Diffusion of indium into cadmium sulphide

The diffusion of In into CdS was studied using optical, microprobe and radiotracer methods over a temperature range from 729 to 1411 K. When diffusion occurred with a large excess of In metal, the diffusion coefficient was found to be linearly proportional to In concentration in the CdS and a sharp, optically observable diffusion front existed. Varying the Cd/In atomic ratio in the metal produced a transition to normal, concentration independent diffusion for Cd/In ratios greater than unity. The diffusion is markedly anisotropic, with fast diffusion perpendicular to the crystal c-direction. Very high values were measured for the diffusion coefficient in the concentration dependent regime (up to 2 × 10^?11m²s^?1) and the mobile specie is thought to be the (InV) complex. The total apparent activation energy was found to be 2.03 and 2.30 eV (perpendicular and parallel to the c-direction respectively) and the anisotropy of the activation energy measured directly was 0.250 eV. On converting the concentration dependent diffusion coefficients to a standard concentration a straight line Arrhenius plot was obtained below 1200 K, which gave an activation energy for defect motion of 1.56 ± 0.12eV perpendicular to the c-direction and 1.81 ± 0.12 eV parallel to the c-direction.     

Concentration dependence of the critical resolved shear stress of cadmium-silver alloy single crystals at low temperatures

The increase of the critical resolved shear stress of cadmium single crystals by addition of silver has been investigated in the temperature range of 77 K to 199 K. At all temperatures the critical resolved shear stress increases withc ^2/3, wherec is the atomic concentration of silver as solute, and it decreases with increasing temperature. The concentration dependence of the critical resolved shear stress is explained according to the theory ofLabusch (phys. stat. sol.41 (1970), 659).     

Electrical conductivity of biphasic mixtures of molten silver iodide and lithium fluoride,chloride, and bromide

The electrical conductivity (EC) method was used for the biphasic systems of AgI with LiF, LiCl, or LiBr. The difference between the magnitudes of the conductivities for the equilibrium phases of the LiCl+AgI and LiBr+AgI melts decreases with an increase in temperature, becoming zero at 1250 and 983 K. For these temperatures, the values of critical conductivity are κ _c  = 4.70 S cm^?1 and κ _c  = 3.90 S cm^?1, respectively. The melt containing lithium fluoride exists in two phases up to a temperature of 1245 K. The temperature dependence of the differences between the conductivities for the coexisting phases is described as an exponential equation, with the critical exponent 0.89. This value is 11% less than that found for alkali halide melts. The covalent bonding between the silver and halide ions can be understood as causing the difference between the critical exponents of the alkali halide melts and those of silver iodide-containing mixtures.     

Conductivity enhancement in fluorite-structured Ba1−xLaxF2+x solid solutions

The ionic conductivity of single crystals of the fluorite-structured solid solutions Ba_1?xLa_xF_2+x(10^?3 <×<0.45) has been studied as a function of temperature and composition in the range 300–900 K. Three regions can be discerned in the concentration dependence of the ionic conductivity: a dilute concentration region (x<10^?3), where classic relations between solute content and ionic conductivity hold; an intermediate concentration region (10^?3<x?5×10^?2), where large changes occur in the conductivity activation enthalpy and the magnitude of the conductivity; and a concentrated solid solution region (x?5×10^?2) characterized by enhanced ionic motion. In the dilute region the migration enthalpy for interstitial fluoride ions is determined to be 0.714 eV, while a value of 0.39 eV is found for the (La_BaF_i)^X association enthalpy. The defect chemistry in the intermediate concentration region is shown to be controlled by a superlinear increase of the concentration of mobile defects, while in the concentrated solid solution region a composition-independent amount of ≈1 mole% of interstitial fluoride ions with enhanced mobility, carry the current.     

Thermal conductivity of gold and silver at high pressures

The thermal diffusivities of gold and silver have been measured under pressure up to 2.5 GPa at room temperature. From the measured data the pressure dependence of the thermal conductivity, λ, has been calculated. The values found for the pressure coefficient λ^?1$\text{δλ}\text{δP}$ were 3.9 × 10^?2GPa^?1 for gold and 4.0 × 10^?2 GP silver at atmospheric pressure. The results are compared to theoretical predictions of the pressure dependence and also to previous experimental results for copper and aluminium. For the noble metals, small angle or “vertical” scattering of electrons is shown to have a stronger volume dependence than “horizontal” scattering.     

