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The performance of in situ Raman microscopy (IRM) in monitoring the crystallization kinetics of amorphous drugs (griseofulvin and indomethacin) was evaluated using a comparison with the data obtained via differential scanning calorimetry (DSC). IRM was found to accurately and sensitively detect the initial stages of the crystal growth processes, including the rapid glass–crystal surface growth or recrystallization between polymorphic phases, with the reliable localized identification of the particular polymorphs being the main advantage of IRM over DSC. However, from the quantitative point of view, the reproducibility of the IRM measurements was found to be potentially significantly hindered due to inaccurate temperature recording and calibration, variability in the Raman spectra corresponding to the fully amorphous and crystalline phases, and an overly limited number of spectra possible to collect during acceptable experimental timescales because of the applied heating rates. Since theoretical simulations showed that, from the kinetics point of view, the constant density of collected data points per kinetic effect results in the smallest distortions, only the employment of the fast Raman mapping functions could advance the performance of IRM above that of calorimetric measurements. [ABSTRACT FROM AUTHOR]

The processes of structural relaxation, crystal growth, and thermal decomposition were studied for amorphous griseofulvin (GSF) by means of thermo-analytical, microscopic, spectroscopic, and diffraction techniques. The activation energy of ~395 kJ·mol−1 can be attributed to the structural relaxation motions described in terms of the Tool–Narayanaswamy–Moynihan model. Whereas the bulk amorphous GSF is very stable, the presence of mechanical defects and micro-cracks results in partial crystallization initiated by the transition from the glassy to the under-cooled liquid state (at ~80 °C). A key aspect of this crystal growth mode is the presence of a sufficiently nucleated vicinity of the disrupted amorphous phase; the crystal growth itself is a rate-determining step. The main macroscopic (calorimetrically observed) crystallization process occurs in amorphous GSF at 115–135 °C. In both cases, the common polymorph I is dominantly formed. Whereas the macroscopic crystallization of coarse GSF powder exhibits similar activation energy (~235 kJ·mol−1) as that of microscopically observed growth in bulk material, the activation energy of the fine GSF powder macroscopic crystallization gradually changes (as temperature and/or heating rate increase) from the activation energy of microscopic surface growth (~105 kJ·mol−1) to that observed for the growth in bulk GSF. The macroscopic crystal growth kinetics can be accurately described in terms of the complex mechanism, utilizing two independent autocatalytic Šesták–Berggren processes. Thermal decomposition of GSF proceeds identically in N2 and in air atmospheres with the activation energy of ~105 kJ·mol−1. The coincidence of the GSF melting temperature and the onset of decomposition (both at 200 °C) indicates that evaporation may initiate or compete with the decomposition process. [ABSTRACT FROM AUTHOR]

Non-isothermal differential scanning calorimetry (DSC) was used to study the influences of particle size (daver) and heating rate (q+) on the structural relaxation, crystal growth and decomposition kinetics of amorphous indomethacin. The structural relaxation and decomposition processes exhibited daver-independent kinetics, with the q+ dependences based on the apparent activation energies of 342 and 106 kJ·mol−1, respectively. The DSC-measured crystal growth kinetics played a dominant role in the nucleation throughout the total macroscopic amorphous-to-crystalline transformation: the change from the zero-order to the autocatalytic mechanism with increasing q+, the significant alteration of kinetics, with the storage below the glass transition temperature, and the accelerated crystallization due to mechanically induced defects. Whereas slow q+ led to the formation of the thermodynamically stable γ polymorph, fast q+ produced a significant amount of the metastable α polymorph. Mutual correlations between the macroscopic and microscopic crystal growth processes, and between the viscous flow and structural relaxation motions, were discussed based on the values of the corresponding activation energies. Notably, this approach helped us to distinguish between particular crystal growth modes in the case of the powdered indomethacin materials. Ediger's decoupling parameter was used to quantify the relationship between the viscosity and crystal growth. The link between the cooperativity of structural domains, parameters of the Tool-Narayanaswamy-Moynihan relaxation model and microscopic crystal growth was proposed. [ABSTRACT FROM AUTHOR]

Amorphous Sb 2 Se 3 thin films (200–1500 nm) deposited on Kapton foil were crystallized in controlled environment using the method of direct calorimetric measurement of thin films. X-ray diffraction was used to determine the intensity of the 1D (Sb 4 Sb 6) n ribbons preferential orientation in dependence on the processing conditions: film thickness, energy flux during the pulsed laser deposition (PLD), heating rate, low and high temperature annealing. Lower PLD energy flux combined with higher deposited film thickness (1500 nm) led to increased orientation in the [2 2 1] direction, which is favorable for thin film solar cells application. Raman spectroscopy showed that thermally induced crystallization produces oxide-free Sb 2 Se 3 thin films. Description of the crystallization kinetics led to very accurate kinetic predictions for the isothermal annealing conditions suitable for preparation of glass-ceramics with defined amount of crystalline phase – the predictions were accurate to ∼10% of the true (experimentally determined) value. [ABSTRACT FROM AUTHOR]

