Annealing kinetics of gold and iron–gold complex

Thermally induced defects in heat treated and then quenched in water n-silicon samples have been studied using deep level transient spectroscopy. Two deep levels at energies E _c-0.55 eV, and E _c-0.23 eV are observed in high concentration. The emission rate signature and annealing characteristics of energy state E _c-0.55 eV identify it as Au(A). During annealing a level emerges at energy position E _c-0.35 eV. This level has been identified as Au–Fe complex. Au(A) and Au–Fe showed an interesting reversible reaction in temperature range 175 °C–325 °C which follows the following theoretical relation that adds a new parameter in identifying Au(A) and Au–Fe complex.

Densities and Volumetric Properties of Binary Mixtures of Butyl Acrylate with Benzene, Toluene, o-Xylene, m-Xylene, p-Xylene, and Mesitylene at Temperatures from 288.15?K to 318.15?K

The densities, ρ, of binary mixtures of butyl acrylate (BA) with benzene, toluene, o-xylene, m-xylene, p-xylene, and mesitylene, including those of pure liquids, over the entire composition range were measured at the temperatures (288.15, 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15) K and atmospheric pressure. From the experimental data, the excess molar volumes, V_m^E{V_{\rm m}^{\rm E}} were calculated. The V_m^E{V_{\rm m}^{\rm E}} values were negative over the whole composition range for all the mixtures and at each temperature studied, except for BA + mesitylene which exhibit positive V_m^E{V_{\rm m}^{\rm E}} values, indicating the presence of specific interactions between BA and aromatic hydrocarbon molecules. The deviations in V_m^E{V_{\rm m}^{\rm E}} values follow the order: benzene<toluene<p-xylene<m-xylene<o-xylene<mesitylene. It is observed that V_m^E{V_{\rm m}^{\rm E}} values depend upon the number and position of the methyl groups in these aromatic hydrocarbons.     

Dominancy of antiferromagnetism in Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O diluted magnetic semiconductors

The outline of magnetic interactions in DMSs was determined using Zn_1−x Co _x O particles, where “x” was changed as 0.01, 0.05, 0.10, 0.15, and 0.20. The syntheses were accomplished though mechanical milling and thermal treatment, known as solid state reaction. The formation of each synthesis was monitored by differential thermal and thermo gravimetric methods (DT-TGA). Substitution of Co²⁺ ions with Zn²⁺ host atoms in a ZnO lattice was analyzed using X-ray diffraction (XRD) patterns, Fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray spectrometry (EDS) data, transmission electron microscopy (TEM) figures, scanning area electron diffraction (SAED) patterns, and X-ray photo spectroscopy (XPS) spectrum. The measured Co contents in ZnO lattice were found to be ~0.7% less than the expected result. In addition to Zn_1−x Co _x O particles, tungsten (W) contaminations were noticed in the variations of 1.5 ± 0.2%, as originating from the abrasion between the miller and balls. The progressive replacement of Co²⁺ with Zn²⁺ host ions in ZnO lattice from 1% to 20% decreased the band edge from 3.03 ± 0.01 eV to 2.95 ± 0.01 eV, respectively. Co doping has also changed the magnetic nature of the ZnO. Although having both interactions (ferromagnetic and antiferromagnetic), dominance of ferromagnetic behavior was only observed for Zn_0.99Co_0.01O with the coercivity of ~154 ± 50 Oe and positive Curie–Weiss temperature as 79 ± 1 K. However, the calculated \frac2J_\textex k_\textB {\frac{{2J_{\text{ex}} }}{{k_{\text{B}} }}} values have proved that the higher Co²⁺ concentrations in ZnO lattice have increased the efficiency of antiferromagnetic interactions. Surprisingly, there was no rapid change at \frac2J_\textex k_\textB {\frac{{2J_{\text{ex}} }}{{k_{\text{B}} }}} values as mentioned in previous works.     

