcogenide glasses

This paper presents the thermal studies carried out using Differential Scanning Calorimetry on Ge15Te85−xInx glasses (1≤x≤11) to find glass transition temperature, Tg and crystallization temperature, Tx. Further, the variation of Tg and Tx for different heating rates have been studied. The composition dependence of Tx, Tg and stability factor, ΔT have been investigated. The crystallization kinetics has been studied by a non-isothermal method; the activation energy of crystallization, Ex has been determined using Kissinger method whereas glass transition activation energy, Eg using Kissinger as well as Tool-Narayanaswami-Moynihan (TNM) methods for all the compositions. The results obtained reveal the opening of an intermediate phase, IP in the composition range 2≤x≤7. Tg, Tx and ΔT increases continuously across the IP region. The Ex exhibits a plateau and Eg follow a bell shaped curve in the IP region.

Crystallization kinetics of Sn doped Ge20Te80−xSnx (0 ≤ x ≤ 4) chalcogenide glassy alloys

Chalcogenide semiconductors have evolved as multifunctional materials due to their fascinating thermal, optical, electrical and mechanical properties. In this report, Ge20Te80−xSnx (0 ≤ x ≤ 4) glassy alloys are systematically studied in order to understand the effect of variation of Sn content on the thermal parameters such as glass transition (Tg), onset crystallization (Tc), peak crystallization (Tp), melting temperature (Tm), activation energy of glass transition (Eg), and crystallization (Ec). The values of Eg are calculated from the variation of Tg with the heating rate (α), according to Kissinger and Moynihan model, while the values of Ec are calculated from the variation of Tp with the heating rate (α), according to Kissinger, Takhor, Augis-Bennett and Ozawa model. Thermal stability and glass forming ability (GFA) are discussed for understanding the applicability of the synthesized materials in phase change memory (PCM) applications. Thermal parameters are correlated with the electrical switching studies to get an insight into the phase change mechanism. The results of the calculated thermal parameters reveal that the GFA of the synthesized Ge20Te80−xSnx (0 ≤ x ≤ 4) glassy alloys has a synchronous relationship with their thermal properties studied through differential scanning calorimetry, indicating their potential for phase-change memory device applications.

STUDY THE THERMAL AND ELECTRICAL PROPERTIES OF SOME MAGNESIUM-BORO-PHOSPHATE GLASSES CONTAINING VANADIUM OXIDE.

Glasses having the molecular composition 20 MgO - 30 B2O3 - (50-x) P2O5 – x V2O5 –- (x = 0, 5, 10, 15 and 20 mol %) have been prepared by the conventional melt quenching method. The thermal and electrical transport properties of the prepared glasses were thoroughly investigated by using differential thermal analysis technique and LCR meter-bridge with four fixed frequencies. All the obtained thermal parameters are found to depend on the composition and heating rate. Both the activation energy of glass transition and activation energy of crystallization as well as the thermal stability are found to increase with the gradual increase of vanadium oxide content. It was found that, all samples exhibit semi-conduction properties and the conduction mechanism was found to be the small polaron hoping at relatively low temperatures while at relatively higher temperatures, the correlated barrier hoping model was found to be dominant. Also, as vanadium oxide was gradually increased, the conductivity, dielectric constant and dielectric loss factor exhibit gradual increase.

Crystallization kinetics of tellurium-rich Se–Te–Sn glassy alloys

Differential scanning calorimetry (DSC) has been used to study the non-isothermal crystallization kinetics of Se30Te70−xSnx (for x = 0, 1.5 2.5 and 4.5) glassy alloys. Characteristic kinetic parameters say glass transition temperature (T g), peak crystallization temperature (T p) and melting temperature (T m) are determined from the DSC curves, recorded at four different heating rates, i.e., 9, 12, 15, 18 K min−1. The characteristic temperatures T g, T c and T m are found to increase with an increase in Sn concentration as well as with the heating rate (α). The increase in T g, T p and T m may be ascribed to the increase in cross-linking of amorphous network due to the dispersion of Sn into the Se chains. The activation energy of glass transition (E g), crystallization activation energy (E c) and Avrami exponent (n) have been evaluated from the heating rate dependence of T g, T c and T p using Kissinger, Mahadevan, Augis-Bennett and Moynihan methods. Thermal stability and glass-forming ability of amorphous Se30Te70−xSnx alloy have also been examined. Our results show that Se30Te70−xSnx composition, with thermal stability parameter H R > 0.5, is thermally stable and has characteristics of good glass former. Further, the composition corresponding to x = 1.5 is found to be thermally more stable as compared to the other compositions.

Calorimetric study of Sb-modified Ge–Se–Te glassy alloys

The glassy compositions of Ge 16 Se 52 Te 32−x Sb x system, obtained using rapid melt quenching technique, have been characterized by calorimetric study at different heating rates in this study. A systematic investigation of the crystallization kinetics is carried out for these compositions. Composition corresponding to atomic % 8 of Sb has good thermal stability. The material exhibits the unique thermal properties, which makes it suitable to use for electrical or memory switching devices. Various thermal parameters, activation energies of glass transition and crystallization are calculated using relevant approaches.

Study on glass transition temperature and kinetics of Cu–Zr glassy alloys

Ideal glass transition temperatures and transition activation energies of Cu46Zr45Al9 metallic glass was investigated using differential scanning calorimetry (DSC). The Vogel–Fulcher–Tammann temperature T 0 and Kauzmann temperature T k were determined, respectively, and T 0 is greater than T k. Meanwhile, activation energies of glass transition E g, onset crystallization E x and crystallization peak E p were deduced to be 634.2 ± 15, 444 ± 16.1 and 366.8 ± 25.1 kJ mol−1, which indicates that glass transition is harder than crystallization process to proceed.

Kinetic characterization of TeO2–Bi2O3 –V2O5 –Na2O –TiO2 glass system

In continuation of our earlier work on (the mechanical and thermal properties of TeO2–Bi2O3 –V2O5 – Na2O–TiO2 glass system), in this study, we have investigated the kinetic parameters of this system as a function of increasing TiO2 mol% by using differential scanning calorimetry (DSC) data under non-isothermal (isochronal) conditions. The thermodynamic fragility (F) and the glass forming tendency (Kg), (TgTm) factors of the present glass have been evaluated to determine the relationship between the change in the structure and the thermal stability of the glass. The activation energies of both glass transition (Eg) and crystallization (Ec) processes have been evaluated by the methods of Kissinger and Ozawa by the data obtained from (DSC) at heating rates (β) 10, 15, 20 and 25K/min. The quantitative interpretation of these kinetic parameters has been carried out by coupling with the previous estimated elastic moduli. The kinetic Avrami coefficient (n) was also calculated by several estimation methods to determine and confirm the mechanism of the crystallization process.