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.     

Estimation of the parameter of the main equation of the glass transition of amorphous polymers and other amorphous substances

Parameter C from the main glass-transition equation qτ_g = C according to Nemilov’s theory has the meaning of temperature bandwidth δT_g in which the freezing of the structure of the glass-forming liquid occurs (where q is the cooling rate of a melt and δ_g is the time of structural relaxation at the glass-transition temperature). The currently used method to estimate C results in inflated values, a circumstance that is due to the assumption of the constancy of the activation energy of the glass transition in the derivation of the calculation formula. Methods of estimation of C that are in agreement with the experimental data have been considered. A calculation of the time of structural relaxation, δ_g, on the basis of the values of the parameters of the Williams–Landel–Ferry equation has been proposed.     

First-order phase transformation and structural studies in Se<Subscript>85</Subscript>In<Subscript>15−x</Subscript>Zn<Subscript>x</Subscript> chalcogenide glasses

Present research work describes the crystallization kinetics and structural studies in Se₈₅In_15?xZn_x chalcogenide glasses. Bulk alloys of Se₈₅In_15?xZn_x were synthesized by melt-quenching procedure. High resolution X-ray diffraction (HRXRD) was used to confirm the amorphous nature of synthesized samples. Non-isothermal differential scanning calorimetry (DSC) measurements were performed at 5, 10, 15, 20 and 25 K min^?1 heating rates to study kinetics of crystallization in Se₈₅In_15?xZn_x. Various crystallization parameters such as glass transition (T _g), onset crystalline (T _c), peak crystallization (T _p) and melting temperature (T _m) were calculated from DSC curves. The activation energies of structural relaxation (ΔE _t) and crystallization (ΔE _c) were determined by using Kissinger, Moynihan and Ozawa approaches. ΔE _t is found to be the lowest for Se₈₅In₆Zn₉ sample which shows this sample has the highest probability of escape to a state of lower configurational energy and has greater stability. Thermal stability of various compositions was studied and found to vary with Zn content. Further, HRXRD and field emission scanning electron microscope were used for the study of first phase transformation in Se₈₅In_15?xZn_x samples.     

Method for calculating the sizes of nucleation centers upon homogeneous crystallization from a supercooled liquid

An alternative approach to calculating critical sizes l_k of nucleation centers and work A_k of their formation upon crystallization from a supercooled melt by analyzing the variation in the Gibbs energy during the phase transformation is considered. Unlike the classical variant, it is proposed that the transformation entropy be associated not with melting temperature T_L but with temperature T < T_L at which the nucleation of crystals occurs. New equations for l_k and A_k are derived. Based on the results from calculating these quantities for a series of compounds, it is shown that this approach is unbiased and it is possible to eliminate known conflicts in analyzing these parameters in the classical interpretation.     

Density,Viscosity, and Glass Transition of an Ethylenediamine–Ethylene Glycol Binary System

Densities ρ and viscosities η were measured for the binary mixtures of ethylenediamine (EDA) and ethylene glycol (EG) in the temperature range 288.15–323.15 K for ρ and at 273.15–323.15 K for η, both of which are broader temperature ranges than those reported previously. The value of ρ monotonously decreases against the mole fraction of EDA, x _EDA, and increasing temperature. The concentration dependence of η exhibits a maximum in the intermediate concentration range at all temperatures measured. The glass transition temperature, T _g, for samples with x _EDA < 0.7 was measured using differential scanning calorimetry. The measured T _g values show a peak in the intermediate concentration range, which is a behavior similar to that of η; however, the peak concentrations for η and T _g did not precisely align because of a deviation in the maximum hydrogen-bond density. The partial molar volumes for EDA and EG and the thermal expansivities, α, were obtained from ρ. Results in the present study are discussed in terms of the extensively increasing hydrogen-bond density for polyamine–polyhydric alcohol systems.     