Diffusivity and solubility of oxygen in solid palladium

The solid solubility c _O of oxygen in palladium in equilibrium with gaseous oxygen has been determined from absorption-desorption experiments for temperatures T of 1123 and 1173 K and oxygen partial pressures between 2.7 × 10³ and 4.0 × 10⁴ Pa. The relationship between c _O, and T is given by , where R = 8.314 JK⁻¹ mol⁻¹ is the universal gas constant, ΔH _s = −13.55 kJ/mol denotes the heat of solution of oxygen in palladium and the constant a amounts to or . The diffusion coefficient D _O of oxygen in solid palladium has been determined by incomplete isothermal internal oxidation of Pd–Fe alloys using the data on the oxygen solubility in palladium. The temperature dependence of D _O obeys the Arrhenius equation D _O = D ⁰ exp(−E _d/RT) with pre-exponential factor D ⁰ = 2.33 × 10⁻⁷ m²/s and activation energy of diffusion of oxygen in palladium, E _d = 102.76 kJ/mol     

Synthesis and Optical Studies of Superconducting MgB2 Thin Films

Synthesis and optical transmission of MgB₂ thin films on optically transparent glass are reported. In the 400–1000 nm regime as deposited films show high metallic reflectivity and very little transmission. After deposition, the films were annealed ex situ and rendered superconducting with T _c of 38 K, approaching that of the bulk material. The reaction conditions where quite soft ∼10 min at 550°C. The optical absorption coefficient, α and photon energy, E followed a Tauc-type behavior, = _T (E - E_g )(\alpha E)^{1/2} = \beta _T (E - E_{\rm g} ). The band gap (E _g) was observed to peak at 2.5 eV; but, the slope parameter β _T behaved monotonically with reaction temperature. Our results indicate that an intermediate semiconducting phase is produced before the formation of the superconducting phase; also optical measurements provide valuable information in monitoring the synthesis of MgB₂ from its metallic constituents. In addition these films have interesting optical properties that may be integrated into optoelectronics.     

Barrier characteristics of Pt/Ru Schottky contacts on <Emphasis Type="Italic">n</Emphasis>-type GaN based on <Emphasis Type="Italic">I–V–T</Emphasis> and <Emphasis Type="Italic">C–V–T</Emphasis> measurements

We have investigated the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Ru/Pt/n-GaN Schottky diodes in the temperature range 100–420 K. The calculated values of barrier height and ideality factor for the Ru/Pt/n-GaN Schottky diode are 0·73 eV and 1·4 at 420 K, 0·18 eV and 4·2 at 100 K, respectively. The zero-bias barrier height (Φ_b0) calculated from I–V characteristics is found to be increased and the ideality factor (n) decreased with increasing temperature. Such a behaviour of Φ_b0 and n is attributed to Schottky barrier (SB) inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs) at the metal/semiconductor interface. The current–voltage–temperature (I–V–T) characteristics of the Ru/Pt/n-GaN Schottky diode have shown a double Gaussian distribution having mean barrier heights ( [`(F)]<sub>\textb0</sub> {\bar{{\Phi}}_{\text{b}0}} ) of 1·001 eV and 0·4701 eV and standard deviations (σ <sub>0</sub>) of 0·1491 V and 0·0708 V, respectively. The modified ln (J<sub>0</sub> /T<sup>2</sup> )-( q<sup>2</sup>s <sub>0</sub><sup>2</sup>/2k<sup>2</sup>T<sup>2</sup> ){ln} ({{J}_{0} /{T}^{2}} )-( {{q}^{2}{\sigma} _{0}^{2}/{2}{k}^{2}{T}^{2}} ) vs 10<sup>3</sup>/T plot gives [`(F)]_\textb0 \bar{{\Phi}}_{\text{b}0} and Richardson constant values as 0·99 eV and 0·47 eV, and 27·83 and 10·29 A/cm²K², respectively without using the temperature coefficient of the barrier height. The difference between the apparent barrier heights (BHs) evaluated from the I–V and C–V methods has been attributed to the existence of Schottky barrier height inhomogeneities.     