Non-isothermal differential scanning calorimetry (DSC) was used to study the influences of particle size d aver and heating rate q+ on the crystal growth and decomposition kinetics of amorphous N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)-benzidine (TPD). The macroscopic crystallization kinetics was found to be strongly dependent on q+. At high q+, the crystal growth proceeded dominantly from the mechanical defects acting as primary growth centers, with the corresponding activation energy being ∼70–80 kJ mol−1. At low q+, the crystalline phase was primarily formed from heterogeneous nuclei, with the activation energy for the growth process being ∼980 kJ mol−1. The prolonged nucleation led to extensive passivation of the surface mechanical defects with respect to their function as direct crystal-growth-accelerating centers. Temperature-resolved in-situ Raman microscopy has confirmed the conclusions derived from the DSC data and helped to identify the residual low-q+ defects-originating crystal growth as proceeding from volume-located micro-cracks. The X-ray diffraction analysis confirmed that TPD crystallizes into an identical phase under all circumstances. The thermal decomposition of TPD was found to proceed in a single step, by simple nth-order reaction kinetics with the activation energy of ∼120 kJ mol−1. [Display omitted] • Crystal growth and thermal decomposition of TPD were studied by means of DSC. • Crystallization rate and thermal stability are strongly dependent on heating rate. • Prolonged nucleation leads to extensive passivation of surface mechanical defects. • Thermal decomposition of TPD proceeds with nth-order reaction kinetics. [ABSTRACT FROM AUTHOR]

The self-plasticization, i.e., the increase in the polymer segmental mobility by the inclusion of its own monomer, has a major impact on the structural, thermal, and mechanical properties of the polymer. Differential scanning calorimetry (DSC) was used to investigate the influence of thermally induced self-plasticization on the structural relaxation of polydioxanone (PDX). Depolymerization (based dominantly on the end-chain scission mechanism) was found to be controlled by the depolymerization temperature T d as well as the actual number of re-melting cycles (while keeping the time spent at T d constant). PDX samples with the glass transition temperature (T g) ranging from −52 (highly plasticized) to −13 °C (virgin) were prepared. The DSC data were described in terms of the Tool-Narayanaswamy model; a consistent structural relaxation behavior associating the degree of plasticization with T g was identified. The activation energy first decreased with plasticization from 430 kJ mol−1 to 210 kJ mol−1 in the T g range of −40 to −13C, which is consistent with the plasticization-caused spacing-apart of the polymer chains resulting in larger free volume and increased freedom for the relaxation movements. For the highly plasticized PDX samples, the activation energy increased from 210 kJ mol−1 to 310 kJ mol−1, which appears to be associated with the possible segregation of the portion of the plasticizer into a discrete phase. The width of the relaxation times distribution increased with plasticization as a consequence of the plasticizer loosening the polymeric chains and enabling a wider variety of the segmental movement. The plasticization also leads to a higher dependence of the segmental relaxation movements on their current physico-chemical and steric surrounding. [Display omitted] • Thermal depolymerization-based plasticization of polydioxanone was studied by DSC. • Glass transition kinetics was described in terms of TNM model. • Self-plasticization decreases activation energy of structural relaxation. • The width of the relaxation times distribution increased with plasticization. • Plasticization led to more intense interaction of the polymer chains. [ABSTRACT FROM AUTHOR]

Abstract Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used in conjunction to study thermokinetic behavior of (GeTe 4) y (GaTe 3) 100-y bulk infrared glasses (for y between 40 and 100). The DSC data were utilized to describe the glass transition and crystallization kinetics in terms of the Tool-Narayanaswamy-Moynihan and Šesták-Berggren models, respectively. The kinetic data are of sufficient quality to enable predictions utilizable for preparation of Ge-Ga-Te ceramics and glass-ceramics. Whereas the compositional evolution of the positions of glass transition and crystallization effects was found to be small, the activation energies obtained for the two processes have shown that in case of the crystallization process the applied heating rate q+ has large influence on the position of the corresponding kinetic peak on the temperature axis (T c) and, consequently, on the values of glass stability and glass-forming criteria calculated by using this value. For this reason, a new viscous-flow-related criterion, which utilizes the joint DSC and TMA measurements and is independent from applied q+, was derived to consider the thermal stability of the glassy materials with regard to their processing (fiber-drawing or shape-molding). Based on the newly developed criteria, the (GeTe 4) 67 (GaTe 3) 33 glass (positioned near the eutectic) was found to be optimal with respect to the fiber-drawing procedure. Highlights • Thermal behavior of (GeTe 4) x (GaTe 3) 100-x bulk glasses was studied by DSC and TMA. • Glass transition kinetics was described by the Tool-Narayanaswamy-Moynihan formalism. • Crystallization kinetics was described in terms of the AC model. • Correlation of DSC and TMA data determined true workability window for fiber-drawing. • New viscous-flow-related criterion determining true thermal stability was derived. [ABSTRACT FROM AUTHOR]