Solid solutions (Ru,Nb)Sr<Subscript>2</Subscript>(Sm<Subscript>1.4</Subscript>Ce<Subscript>0.6</Subscript>)Cu<Subscript>2</Subscript>O<Subscript>10−δ</Subscript>: Synthesis,structure, and properties

Solid solutions of as-batch composition (Ru_1?x Nb _x )Sr₂(Sm_1.4Ce_0.6)Cu₂O_10?δ (the Ru,Nb)-1222 phase), where x = 0.0, 0.25, 0.50, 0.75, or 1.00, have been synthesized and characterized by X-ray diffraction. A correlation is proposed between the refined composition of the Ru-1222 and Nb-1222 phases and their structural features. With increasing oxygen concentration in the Ru-1222 phase, the superconducting transition temperature increases from T _c = 28 to T _c = 34 K. The composition and magnetic properties of the Ru-1222 phase are affected by the batch composition: unlike in Ru + RuO₂ mixtures, the presence of ruthenium in the batch decreases the oxygen proportion and increases the magnetic ordering temperature T _m; the phase of as-batch composition NbSr₂(Sm_1.4Ce_0.6)Cu₂O_10?δ is paramagnetic.     

The Temperature Effect on the Transport Properties of 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids

The temperature dependences of specific and equivalent conductivities, viscosity, density, and crystallization temperature are determined for three 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C _n MeIm] [Tf₂N], n = 2, 3, 4) ionic liquids saturated with water vapor at room temperature. It is established that in the area of positive temperatures, the relationship between viscosity and conductivity obeys the fractional Walden rule with exponents of 0.97, 0.92, and 0.92 for ionic liquids with ethyl-, propyl-, butylradicals, respectively. The temperature dependences of conductivity and viscosity are approximated using the Vogel–Fulcher–Tammann equation (R² > 0.999), and ideal glass transition temperatures T₀ are calculated for the investigated liquids. The obtained values of T₀ depend largely on the chosen range of temperatures. It is shown that [C₂MeIm][Tf₂N] occupies a separate position with regard to [C₃MeIm][Tf₂N] and [C₄MeIm][Tf₂N].     

Thermal and dielectric characterization of multi-walled carbon nanotubes−thermoplastic polyurethanes composites

Multi-walled carbon nanotubes–thermoplastic polyurethanes composites were characterized by means of differential scanning calorimetry and dielectric relaxation spectroscopy. The composite is characterized by two glass transition temperatures T _g . The T _g associated with the soft segment decreases by increasing of carbon nanotubes content, while carbon nanotubes content has practically no effect on the value of the T _g associated with the hard segments. It was observed that rising the temperature and carbon nanotubes content resulted in the increased of both the dielectric permittivity and the loss factor. The presence of carbon nanotubes produces an enhancement of charge carriers trapping, increasing the electrical conductivity. The electrical conductivity of the composite was found to exhibit an insulator to conductor transition at a carbon nanotubes critical content, i.e., the percolation threshold, near 6 wt %.     

Concentration,temperature, and isotopy effects on the heat capacity of aqueous urea

Relations for the apparent molar heat capacity ?_c of urea in an aqueous solution depending on the molality m and temperature were obtained. A transition to the relations ?_c(m,T) for D₂O-(ND₂)₂CO and T₂O-(NT₂)₂CO systems was effected by temperature scaling. At low temperatures, the isotherms of the molar heat capacity C _p(m) of the protium and deuterium systems have minima shifted to more dilute solutions at elevated temperatures. At m = 1, C _p of a solution does not depend on temperature in both systems. The dependences C _p(T) also have minima at constant concentrations. The temperature of the minimum heat capacity is most effectively lowered by small additions of urea. For m = 0.25, T _min is 7.5 K lower than T _min of pure water, and its heat capacity is 0.08 J/(mol K) higher. A transition from m = 1.5 to m = 2 lowers the temperature of the minimum heat capacity by 3.6 K; thus, the heat capacity of solutions differs by 0.02 J/(mol K) only.     

Effect of mechanical activation on the hydrogen reduction kinetics of magnetite concentrate

The combined thermal analysis techniques thermal expansion: and differential scanning calorimetry were used to characterize various phase transitions that exist in the solid solutions of PbZr_1?xSn_xO₃. Using thermodynamic quantities, i.e., thermal expansion and specific heat to distinguish first-order transitions from second-order ones, we demonstrate that some perovskite antiferroelectrics can exhibit continuous transition at their Curie temperature T _C. We observed such a transition in antiferroelectric crystals of solid solutions based on PbZrO₃. Although pure PbZrO₃ is a classical example of antiferroelectric crystal with a first-order transition at T _C, the solid solutions of PbZr_1?xSn_xO₃ in the range of composition of x > 0.25 seem to exhibit a second-order phase transition.     