The effect of internal particle heat conduction on heat transfer analysis of turbulent gas–particle flow in a dilute state

In many cases the conduction mechanism inside a particle can not be ignored (large particles, low thermal conductivity and high porosity) during turbulent gas–particle flows. However, the accurate solution might be difficult to apply. Therefore, we first develop here the ability to conduct accurate solution and then we define the criterion for which the internal conductivity might be ignored. A combination between commercial C.F.D. code and user defined programs was developed to predict numerically the gas–particle velocity and temperature profiles. The selected criterion (defined at the outlet of the pipe’s cross-section), referred to the relation between the computational desirable average temperature difference without ignoring internal heat conductivity and the average particles temperature by ignoring internal heat conductivity, determines whether to consider the heat conduction mechanism in numerical simulations or to ignore it. It was found that the average particles temperature for T _p =  f(r) is lower than the case when T _p =  constant. Also, it was found that the non-dimensional temperature difference criterion is a continuous function of [Bi ×  (d _p/D)] for a specific geometry, various pipe and particle diameters, various particles’ thermal conductivities, constant heat flux and Re number. The numerical code enables to extend the classical criterion for Bi number of solids to various gas–particle systems and different operational conditions.     

Influence of heating atmosphere on the properties of stannous phosphate glass

A low-viscosity 60 SnO–40 P₂O₅ (mol%) glass was reheated at 280 °C (about 45 °C above the glass-transition temperature) for 20 min in various atmospheres (Ar, air, and O₂), then the structure- and surface-related properties were examined. It was found that increase in \textP_{\textO 2} {\text{P}}_{{{\text{O}}_{ 2} }} increases surface hardness, reduces optical transmittance, and improves chemical durability. The above phenomena are explained in terms of the increased oxidation tendency of Sn²⁺ to Sn⁴⁺ on the glass surface during reheating in increased \textP_{\textO 2} {\text{P}}_{{{\text{O}}_{ 2} }} .     

Mixed-mode crack-tip stress fields for orthotropic functionally graded materials

Quasi-static mixed mode stress fields for a crack in orthotropic inhomogeneous medium are developed using asymptotic analysis coupled with Westergaard stress function approach. In the problem formulation, the elastic constants E ₁₁, E ₂₂, G ₁₂, ν ₁₂ are replaced by an effective stiffness ${E=\sqrt {E_{11} E_{22}}}$ , a stiffness ratio ${\delta =\left({{E_{11}}\mathord{\left/ {\vphantom {{E_{11}} {E_{22}}}}\right. \kern-0em} {E_{22}}} \right)}$ , an effective Poisson’s ratio ${\nu =\sqrt {\nu_{12}\nu _{21}} }$ and a shear parameter ${k=\left({E \mathord{\left/ {\vphantom {E {2G_{12}}}}\right. \kern-0em} {2G_{12}}}\right)-\nu }$ . An assumption is made to vary the effective stiffness exponentially along one of the principal axes of orthotropy. The mode-mixity due to the crack orientation with respect to the property gradient is accommodated in the analysis through superposition of opening and shear modes. The expansion of stress fields consisting of the first four terms are derived to explicitly bring out the influence of nonhomogeneity on the structure of the mixed-mode stress field equations. Using the derived mixed-mode stress field equations, the isochromatic fringe contours are developed to understand the variation of stress field around the crack tip as a function of both orthotropic stiffness ratio and non-homogeneous coefficient.     