Abstract Influence of oxygen atmosphere on crystallization of (GeSe 2) x (Sb 2 Se 3) 1-x glasses (for x = 0.3, 0.4 and 0.5) was investigated by differential scanning calorimetry, X-ray diffraction analysis and infrared microscopy. Particle-size-dependent study was performed to reveal the role of mechanically induced defects. The presence of oxygen led to an early formation of a thin surface crystalline layer (smoothly structured) that significantly influenced further crystal growth. The most pronounced consequence was surprisingly found in case of the (GeSe 2) 0.3 (Sb 2 Se 3) 0.7 composition that crystallizes in volume. The thin surface crystalline layer hindered the macroscopic viscous flow, so that the samples retained their original shape, and these quasi-stationary conditions accelerated the initial nucleation and growth rates. At the same time, however, these conditions prevented the samples from reaching full crystallinity. In case of the compositions with x = 0.4 and 0.5, the crystal growth proceeded only at the surface and presence of external interfaces and mechanically induced defects took over the major role driving the crystallization kinetics. Correlation of the calorimetric, microscopic and viscosity data is discussed in detail. Highlights • Influence of reaction atmosphere on crystallization of (GeSe 2) x (Sb 2 Se 3) 1-x glasses was studied. • Presence of oxygen accelerates surface crystal growth • Kinetic description of crystallization process was done in terms of AC model. • External interface and mechanically induced defects largely affect the crystallization rate. [ABSTRACT FROM AUTHOR]

Abstract Differential scanning calorimetry, infrared microscopy and X-ray diffraction analysis and were used to investigate the influence of reaction atmosphere (air versus pure nitrogen) on crystallization behavior of (GeSe 2) 0.3 (Sb 2 Se 3) 0.7 glass. The presence of oxygen was found to accelerate the crystal growth both on surface and in bulk material, with a similar effect in case of powders and bulk samples. Detailed crystallization kinetics study was performed, revealing that the presence of oxygen leads to a lowered activation energy and steeper onset of the process – single-curve-averaged masterplot approach was used to deal with the temperature-differentiated complexity of the crystallization. Direct observations by infrared microscopy have shown that the presence of oxygen leads to a formation of robust surface crystalline layer, which prevents powder sintering and bulk samples deformation by viscous flow, and to a more rapid nucleation and crystal growth within the sample volume. Based on the viscosity values estimated for the crystallization temperatures, an explanation for the accelerated volume crystallization was proposed, employing the quasi-stationary conditions contributing to better cohesivity of critical nuclei and crystal/glass interface. The existence of the surface crystalline layer however prevents the sample from reaching full crystallinity. Highlights • Influence of reaction atmosphere on crystallization of (GeSe 2) 0.3 (Sb 2 Se 3) 0.7 glass was studied. • Presence of oxygen accelerates crystal growth on surface as well as in bulk material. • Formal kinetic description of crystallization process was performed. • Presence of oxygen partially inhibits powder sintering above glass transition. [ABSTRACT FROM AUTHOR]

Abstract Combined calorimetric and structural study, employing the techniques of differential scanning calorimetry and Raman spectroscopy, was performed to describe the enthalpy relaxation processes in the (GeSe 2) y (Sb 2 Se 3) 1-y chalcogenide glasses. The full glass forming compositional region (y = 0.3–0.9) was explored. The enthalpy relaxation was described in terms of the phenomenological Tool-Narayanaswamy-Moynihan model. Compositional evolution of the glass transition temperatures and relaxation activation energies was explained based on the changing average bond energies and overall interconnectivity of the glassy matrices. Resemblance between the activation energies of the relaxation processes and viscous flow was confirmed for all studied glasses. Non-linearity and non-exponentiality of the enthalpy relaxation were found to be invariant with composition. The structural relaxation kinetics as well as kinetic fragilities determined for the present (GeSe 2) y (Sb 2 Se 3) 1-y glassy system were very similar to the results obtained earlier for the (GeS 2) y (Sb 2 S 3) 1-y glasses, which can be attributed to the similarly constrained topology of the pseudo-binary compositional lines. [ABSTRACT FROM AUTHOR]

Abstract Differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared microscopy and Raman spectroscopy were used to study the crystallization behavior of the (GeTe 4) x (GaTe 3) 100-x glasses for far-infrared optics. Two independent overlapping crystallization processes were found – the initial surface-located precipitation of hexagonal Te and Ga 2 Te 5 phases, followed by formation of the rhombohedral GeTe phase. The initial precipitation process, and in particular the formation of the Ga 2 Te 5 phase, was found to be catalyzed by presence of mechanically induced defects. Finely powdered materials with higher GaTe 3 content also exhibited more pronounced separation of the two crystallization sub-processes. Glass stability of the prepared glasses was evaluated in terms of the Hrubý criterion - the (GeTe 4) 86 (GaTe 3) 14 composition was found to be the most stable and most resilient to the negative crystallization-enhancing influence of structure defects. Pros and cons of the compositional evolution of the crystallization behavior (determined via full kinetic description of the involved crystallization sub-processes and kinetic prediction of the crystallization behavior) were discussed with regard to the ceramics and glass-ceramics applications. Glasses with low GaTe 3 content appear to be most suitable for preparation of fully ceramic materials, whereas glasses with high GaTe 3 content seem to be most suitable for the glass-ceramics applications. Highlights • Thermal behavior of (GeTe 4) x (GaTe 3) 100-x glasses was studied by DSC and XRD. • Crystallization process was studied non-isothermally in dependence on particle size. • Crystallization kinetics was described in terms of the Johnson-Mehl-Avrami and AC models. • Suitability towards preparation of ceramics and glass-ceramics is discussed. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry was used to study thermokinetic behavior of (As2Se3)100−x(As2Te3)x infrared glasses (seven compositions along the pseudo‐binary were investigated). Glass‐transition kinetics was described in terms of the Tool‐Narayanaswamy‐Moynihan model and the relaxation motions were interpreted using Raman spectroscopy data. The enthalpy relaxation kinetics was found to be absolutely uninfluenced by changing Se/Te ratio. On the other hand, DSC crystallization behavior changed significantly with increasing As2Te3 content: Te‐rich compositions show marked affinity toward crystallization, whereas in case of the compositions with 0‐34 mol.% As2Te3 crystal growth is significantly suppressed. X‐ray diffraction analysis indicated presence of monoclinic As2Se3, As2Te3, and As2Se(Te)3 phases. The complex crystallization behavior occurring in case of the Te‐rich compositions was described by superposition of two autocatalytic kinetic signals. Based on the information from infrared microscopy the two overlapping crystallization processes can be attributed to the respective formations of spherulitic and needle‐shaped crystallites. Best glass stability was identified in case of the (As2Se3)66(As2Te3)34 composition, which appears to be a potential candidate for optic applications in the far‐infrared region of the spectrum. [ABSTRACT FROM AUTHOR]