Diffusion of titanium in slightly reduced rutile

The self-diffusion of ⁴⁴Ti in slightly reduced rutile. TiO_2?δ, was measured along the c axis over the temperature range of 1000–1100°C between 0.2 and 1 × 10^?18atm. oxygen pressure. These measurements enabled the determination of the defect structure of TiO_2-δ for 0.02 ?gd ? 0.001. For oxygen pressures between 1 × 10^?13 and 1 × 10^?16atm. at 1058.4°C random tetravalent titanium atoms are the predominant defects evident from self-diffusion. The enthalpy of motion was determined as ΔH_m = 57.03 ± 4.9% kcal/mole. From the activation energy at 1.69 × 10^?16atm., the enthalpy of formation for tetravalent titanium interstitials was determined as ΔH_f = 276 ± 15.6% kcal/mole.For oxygen pressures less than 1 × 10^?16atm. at 1058.4°C, the tracer diffusion coefficient shows a continuous decline as the oxygen pressure is lowered. Comparisons with thermogravimetric studies and consideration of the similarity in structure between nonstoichiometric point defect phases and the first homologous series phase indicate that the order-disorder transition retains a considerable degree of short range order below the critical concentration in the form of Wadsley defects.     

A search for rare types of fission induced in silver and bromine nuclei

Ternary and quaternary fission produced in silver and bromine nuclei have been studied withK5 nuclear emulsion exposed to 1.8 GeV/cK ⁻ beams. The frequency of the ternary events is found to be ∼0.08 of that of the binary events produced in the same volume of the emulsion. The range ratio and range distribution of the fission fragments are studied and the angles between each pair of the fragments are determined. Ranges are found to vary from 5 to 40μ with a maximum number lying between 5 and 10μ. The angles between the fission fragments are found to form a broad distribution extending from 40° to 180°. A few of the events have also been analysed to give them a possible identity. A possible case of quaternary fission has also been reported. This paper was presented at the Symposium on 3rd High Energy Physics held at Bhubaneswar during November 1976.     

M-Zentrenbildung in röntgenbestrahlten KCl-Kristallen

The production of F- and M-centres in KCl by X-irradiation has been studied at temperatures between ?20 °C and 50 °C. The optical absorption measurements could be conducted without interrupting the X-irradiation. The results can be summarized as follows: 1. In Harshaw KCl crystals the number of F-centres created by the so-called fast coloration process was proportional to the height of the absorption band at 204 mμ prior to the irradiation. 2. The F-centres formed by the fast process did not contribute to the formation of M-centres. 3. In crystals with a strong absorption band at 204 mμ unstable M-centres were observed, which decayed rapidly after the cessation of the X-irradiation. Their concentration was found to be independent of the F-centre concentration. 4. At temperatures below 0 °C the relation between the concentration of the stable M-centres and the F-centre concentration could not any longer be represented by [M]=k ₁₂·[F₁]·[F₂]+k ₂₂·[F₂]², F₁ and F₂ referring to the F-centres created respectively by the fast and the slow coloration process. Except at very low F₂-centre concentrations however the relationship [M]=k ₀+k ₂·[F₂]² represented the experimental data at all temperatures between ?20 °C and 50 °C. At constant temperaturek ₂ varied withL, the X-ray energy absorbed per unit time and unit volume, according to 1/k ₂=a+bL+cL ². The temperature dependence ofa ^?1 b ^?1 andc ^?1 could be approximated by Boltzmann factors. The corresponding activation energies wereE _a=0.12 eV,E _b=0.53 eV,E _c=0.97 eV.     

Giant optical nonlinearity of silver-doped silicon thin film at low power input: laser-triggered cluster resonance

Silver-doped silicon thin films were deposited on glass substrate in a co-sputtering procedure. Silver nanoparticles were segregatedly distributed. The nonlinear properties were extracted by z-scan measurements at low laser input power. For about 50% silver density, the nonlinear absorption and refraction coefficients peaked, respectively, at ?8.086×10^?2?m/W and 1.47×10^?9?m²/W, which, with respect to the input intensity, are several orders higher than reported data. The sudden surge of nonlinear responses was explained satisfactorily based on a self-consistent microscopic model calculation for silver clusters. Resonances exist and depend apparently on the laser-modified local cluster concentration.     