Equilibration kinetics of (La,Sr)MnO3

The present work reports isothermal changes of oxygen non-stoichiometry for the perovskite-type electrode material (La_0.8Sr_0.2)MnO₃ in the temperature range 945–1255 K. A thermogravimetric method was used to monitor the rate of the gas/solid equilibration. For equilibration degrees larger than 0.5, the equilibration kinetic data can be described by a diffusion equation. The determined chemical diffusion coefficient depends essentially on the oxygen partial pressure. Its temperature dependence can be expressed by the following expressions at low and high p(O₂), respectively:

Effects of oxygen partial pressure control on the microstructure and PTCR properties of Ho doped BaTiO<Subscript>3</Subscript>

Effects of oxygen partial pressure ( ) control on the electrical properties and microstructural development of (Ba_1-xHo_x)_0.997TiO₃ were studied. An oxidation condition ( ∼ 1.0 atm) was maintained during the heating process, and then the specimen was sintered in a reducing atmosphere ( < 10⁻⁹ atm) at 1350 °C, followed by the annealing process at 1000 °C and = 1 atm. The switching temperature (T_S) from the oxidation atmosphere to the reducing condition was changed from 1100 to 1350 °C. A significant decrease in the room-temperature resisitivity (ρ₂₅) was observed as T_S was increased. The temperature coefficient of resistance (TCR) was independent of the change in T_S, and closed pores decreased with increasing T_S.     

Determination of standard Gibbs energies of formation of ternary oxides in the system Co-Sb-O by solid electrolyte emf method

An isothermal section of the phase diagram of the system Co-Sb-O at 873 K was established by isothermal equilibration and XRD analyses of quenched samples. The following galvanic cells were designed to measure the Gibbs energies of formation of the three ternary oxides namely CoSb₂O₄, Co₇Sb₂O₁₂ and CoSb₂O₆ present in the system.

On the thermal stability of the copper–titanium–zirconium phosphate solid-solution series: CuTi2?xZrx(PO4)3 (0?≤?x?≤?2) under air

The solid copper(I) electrolytes: CuTi₂(PO₄)₃; CuTiZr(PO₄)₃; and CuZr₂(PO₄)₃; were prepared as powders by high temperature synthesis and analysed by powder XRD. These materials were then annealed in air at 400 °C for 72 h. The results of powder XRD showed that the degree of oxidation under these conditions varies progressively and enormously across this series, with the passivity dependent upon the Ti/Zr ratio; CuTi₂(PO₄)₃ being the least reactive under these conditions. The results of the thermogravimetric analyses in artificial air ( P_\textO2 P_{{{\text{O}}_{2} }}  = 0.2 bar) corroborate with the above, and reveal in all cases that T _eqm = 500 ± 25 °C for the reversible reaction: 4Cu (Ti, Zr)₂(PO₄)₃ + O₂ ⇆ 4Cu_0.5 (Ti, Zr)₂(PO₄)₃ + 2CuO. Green Cu_0.5TiZr (PO₄)₃ has been prepared as a new compound and was shown to belong to a rhombohedral system with hexagonal cell constants: a = 8.599(1) ?; c = 22.355(3) ?; Z = 6.     

Effect of Mn substitutions on dielectric properties of high dielectric constant BaTiO<Subscript>3</Subscript>-based ceramic

The effects of Mn added during processing on the dielectric properties and microstructure of the BaTiO₃-based ceramic materials system were discussed. Experiments show that a proper content of Mn can significantly increase dielectric constant (ε) and reduce the dielectric loss (tanδ) in BaTiO₃-based X7R ceramic materials. The results attribute to the reaction: . When the system doped with 0.046mol% MnCO₃ was sintered at 1240 °C for 4 h, the ε, tanδ and TCC were 5800, 1.6%, 0 ± 10% at 1 KHz respectively.     