Thermo-kinetic behavior of Ce-doped 45S5 bioactive glass (addition of CeO 2 up to 1.5 mol.%) was explored by means of calorimetry and thermomechanical analysis. The apparent activation energy of structural relaxation was estimated to vary in the 540–670 kJ mol−1 range. The relaxation process exhibited broad distribution of relaxation times and the relaxation motions were found to only weakly depend on the material's structure. The activation energy of viscous flow was found to vary in the 585–615 kJ mol−1 range; the viscosity itself showed Arrhenian behavior within 107–1011 Pa s. Thermal stability of the glasses was found to be non-monotonous and generally very low, with the most stable glass composition being 45S5 + 0.5 mol.% CeO 2. The cold crystallization was found to behave autocatalytically, with the activation energy decreasing from 360 to 310 kJ mol−1 with the gradual addition of CeO 2. While the bulk glasses were crystallization-resistant up to 620 °C, the powdered material with CeO 2 content ≥1 mol.% was predicted to crystallize even at temperatures slightly above the glass transition temperature. [ABSTRACT FROM AUTHOR]

Recrystallization kinetics of amorphous Enzalutamide (two batches prepared by hot-melt extrusion and thermal evaporation of the solvent) was studied by differential scanning calorimetry. The preparation route was found to have significant effect on material thermal stability and initial degree of crystallinity – solvent evaporation led to formation of partially crystalline matrix with residual solvent content causing plasticization and the ongoing thermally induced crystallization was largely accelerated. Thermal recrystallization of both Enzalutamide batches led to a similar polymorphic form. The recrystallization kinetics was evaluated by means of modified multivariate kinetic analysis and described in terms of the autocatalytic Šesták-Berggren and the nth order autocatalytic reaction models. The recrystallization kinetics were found to be dependent on applied heating rate, gradually shifting from the nucleation-growth kinetics to the autocatalyzed 0th order kinetics (with the effective order of reaction changing from 1 to 0.2). The autocatalytic Šesták-Berggren model appears to be more suitable for predictions of the Enzalutamide recrystallization behavior due to the constancy of the autocatalytic term (M = 0.55) with regard to the experimental conditions. In addition, the kinetic predictions of crystallization in pharmaceuticals were discussed in general based on theoretical simulations – importance of the aspects influencing the kinetic predictions was demonstrated. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry was used to study enthalpy relaxation kinetics of the (GeS 2 ) y (Sb 2 S 3 ) 1 − y glasses in the y = 0.1–0.9 compositional range. The relaxation behavior was described in terms of the phenomenological Tool-Narayanaswamy-Moynihan (TNM) model. Non-linear optimization procedure was used to determine unique set of relaxation parameters for each studied glass. With increasing GeS 2 content the activation energy of enthalpy relaxation was found to steeply decrease whereas the glass transition temperature increased significantly. Both non-linearity and non-exponentiality features were not affected by compositional changes. Raman spectra have shown that the Ge-S structural units, as opposed to the Sb-S units, are significantly interconnected and create a 3-dimensional network capable of solely carrying the relaxation motions, which is in agreement with the interpretation of compositional evolution of relaxation parameters. Moreover, based on the present data the controversy regarding the (GeS 2 ) y (Sb 2 S 3 ) 1 − y fragilities found in literature was clarified, and the free-volume concept employing the Avrami growth theory was disputed. [ABSTRACT FROM AUTHOR]

The structural relaxation and crystallization kinetics of the (As 2 Se 3 ) 0.5 (As 2 Te 3 ) 0.5 chalcogenide glass was studied by means of differential scanning calorimetry (DSC) and the influence of experimental conditions (particle size, heating rate) was observed. The Tool-Narayanaswamy-Moynihan (TNM) model was used for description of structural relaxation data. The structure of the studied glass was found to be similar to its purely selenide analogue (As 2 Se 3 ), but the Te atoms appear to randomly incorporate into the short Se-As-Te chains; also they coexist in AsTe 3/2 pyramidal units alongside the AsSe 3/2 units. In case of the description of the crystallization kinetics, the nucleation-growth Johnson-Mehl-Avrami (JMA) model and the semi-empirical autocatalytic AC(M,N) model were tested on experimental DSC data. The suitability of JMA model was not confirmed due to the complexity of crystallization, therefore the AC(M,N) model was applied. These results were supported by the structural information from XRD analysis, Raman spectroscopy and infrared (IR) microscopy. The presence of As-Te, As-Se and As 2 Se(Te) 3 phases was confirmed and the occurrence of tellurium in the structure has a huge influence on overall structure and subsequent thermal behavior of the (As 2 Se 3 ) 0.5 (As 2 Te 3 ) 0.5 glassy material. [ABSTRACT FROM AUTHOR]

