Reversible phase transition in vanadium oxide films sputtered on metal substrates

Vanadium oxide films, deposited on aluminium (Al), titanium (Ti) and tantalum (Ta) metal substrates by pulsed RF magnetron sputtering at a working pressure of 1.5 x10^?2 mbar at room temperature are found to display mixed crystalline vanadium oxide phases viz., VO₂, V₂O₃, V₂O₅. The films have been characterized by field-emission scanning electron microscopy, X-ray diffraction, differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy, and their thermo-optical and electrical properties have been investigated. Studies of the deposited films by DSC have revealed a reversible-phase transition found in the temperature range of 45–49 °C.     

Thermal behaviour of polystyrene/silica composites

The particle-size distribution in silica powder prepared by the sol–gel method has been determined by dynamic light scattering analysis. The average diameter of the particles was found to be 250?nm. Using a low-temperature nitrogen adsorption–desorption technique, it was found that the synthesised powder may be referred to as mesoporous materials. Polystyrene/silica composite films were fabricated by casting from o-xylene solutions. It was found, using thermogravimetry, that incorporation of silica leads to an increase in both the onset temperature of polymer degradation and in the temperature at which the maximum rate of weight loss occurs. Using differential scanning calorimetry, the phase transitions from the glassy state to the elastic one were studied for the polymeric materials. New data relating to the effect of silica on the glass-transition temperature, T_g, of composites with a low weight fraction of SiO₂ were found. Specifically, we found a non-monotonic concentration dependence of the value of T_g. The present results advocate for employing silica as an effective filler for producing polymer composites with enhanced thermal properties.     

Composition dependence of the activation energy of the glass transition in some chalcogenide glasses

The activation energy (E _t) of the glass transition process has been obtained for glassy Se_{80? x} Te₂₀M _x (M = Ag, Cd, In, Sb) and Se_{100? x} M _x (M = In, Te, Sb) systems using differential scanning calorimetry. The composition dependence of E _t is explained in terms of fragility index for the systems. A reversal in the trend of the E _t is explained using topological models.     

Effect of lithium-ion irradiation on the crystallization kinetics of glassy Se98In2

Differential scanning calorimetry (DSC) has been used to study the crystallization kinetics of glassy Se₉₈In₂ both before and after irradiation of the alloy with high-energy (50 MeV) lithium ions. After the ion-irradiation, significant changes in the kinetic parameters of crystallization of the glass were observed. The results are explained in terms of a model involving irradiation-induced defects.     

Determination of glass-forming ability of Ge1− x Sn x Se2.5 (0 ≤ x ≤ 0.5) alloys using differential scanning calorimetry

The glass-forming ability of Ge_{1? x} Sn _x Se_2.5 (0 ≤ x ≤ 0.5) alloys was studied using differential scanning calorimetry. Samples were scanned at different heating rates under non-isothermal conditions. Various simple quantitative methods were employed to assess the stability of the glassy materials in the above-mentioned system. All of these methods are based on characteristic temperatures, such as the glass-transition temperature, T _g, the onset-of-crystallization temperature, T _c, and the peak crystallization temperature, T _p. A crystallization rate factor, K, has also been used as a measure of the thermal stability of the glasses. It was found that Ge_0.7Sn_0.3Se_2.5 was the least stable among all the samples.     

The crystallographic structure of λ transition-alumina compared with the periodic antiphase boundary structure of a Ga2O3-rich Mg gallate

One of the high-temperature metastable phases found in the MgGa₂O₄–Ga₂O₃ system is the ε_Mg non-stoichiometric Mg gallate. It has a one-dimensional periodic antiphase boundary (PAPB) structure based on the spinel structure. The APBs are parallel to the {3?1?0} planes and the APB vectors are of the 1/4?1 1 0? type when referred to the spinel structure. This generally leads to the existence of 12 monoclinic twin variants in the studied samples. By comparing the X-ray or electronic diffraction patterns of both phases, it will be shown that the recently discovered?λ?transition-alumina has the same type of structure.     

Thermal behaviour of poly(methyl methacrylate)/fullerene composite films

ABSTRACT

Poly(methyl methacrylate) films and poly(methyl methacrylate)/fullerene composite films were fabricated by casting from toluene solutions. The mass fraction of fullerene (C₆₀) was varied from 0.05–3?wt. %. The effect of the fullerene (C₆₀) content on the thermal degradation parameters of the composite films was evaluated by thermogravimetric (TG) analysis. It was found that the incorporation of C₆₀ improved the thermal stability of the polymers. The films eventually decomposed in three stages. Incorporation of fullerene caused a change in the distribution of mass loss over the stages of degradation in comparison with the pristine polymer. Using differential scanning calorimetry (DSC), the phase transitions from the glassy state to the elastic one was studied for the examined polymeric materials. New data relating to the effect of C₆₀ on the glass transition temperature of composites with low weight fractions of filler were obtained. Specifically, for films containing up to 0.1 wt. % of C₆₀, a single glass transition temperature was found, whereas for composites with a higher concentration of filler, two glass transition temperatures were recorded.     

Glass formation in the Pd–Si-based alloys

Taking into account the importance of undercooling on glass formation, we propose a new criterion which allowed us to predict the best glass-forming composition, namely Pd₇₈Ag_5.5Si_16.5, among selected Pd–Si-based alloys ranging from binary to quaternary systems. The composition agrees well with that found experimentally. Using conventional copper mould casting, the Pd₇₈Ag_5.5Si_16.5 alloy is capable of forming fully amorphous rods with a diameter of 3 mm. The effects of Au and Ag additions on the glass-forming ability of the selected Pd–Si-based alloys have been investigated.     

Thermal stability and glass-forming ability of Se80− x Te20Ag x (x = 0, 3, 5, 7 and 9) chalcogenide glasses

The thermal stability and glass-forming ability (GFA) of Se_{80? x} Te₂₀Ag _x (x?=?0,?3,?5,?7 and 9) chalcogenide glasses have been investigated using differential scanning calorimetry (DSC). The DSC runs have been taken at five different heating rates (10, 20, 30, 40 and 50?K/min) under non-isothermal condition. The thermal stability and GFA are monitored through determination of the temperature difference ΔT?=?T _c???T _g, where T _c is the onset crystallization temperature, T _g is the glass transition temperature, H ^l is the stability parameter, ΔH _c is the enthalpy released during crystallization and F _i is the fragility index. The activation energy of crystallization E _c and crystallization rate factor K have also been determined as indicators of the thermal stability of the above-mentioned samples. It is found that Se₇₁Te₂₀Ag₉ is the most stable among all the samples of the series.     

Formation of metastable phase and its influence on the solidification microstructure of highly undercooled eutectic Fe40Ni40B20 alloy

Solidification of a highly undercooled eutectic Fe₄₀Ni₄₀B₂₀ alloy melt has been studied by high-speed video in combination with an analysis of the temperature history. The metastable phase with a colony shape structure solidified primarily from the melt. DSC analysis confirmed the formation of the metastable phase. The metastable phase was re-melted, transformed or decomposed into stable phases during further solidification or cooling processes, and gave birth to the final as-solidified structures. On this basis, the effects of the metastable phase formation and transformation on evolution of the as-solidified structure is described.