Thermal characteristics and crystallization kinetics of tellurite glass with small amount of additive As<Subscript>2</Subscript>O<Subscript>3</Subscript>

The crystallization kinetics of the TeO₂/TiO₂/As₂O₃ glassy system was studied under nonisothermal conditions. The method was applied to the experimental data obtained by differential thermal analysis (DTA), using continuous-heating techniques. In addition, two approaches were used to analyze the dependence of glass transition temperature (T _g) on the heating rate (β): One is the empirical linear relationship between (T _g) and (β); The other approach is the use of straight line from the plot of ln( T_\textg² /b ) \textvs . 1/T_\textg \ln \left( {T_{\text{g}}^{2} /\beta } \right)\,{\text{vs}} .\,1/T_{\text{g}} for evaluation of the activation energy for glass transition. The crystallization results are analyzed, and both the activation energy of crystallization process and the crystallization mechanism are characterized.     

Interface structure and strain development during compression tests of Al2O3/Nb/Al2O3 sandwiches

The interface structure of an Al₂O₃/Nb/Al₂O₃ sandwich produced by solid-state diffusion bonding was investigated in detail by various transmission electron microscopy (TEM) methods. The joint possessed at one interface a , , and on the other interface a and orientation relationship. At both interfaces, misfit dislocations formed to compensate the lattice mismatch as found by high-resolution transmission electron microscopy (HRTEM). Electron energy-loss near edge structure (ELNES) studies revealed that the interface is terminating with an Al layer resulting in Al–Nb bonds. Identical sandwiches were investigated on the meso- and macroscopic scale by performing compression tests and simultaneously monitoring the strain development at (001)_Nb and crystal faces. The full-field optical strain measurements (FFOM) revealed that the strain is localized at the interfaces when observed at the (001)_Nb face while it is along the maximum shear directions of 36–54° inclined to the interface when observed at the face. The strain localization along a specific maximum shear direction results in the cleavage of Al₂O₃, always initiating from the interface possessing the and orientation relationship.     

Synthesis, Characterization, and Thermochemical Study on a Ternary Complex [Sm(m-MOBA)3phen]2

A new ternary solid complex of samarium chloride hexahydrate with m-methoxybenzoic acid and 1,10-phenanthroline, [Sm(m-MOBA)₃phen]₂ (m-MOBA: m-methoxybenzoic; phen: 1,10-phenanthroline), was synthesized and characterized by elemental analysis, IR spectra, UV spectra, molar conductance, and thermogravimetric analysis. The dissolution enthalpies of SmCl₃·6H₂O (s), m-HMOBA(s), phen·H₂O (s), and [Sm(m-MOBA)₃phen]₂(s) in the calorimetric solvent (V_DMF:V_CYC:V_HCl = 2:1:2) were determined by an advanced solution-reaction isoperibol calorimeter at 298.15 K, respectively. The standard molar enthalpy of reaction was determined to be D_r H_m^q = (233.97 ±1.15) kJ · mol^-1{\Delta_{\rm r} H_{\rm m}^\theta =(233.97 \pm 1.15)\,{\rm kJ}\,{\cdot}\,{\rm mol}^{-1}}. In accordance with Hess’ law, the standard molar enthalpy of formation of the title complex [Sm(m-MOBA)₃phen]₂(s) was estimated to be −(5054.6 ± 9.5) kJ · mol⁻¹.     

Luminescence and EPR studies of Y2O3:Gd3+ phosphors prepared via solution combustion method

Gadolinium-activated Y₂O₃ phosphor has been prepared by combustion process in a short time of 5 min. The phosphors are well characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive analysis of X-ray. The as-prepared Y₂O₃:Gd powder shows that all the peaks are due to the Y₂O₃ cubic phase. Upon UV light excitation (276 nm), the phosphor exhibits a strong and sharp UV emission at 314 nm and is ascribed to ⁶ \textP _{7/ 2}  ?  ⁸ \textS _{7/ 2} ^{ 6} {\text{P}}_{ 7/ 2} \, {\to}\, ^{ 8} {\text{S}}_{ 7/ 2} transition of Gd³⁺ ions. The EPR spectrum of Y₂O₃:Gd phosphor exhibits resonance signals with effective g values at g = 1.96, g = 2.88, and g = 6.08 and are attributed to Gd³⁺ ions located at sites with weak, intermediate, and strong cubic symmetry fields, respectively. It is observed that the population of spin levels (N) and linewidth depends on temperature. The paramagnetic susceptibility (χ) is also evaluated as a function of temperature and discussed.     