Polydioxanone is used in numerous medical applications, e.g., biodegradable sutures and implants, for its excellent biocompatibility and appropriate degradation time. However, detailed knowledge of the polydioxanone thermokinetic behavior is essential to achieve the required properties of the particular medical appliance produced. Differential scanning calorimetry (DSC) was used for thermokinetic characterization of polydioxanone. The study was focused on three phenomena associated with the amorphous/semi-crystalline state: structural relaxation, cold crystallization, and thermal degradation. The glass transition kinetics was described in terms of the Tool-Narayanaswamy-Moynihan model with the following parameters: Δh* = 679 kJ mol−1, log(A/s) = −311.76, β = 0.50, x = 0.45. The increasing degree of crystalline phase in the polymeric matrix led for the relaxation movements to a gradually decreasing dependence on structural arrangement. The cold crystallization of polydioxanone was described in terms of the autocatalytic Šesták-Berggren model with the following parameters: E = 95.2 kJ mol−1, log(A/s−1) = 15.04, M AC = 0.79, N AC = 0.70. The highest achieved amounts of crystalline phase differed between 53 and 63% depending on the route to the crystal formation (either the crystal growth from the melt during slow cooling or the growth from the fully amorphous phase during slow heating). The kinetic predictions based on the non-isothermal and isothermal crystallization data were found to be in good agreement. Thermal decomposition of polydioxanone starts at 190 °C via depolymerization to p -dioxanone monomer and consequent evaporation. However, the polydioxanone starts to partially depolymerize already at 150 °C, shortening its chains and decreasing average molecular weight. Based on the present thermokinetic characterization, the optimum processing conditions for polydioxanone production by means of hot melt extrusion and molding were discussed. [Display omitted] • Thermokinetic characterization of polydioxanone was performed using DSC. • Glass transition kinetics was described in terms of TNM model. • Highest achieved degree of crystalline phase was 63 %. • PDX degrades via depolymerization and consequent evaporation. • PDX slowly depolymerizes already at 150 °C via unzipping mechanism. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study thermokinetic behavior of Ge 21 Se y Te 79−y infrared glasses (for y up to 8 at.% of Se). Glass transition kinetics was described in terms of the Tool-Narayanaswamy-Moynihan model and the relaxation motions were interpreted using Raman spectroscopy data. Both enthalpy and volume relaxation kinetics were found to be uninfluenced by Se addition. On the other hand, DSC crystallization behavior changed significantly with increasing Se content: initial addition of Se partially delays and decelerates both the initial Te precipitation and the consequent volume-located crystallization of GeTe and Te; additional increase of Se content then further delays and separates the volume-located crystallization processes but the initial surface Te precipitation is no longer affected. From this point of view the fine compositional tuning of basic thermal stability of Ge Te Se infrared glasses appears meaningless. On the contrary, glass workability window (determined by means of the TMA crystallization experiments) was found to be significantly affected by Se addition, emphasizing the importance of this type of measurements for the glass technology and material science. The 4 at.% Se content was found optimal with respect to fiber-drawing procedure. [ABSTRACT FROM AUTHOR]

Influence of oxygen presence on the crystallization behavior of (GeS 2 ) y (Sb 2 S 3 ) 1-y glasses (for y up to 0.3) was studied by differential scanning calorimetry, X-ray diffraction analysis and infrared microscopy - the study was performed in dependence on particle size. The oxygen was found to significantly accelerate crystallization from mechanically induced defects for the (GeS 2 ) 0.1 (Sb 2 S 3 ) 0.9 composition and to sustain the intensity of crystal formation in case of the (GeS 2 ) 0.2 (Sb 2 S 3 ) 0.8 and (GeS 2 ) 0.3 (Sb 2 S 3 ) 0.7 compositions. On the other hand, presence of oxygen influenced neither the morphology of the crystallites, nor the actual crystallization model-free and model-based kinetics. Direct microscopic observation confirmed strict surface crystallization for all studied composition. Compositional evolutions of the viscosity data and microscopically determined crystal growth rate curves have shown that it is the exceptionally high crystal growth rate and crystallization tendency (compared to the minor-to-moderate contribution of viscosity itself) that are responsible for the significant influenceability of the (GeS 2 ) 0.1 (Sb 2 S 3 ) 0.9 crystallization by the presence of oxygen. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry, X-ray diffraction analysis and infrared microscopy were used to investigate the influence of reaction atmosphere (air versus pure nitrogen) on crystallization behavior of (GeS 2 ) 0.1 (Sb 2 S 3 ) 0.9 powdered and bulk glass. The presence of oxygen was found to accelerate (in comparison to pure N 2 ) the crystallization process in dependence on particle size of the powdered glass. Large amounts of mechanically induced defects (and not the increased surface area) were found to be the key catalyzing factor. Formal kinetic description of the crystallization mechanism (presented in terms of the nucleation-growth model) remained unchanged by the presence of oxygen. In addition, also the crystallographic nature of the crystalline products was similar for crystallization in air and in pure N 2 . Direct observations by infrared microscopy confirmed that the (GeS 2 ) 0.1 (Sb 2 S 3 ) 0.9 glass crystallizes from surface. These observations also evidenced similar morphology of the crystallites growing in and without presence of oxygen, as well as the more preferential defects-based growth in case of the oxygenated samples. In addition, presence of oxygen was found to partially inhibit the powder sintering above the glass transition temperature. [ABSTRACT FROM AUTHOR]