Molecular statistical model of spin crossover equilibrium in the crystal state taking into account the phenomenon of ordering

Formalism is developed in which contributions of binary and ternary interactions towards free energy of a mixture of low-spin (A) and high-spin (B) isomers of spin crossover compounds as well as effects of ordering are taken into account. Parameters characterising non-ideality in this formalism are the excess free energy (ΔF _ex) and absolute asymmetries (Δ ^A , Δ ^B ) of splittings of free energy levels. The excess free energy characterises the effects of binary interactions whereas asymmetries arise from ternary interactions. According to this model, the plateau in the spin crossover transition curve originates from the phenomenon of ordering taken into account in the Gorsky-Bragg-Williams approximation.     

Effect of Ag addition on crystallization kinetics and thermal stability of As–Se chalcogenide glasses

Chalcogenide glasses of (As₅₀Se₅₀)_100?xAg_x (0 ≤ x ≤ 25) were prepared using the melt quenching technique under non-isothermal conditions. Differential scanning calorimetry curves measured at different heating rates (5 ≤ β ≤ 40 K min^?1) are used to characterize the as-quenched samples. The thermal stability was monitored through the calculation of the temperature difference T _c ? T _g, stability parameter S and crystallization rate factor K _p. The glass-forming ability (GFA) was investigated on the basis of Hurby parameter H _r which is a strong indicator of GFA. In addition, the activation energy of glass transition E _t, activation energy of crystallization E _c and Avrami exponent n of the studied compositions were determined. The mechanism of crystallization was found to be a combination of two- and three-dimensional crystal growth.     

Temperature-dependent AC electrical conductivity,thermal stability and different DC conductivity modelling of novel poly(vinyl cinnamate)/zinc oxide nanocomposites

Thermal analysis on organically modified Ca²⁺-montmorillonite (OMON) and its source materials—octadecylamine (ODA) and Ca²⁺-montmorillonite (Ca²⁺-Mon)—was studied using thermally stimulated current (TSC) technique. The appearance of ρ _MON peak with the T _max = 75 °C shows the ability of the developed TSC system to demonstrate the relaxation effects of dehydration in Ca²⁺-Mon. It appeared within the temperature range of DSC endothermic peak (30–100 °C) where the T _mMON = 58 °C. Segmental motions of ODA chains and structural disruptions in the modifier agent compound produced TSC α _ODA, ρ _ODA and ρ _1ODA peaks that are comparable to thermal transition and endothermic peaks in DSC profile (T _gODA, T _m1ODA and T _m2ODA). The effect of localized motion in ODA chains as revealed by the TSC β_OMON peak (T _max = ?23 °C), however, is absent in the DSC profile of OMON. It shows TSC technique has high sensitivity in detecting various relaxation behaviors at molecular level. More evidences are demonstrated by the ρ _OMON (T _max = 86 °C) and ρ _1OMON (T _max = 105 °C) peak originated from the ODA chains structures. These peaks also confirm the intercalation of the modifier cations inside the Ca²⁺-Mon gallery.     

Epr Spectroscopy of Adsorbed Spin-Labeled Peptides: Immobilization of Trichogin on the Titanium Oxide

The TOAC-spin-labeled peptide Trichogin GA IV adsorbed on the TiO₂ surface is studied. It is shown that the continuous wave (CW) electron paramagnetic resonance (EPR) spectrum does not depend on temperature in a wide range of 77–300 K. A pulsed EPR method of electron spin echo (ESE) utilizing a two-pulse sequence (π/2-τ-π) is used to study temperature dependence of the phase relaxation time, T_F. The T_F values are found to change from 750 ns to 100 ns in the interval of 77–300 K. The pulsed electronelectron double resonance (PELDOR) measurements utilizing the pulse sequence((π/2)_A,-T-π_B,-(τ-T)-π_A) show that the space distribution of spin labels on the surface remains uniform irrespective of the temperature, and provide the fractal dimension of the surface of 2.7±0.1. The obtained results testify that EPR pulse experiments can be used to study adsorbed spin-labeled molecules at room temperatures, i.e. not only at cryogenic temperatures.     