The effect of growth conditions and N<Subscript>2</Subscript>/O<Subscript>2</Subscript> ambient on LO-phonon replicas during epitaxial growth of ZnO on c-sapphire

High quality heteroepitaxial thin films of ZnO:N were grown by pulsed laser deposition using a two-step growth method and annealed in situ at different temperatures and ambient conditions. Films were analyzed by X-ray diffraction (XRD), electrical measurements, and photoluminescence experiments at low temperatures to investigate the effect of nitrogen doping. The XRD results demonstrate epitaxial growth on the c-sapphire substrates, with average grain size of 57 nm. Photoluminescence spectra reveals a peak at 3.061 eV (405.1 nm) which is part of the longitudinal-optical-phonon replicas of excitons bound to neutral acceptors \textA₁⁰  \textX_\textA {\text{A}}_{1}^{0} \,{\text{X}}_{\text{A}} at 3.348 eV (370.4 nm), attributed in recent investigations to a newly reported donor–acceptor pair. Electrical resistivity and Hall effect measurements were performed using standard four point van der Pauw geometry at room temperature. Fresh films exhibited a resistivity of 3.1 × 10⁻³ Ω cm, a carrier density of 1.3 × 10¹⁹ cm⁻³, and a mobility of 53 cm²/V s. During approximately 2 weeks the as-deposited films presented a p-type behavior, as shown by the positive sign of the Hall constant measured. Thereafter, films reverted to n-type. From electrical measurements and photoluminescence spectra, the acceptor energy was determined to be 150 meV, in close agreement with reported values. These results are consistent with those presented in the literature for high purity crystals or homoepitaxial thin films, even though samples for the present study were processed at lower annealing temperature.     

Effect of defect dipoles on the dielectric and electrical properties of Mn:K2Ti6O13 lead-free ceramics: EPR spectroscopy-cum-dielectric-spectroscopy

In this paper, we report the synthesis of Mn:K₂Ti₆O₁₃ lead-free ceramics in a monoclinic phase with microtubular surface morphology via high temperature solid-state reactions. EPR-spectroscopy, achieved at room temperature and at X-band frequencies, recognised Mn²⁺, Mn³⁺, and Mn⁴⁺ partial substitutions at Ti⁴⁺ lattice sites with dominating Mn²⁺ substitution, and identified ( \textFe_\textTi^￠ {\text{Fe}}_{\text{Ti}}^{\prime } – V_\textO ^·· V_{\text{O}}^{ \cdot \cdot } ) and ( \textMn_\textTi^￠￠ {\text{Mn}}_{\text{Ti}}^{\prime \prime } – V_\textO ^·· V_{\text{O}}^{ \cdot \cdot } ) defect associate dipoles exhibited in the low-field EPR signals which smeared with excessive doping due to augmented exchange interactions. These dipoles rendered diffusive nature to the ferroelectric-paraelectric type phase transitions recognized in the ε _r (T) plots. Space charges, dipole orientation, and electrical conduction cooperatively contributed to dielectric losses. The study also provides a select composition with x = 0.05 mol% doping, performing low loss with high dielectric permittivity useful for high-temperature applications. Conductivity data proposed a shift from electronic (hopping) conduction mechanism in the low-temperate region to ionic (intratunnel) conduction at high-temperatures. Whereas slight doping augmented a.c. conductivity due to increased spin-phonon interaction and commanding electron hopping conduction, heavy doping reduced it, attributed to shrinkage of tunnel space and trapping of conduction electrons.