The effect of Ag-doping on the thermokinetic behavior (cold crystallization and structural relaxation kinetics, glass-forming ability) of the Ag y [(GeS 2 ) 50 (Sb 2 S 3 ) 50 ] (100 − y) glasses was studied by using differential scanning calorimetry, Raman spectroscopy and X-ray analysis – compositions up to y = 25 were included in the study. Structural relaxation kinetics was found to be only very weakly influenced by the Ag-doping; the following Tool-Narayanaswamy-Moynihan parameters were determined (within a 10% variation) for the majority of the glasses: activation energy 400 kJ mol − 1 , non-linearity parameter 0.72, non-exponentiality parameter 0.85. On the other hand, the glass transition temperature decreased significantly with increasing Ag content – the effect can be explained by dilution of the original glassy matrix. Combination of these findings with the corresponding Raman spectra has shown that it is the Ge-S structural units that carry the main portion of the relaxation motions. Regarding the crystallization behavior, the Ag-doping led to decreased glass-forming ability and increased tendency of the glasses towards crystallization. The Ag-rich compositions exhibited during heating well-developed crystallization peaks driven by the autocatalytic Šesták-Berggren kinetics. The X-ray analysis has shown that in case of the Ag-rich compositions Sb and argyrodite crystallites tend to form during the melt-quench. [ABSTRACT FROM AUTHOR]

The influence of long-term laboratory-temperature degradation on the crystallization kinetics of the Se 90 Te 10 , Se 80 Te 20 and Se 70 Te 30 chalcogenide glasses was studied by differential scanning calorimetry. Periodical measurements during the 6 months aging period have shown that the fine Se-Te powders degraded largely, large degree of crystallinity occurred even though the materials were stored well below their glass transition temperature. The degradation increased with Te content. The defects-based residual crystallization kinetics exhibited by the fine Se-Te powders was not influenced significantly by the continuous degradation. Coarse Se-Te powders, on the other hand, exhibited only weak degradation with low amount of crystallinity occurring during the 6 months period but the crystallization kinetics of the degraded glasses changed markedly. The degraded coarse Se-Te powders have shown increased nuclei-based volume-located growth of crystallites, which indicates that nucleation proceeded significantly below the glass transition; the effect increased largely with Te content. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry was used to study enthalpy relaxation kinetics of the (GeTe 4 ) y (GaTe 3 ) 1 − y infrared chalcogenide glasses for the compositional range y = 0.4 − 1.0. The relaxation behavior was described in terms of the Tool-Narayanaswamy-Moynihan (TNM) model. Direct curve-fitting procedure was used to determine the values of TNM parameters; these results were successfully correlated with data provided by the non-fitting methodology based on the evaluation from constant-ratio (CR) cycles. The addition of GaTe 3 into the GeTe 4 matrix led to a moderate decrease of activation energy of the relaxation process and to a large increase of the relaxation linearity – the structural relaxation became driven solely by temperature. Interpretation of the compositional evolution of the TNM parameters was used to verify structural information provided by Raman spectroscopy and molecular dynamics simulations: the initial GaTe 3 addition causes dilution of the GeTe 4 tetrahedral network, which carries the main portion of the relaxation motions; further increase of GaTe 3 content then leads to an increase of connectivity outside the GeTe 4 sub-networks due to the threefold coordinated Ga atoms bonding with the lone-pair electrons of Te dimers and short chains. [ABSTRACT FROM AUTHOR]

The effect of long-term room-temperature degradation (up to 6 months) on Se 70 Te 30 crystallization kinetics was investigated by differential scanning calorimetry in dependence on experimental conditions of the measurement—applied heating rate and particle size of the powdered material. In case of very fine powders massive amorphous-to-crystalline degradation occurred even at room temperature, indicating that the small powder grains have fully defects-imbued inner structure that accelerates crystal growth. The kinetic data obtained for the consequent crystallization of the remaining glassy matrix showed that the defects-based Johnson-Mehl-Avrami crystallization is under quasi-equilibrium conditions further accelerated towards autocatalytic mechanism. Coarse powders, on the other hand, exhibited primary degradation only in a surface layer of the powder grains. The main effect of the coarse powders aging was found to be associated with marked enhancement of crystal growth originating from volume-located nuclei—either a sub-T g nucleation occurred during aging or some pre-existing nuclei were activated during this time (possibly via mechanical stresses arising from structural relaxation processes). [ABSTRACT FROM AUTHOR]