Peroxy radicals as motional probes at the end of isolated polystyrene chains and on the cellulose surfaces in vacuum

The isolated polystyrene chains spin-labeled with peroxide radical at the free end (IPSOO) in which the chain roots were covalently bonded to the surface of microcrystalline cellulose (MCC) powder were produced by mechanochemical polymerization of styrene initiated by MCC mechanoradicals. The IPSOO was used as motional probes at the ends of isolated polystyrene chains tethered on the surface of MCC powder. Two modes for the molecular motion of IPSOO were observed. One was a tumbling motion of IPSOO on the MCC surface, defined as a train state, and another was a free rotational motion of IPSOO protruding out from the MCC surface, defined as a tail state. The temperature of tumbling motion (T _tum ) of IPSOO at the train state was at 90 K with anisotropic correlation times. T _tum (90 K) is extremely low compared to the glass transition temperature (T _g ^b ; 373 K) of polystyrene in the bulk. At temperatures above 219 K, the IPSOO was protruded out from the MCC surface, and freely rotated at the tail state. The train–tail transition temperature (T _train–tail ) was estimated to be 222 K. T _tum (90 K) and T _train–tail (222 K) are due to the extremely low chain segmental density of IPSOO on the MCC surface under vacuum. The interaction between IPSOO and the MCC surface is a minor contributing factor in the mobility of IPSOO on the surface under vacuum. It was found that peroxy radicals are useful probes to characterize the chain mobility reflecting their environmental conditions.     

Diffusion of hydrogen atoms and the internal friction spectrum of the PdH<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> system

The temperature dependences of dissipative loss spectra were studied by the internal friction method for the polycrystalline Pd system and interstitial solid solutions PdH _x . Four relaxation processes related to the structural peculiarities of the crystal lattice were observed in Pd; two additional relaxation processes were observed in PdH _x solid solutions. The latter were related to the mobility of hydrogen atoms in different phases of the face-centered cubic crystal structure.     

Spin-lattice relaxations study of water mobility in natural natrolite

The mobility of water molecules in natural natrolite (Na₂Al₂Si₃O₁₀?2H₂O) is investigated by the ¹H NMR method. The spin-lattice relaxation times in the laboratory and rotating frames (T₁ and T_1ρ) are measured as a function of the temperature for a polycrystalline sample. From experimental T₁ data it follows that at T > 286 K the diffusion of water molecules along channels parallel to the c axis is observed. From experimental T_1ρ data it follows that at T > 250 K the diffusion of water molecules in transversal channels of natrolite is also observed. At a low temperature (T < 250 K) the dipolar interaction with paramagnetic impurities (presumably Fe³⁺ ions) becomes significant as a relaxation mechanism of ¹H nuclei.     

Phase equilibria involving solid solutions in the Li–Mn–O system

Phase equilibria involving LiMn₂O_4-, Li₂MnO_3-, LiMnO_2-, Mn₃O_4-, and MnO-base solid solutions were studied with varied temperature and partial oxygen pressure. The \({P_{{o_2}}}\)–T and x–y projections of the P–T–x–y phase diagram of the Li–Mn?O system were constructed, as well as the key x–y isotherms of the Li₂O–MnO–MnO₂ quasi-ternary system. In some experiments, the authors’ hydride lithiation method was employed to prepare lithium-rich homogeneous three-component nonstoichiometric phases.     

Production and characteristics of substituted lanthanum niobate LaNb<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>W<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4 + δ</Subscript>

Solid solutions LaNb_1–x W _x O_{4 + δ} (x = 0.02–0.10, Δx = 0.02) were investigated, which crystallize in the monoclinic system (space group I2/c) at room temperature and undergo a phase transition into the tetragonal modification with increasing temperature. The stability of various modifications was analyzed by high-temperature X-ray powder diffraction analysis. The electrical conductivity of sintered samples was studied by impedance spectroscopy. Insertion of tungsten into the niobium sublattice leads to an increase in the conductivity of the solid solutions.     

High-temperature heat capacity and thermodynamic properties of pyrovanadate Pb<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> and orthovanadate Pb<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The heat capacities of Pb₂V₂O₇ and Pb₃(VO₄)₂ as a function of temperature in the range 350–965 K have been studied by the differential scanning calorimetry method. The C_P = f(T) curve for Pb₂V₂O₇ is described by the equation C_p = (230.76 ± 0.51) + (73.60 ± 0.50)×10^-3T ? (18.38 ± 0.54)×10⁵T^-2 in the entire temperature range. For Pb₃(VO₄)₂, there is a well-pronounced extreme point in the C_P = f(T) curve at T = 371.5 K, which is caused by the existence of a structural phase transition. The thermodynamic properties of the oxide compounds have been calculated.