Cold crystallization and structural relaxation kinetic processes occurring in the Ge 11 Ga 11 Te 78 infrared bulk glass were studied using differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The complex crystallization behaviour was described as overlapping surface nucleation-growth Te precipitation and volume-located autocatalytic formation of GeTe and Ga 2 Te 5 crystallites. Similar crystallization activation energies were obtained by DSC and TMA. Direct comparison of the DSC and TMA data reveals that only a narrow temperature window of approx. 20 °C exists between the start of the glass softening and first formation of Te crystallites, which makes knowledge of crystallization kinetics crucial for the industrial glass processing and real-life commercial applications. Structural relaxation kinetics was described in terms of the Tool-Narayanaswamy-Moynihan (TNM) model. Good agreement between the relaxation activation energies determined by DSC and TMA was obtained. Values of the parameters of the TNM model were interpreted with respect to the molecular structures determined by Raman spectroscopy and reverse Monte Carlo simulations. The stabilizing role of Ga was explained by its preferred bonding to the non-bonding p electrons of Te. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry was used to study enthalpy relaxation kinetics of the Ge20Te(80-y)Seyinfrared chalcogenide glasses for the compositional rangey = 0–8. The relaxation behaviour was described in terms of the phenomenological Tool–Narayanaswamy–Moynihan (TNM) model. The direct curve-fitting procedure was used to determine the values of TNM parameters. Compositional evolution of the TNM parameters was interpreted with respect to the involved structural entities and their motions. Based on the joint Raman scattering study, the addition of Se leads to increased amount of edge-shared GeTe4-xSextetrahedra. While the primary structural basis for the relaxation movements appears not to be affected by addition of Se (constant value of non-linearity), changes of the non-exponentiality parameter indicate increased structural variability occurring within the groups of directly interlinked tetrahedra, which were found to carry the main portion of relaxation movements. Increased activation energy was explained by the presence of significantly stronger Ge–Se bonds and increased amount of edge-shared tetrahedra. [ABSTRACT FROM PUBLISHER]

Differential scanning calorimetry was used to investigate the effect of initial partial crystallinity on the non-isothermal nucleation-growth Johnson-Mehl-Avrami kinetics – selected Se-Te chalcogenide glasses were used as model systems. Different reproducible degrees of initial crystallinity were achieved by non-isothermal heating to a selected temperature. In case of the materials that primarily crystallize from mechanically induced defects, no change of the activation energy or kinetic mechanism was observed with increasing degree of initial crystallinity. On the other hand, material that showed complex crystallization behavior consisting from two competing overlapping crystal growth processes originating from volume-located nuclei and mechanical defects, respectively, exhibited marked shift in the dominance between the two kinetic mechanisms. In particular, with the increasing degree of initial crystallinity the defects-based crystallization mechanism started to dominate over the classical classic-nucleation-theory-based nucleation-growth crystallization mechanism. Increased amount of defects-based crystallization centers formed during the primary pre-crystallization appears to be the key factor for this change of the kinetic mechanism, rather than decreased activation energy (associated with the already existing crystal/glass interface) accelerating the actual crystal growth micro-mechanism. [ABSTRACT FROM AUTHOR]

Influence of particle size on relaxation and crystallization behavior of the Ge 20 Se 4 Te 76 chalcogenide glass was studied by differential scanning calorimetry (DSC). The structural relaxation kinetics was described by means of the Tool–Narayaswamy–Moynihan (TNM) model; it was found that the structural relaxation processes are not influenced by powder particle size or by the mechanically induced defects and heterogeneities originating from the grinding procedures — the evaluated TNM parameters were constant for all tested powders. On the other hand, the crystallization kinetics of the Ge 20 Se 4 Te 76 glass was found to be significantly influenced by the powder size. While the coarser powders exhibited a single-peak behavior corresponding to the nucleation-growth Johnson–Mehl–Avrami (JMA) kinetics, the crystallization of finest powders proceeded in two distinct steps. XRD analysis identified the two DSC signals as crystallization of hexagonal Te and rhombohedral GeTe, indicating that large amounts of mechanically induced defects accelerate the Te precipitation. Regarding the overall thermal characterization, the evaluated glass-stability criteria have shown that although the studied chalcogenide glass is a very good glass-former, its stability largely depends on the sample form. [ABSTRACT FROM AUTHOR]

Kinetic processes (cold crystallization and structural relaxation) occurring in the Ge 20 Te 76 Se 4 infrared bulk glass were studied by means of differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The crystallization behaviour was described in terms of the Autocatalytic and Johnson–Mehl–Avrami kinetic models. The crystallization activation energies evaluated by the two techniques were: 164 ± 7 kJ mol − 1 (DSC) and 153 ± 8 kJ mol − 1 (TMA). The agreement between the two values was explained in terms of the marked glass stability and glass-forming ability of the Ge 20 Te 76 Se 4 glass, where the crystal growth proceeds at rather low viscosities. Regarding the process complexity, increasing heating rate led to a decrease of the dimensionality of the formed crystallites (3D → 2D). Structural relaxation kinetics was described in terms of the Tool–Narayanaswamy–Moynihan model. Values of the parameters of the TNM model were interpreted with respect to the molecular structures determined by Raman spectroscopy. The Se ↔ Te substitution appears to lead to larger interconnection between the GeTe 4 tetrahedral chains rather than to significant changes in the intra-chain bonding. Good agreement between the activation energies of the relaxation process determined by the two experimental techniques was again obtained: 501 ± 10 kJ mol − 1 (DSC) and 490 ± 34 kJ mol − 1 (TMA). [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry, thermomechanical analysis and Raman spectroscopy were used to study the role of the Li 2 O and P 2 O 5 oxides on the structural relaxation phenomena in the Li-doped 45S5 Bioglass. The glass transition behavior was found to be similar for the enthalpy and volume manifestations of the relaxation motions. The Tool-Narayanaswamy-Moynihan (TNM) model was applied. An improved simulation-comparative methodology was used to determine the model relaxation parameters. The TNM model parameters and the selected glass transition characteristics (the glass transition temperature and the coefficients of thermal expansion) showed no statistically significant correlation with the particular elements present in the synthesized glasses. Hence, the information about the glasses composition was used to calculate the theoretical amounts of the Qn Si species in the Li-doped 45S5 glasses. It was found that practically all explored physico-chemical quantities related to the glass transition kinetics show a correlation with the content of Q2 Si species that are responsible for the formation of the chain-like structures in the present glasses. [ABSTRACT FROM AUTHOR]

The thermal behavior of thin selenium–tellurium (Se–Te) films was studied under non-isothermal conditions using differential scanning calorimetry; full binary compositional range was investigated. Based on the glass transition, crystallization and melting data the decreasing glass-forming ability in the Se–Te chalcogenide system was described by using a novel glass-forming ability (GFA) criterion. The glass transition kinetics of the as-prepared thin films was found to change with increasing Te content; namely the activation energy of structural relaxation processes decreased from 355 to 245 kJ mol −1 within the given compositional region. In the glass-forming region (at approx. 0–30% Te) the GFA and relaxation data obtained for the thin films correlated very well with the results for bulk glasses. Furthermore, the kinetics of crystallization were studied and described in terms of the Johnson–Mehl–Avrami nucleation-growth model. The apparent activation energy of crystallization was found to increase with Te content, changing from 115 to 170 kJ mol −1 in the given compositional range. Two-dimensional growth of crystallites, consistent with the idea of sterically restricted crystallization in a thin layer, was confirmed for the Se-rich compositional region. Further addition was found to lead to increased process complexity due to the formation of smaller, volume-located crystallites. In the glass-forming region, the crystallization kinetics of thin films corresponded to that determined for very fine Se–Te powders. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry was used to study enthalpy relaxation kinetics of the GeTe 4 infrared chalcogenide glass. The relaxation behavior was described in terms of the phenomenological Tool–Narayanaswamy–Moynihan (TNM) and Adam–Gibbs–Scherer (AGS) models. The direct curve-fitting procedure was found to provide the most accurate results under the assumption that high-quality DSC data are obtained and the correct pre-fitting treatment is applied. The recently developed novel evaluation of Δ h ⁎ from CR cycles and the improved simulation-comparative methodology were then found to provide the best results out of the tested non-fitting methods. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry (DSC) was used to study the crystallization behaviour in a selenium–tellurium (Se–Te) glassy system under isothermal conditions. The particle-size-dependent isothermal crystallization kinetics were described in terms of the Johnson–Mehl–Avrami (JMA) nucleation-growth model. The complexity of the crystallization process was found to be represented by overlapping competing surface and bulk nucleation-growth mechanisms. Based on the deconvolution in terms of the JMA model, the particular crystal growth processes were identified, and the interpretation of their physical origins was performed. Presence of the A and B types of spherulitic crystallites was confirmed; the temperature range of the transition in-between these two spherulitic forms was determined to be similar as for pure selenium. Increasing tellurium content was found to cause an increase of the apparent activation energy of the overall crystallization process as well as a gradual increase of the dominance of the CNT (classical nucleation theory)-based volume-located crystal growth over the surface crystallization, which originates from mechanically induced heterogeneities. [ABSTRACT FROM AUTHOR]

The utilization of the constant heating rate cyclic temperature history was examined with respect to enthalpy relaxation studies. In this regard, three main methodologies for the determination of structural relaxation parameters were described in detail — curve-fitting, simulation-comparative methods and determination of activation energy according to Moynihan. Advantages and disadvantages of the constant heating rate cycles were introduced for each of the methodologies. In addition, Moynihan's method was extensively tested for all types of relaxation behavior and its accuracy has been determined. Main emphasis was then put on the utilization of the unique shape of the constant heating rate cycles for the identification of certain data-distortive effects caused by erroneous experimental operations. A discussion of all possible data-distortive effects was conducted; the manifestation of these distortions with respect to the relevant evaluation methodologies was demonstrated on theoretically simulated data. For each data-distortive effect, a universal and easy-to-apply practice was suggested to recognize and account for the given data-distortion. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry was used to study nucleation behavior in As 2 Se 3 glass, dependent on particle size. The nucleation process was examined for a series of different coarse powders; the nucleation rate was estimated from the proportion of the crystalline material fraction. The enthalpy of fusion was utilized in this respect, and a correlation between Δ H m and Δ H c was confirmed. Two mechanisms of nucleus formation were found: classical heterogeneous nucleation (following CNT) and so-called “activation” of mechanically-induced defects. The latter appears to represent rapid formation of crystallization centers from a damaged glassy structure, where complete saturation occurs for fine powders in the range of 195–235 °C. A high amount of mechanical defects, on the other hand, was found to partially suppress the CNT nucleation process. [ABSTRACT FROM AUTHOR]