Pair production of pions with symmetric momenta in the range 0.5⩽pT⩽2.0 GeV/c In 70 GeV p-p collisions

The invariant cross-section slope of the pp→π⁺π^?+X process as a function of p_T is found to have a break near 1 GeV/c. Fitting the cross section by a sum of two exponents gives the values of powers (12.3±0.9)(GeV/c)^?1 and (8.7±0.6)(GeV/c)^?1. The experimental points at p_T?1 GeV/c are significantly higher than predictions based on hard scattering models such as QCD and CIM.     

A Validated Spectrofluorimetric Method for the Determination of Citalopram in Bulk and Pharmaceutical Preparations Based on the Measurement of the Silver Nanoparticles-Enhanced Fluorescence of Citalopram/Terbium Complexes

A simple, sensitive, and accurate spectrofluorimetric method was developed for the determination of citalopram in bulk and pharmaceutical preparations. The method is based on the enhancement of the weak fluorescence signal (FL) of the Tb (III)-citalopram system in the presence of silver nanoparticles. Fluorescence intensities were measured at 555 nm after excitation at 281 nm. Prepared silver nanoparticles (AgNPs) were characterized by UV-Visible spectra and transmission electron microscopy (TEM). Various factors affecting the formation of citalopram-Tb (III)-AgNPs complexes were studied and optimized. The fluorescence intensity versus concentration plot was linear over the range 0.02–14 μg?mL^?1, with an excellent correlation coefficient of 0.9978. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 7.15?×?10^?6?μg?mL^?1 and 2.38?×?10^?5?μg?mL^?1 respectively. The proposed method was found to have good reproducibility with a relative standard deviation of 3.66 % (n?=?6). The interference effects of common excipients found in pharmaceutical preparations were studied. The developed method was validated statistically by performing recoveries studies and successfully applied for the assay of citalopram in bulk powder and pharmaceutical preparations. Percent recoveries were found to range from 98.98 % to 100.97 % for bulk powder and from 96.57 % to 101.77 % for pharmaceutical preparations.     

Interactions of point defects with dislocations in silver chloride crystals

Internal friction techniques at 35 kHz were used to study the interactions between point defects and dislocations in crystals of silver chloride. The Granato-Lücke plots of the amplitude-dependent decrement were not linear, but were concave upward. Various analyses of these data all gave pin-dislocation binding energies of approximately 0·2 eV. An extensive study was made of the decay of the amplitude-independent decrement after “excitation” by high-amplitude oscillation; the Granato-Lücke L⁴ law was found valid, but the arrival of pins proceeded as t^1/3, rather than the usual t^2/3 found in deformed specimens. A first-order model of the response of a slightly perturbed Maxwell atmosphere about the dislocation is presented. The model quantitatively describes the experimental results. The activation energy of the rate constant was found to be 0·42 eV, consistent with data on solute diffusion and strain-aging.     

Coercivity of single-domain nickel wires

The coercivity H_c of compacts of thin (0.1?5 μ diameter) nickel wires embedded in a silver matrix has been measured as a function of the effective wire radius d_eff. H_c increases linearly with 1/d_eff², in agreement with Aharoni's theory of magnetization reversal by curling. From the slope, δH_{c/gd (deff^?2)}, upper and lower bounds for the exchange constant A of Nickel have been derived (77K): 1.5 × 10^?11 Wsec/m ? 3.0 × 10^?11 Wsec/m.     

Ultrasonic preparation of tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotubes for trace Ni(II) sensing

Under an aid of ultrasonic, tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotubes were prepared for Ni(II) sensing in aqueous solution. The processes involved the fabrication of tetraoxalyl ethylenediamine melamine resin by one pot way, the coating of tetraoxalyl ethylenediamine melamine resin at multiwalled carbon nanotubes (MWCNTs), and the determination of Ni(II). The present materials were carefully examined by Fourier transform infrared spectroscopy, field emission scanning electron microscope, and electrochemistry techniques. A great deal of amorphous microsphere could be observed for tetraoxalyl ethylenediamine melamine resin with an average diameter of 1.2 μm, and MTE could evenly adhere at the surface of MWCNTs by the ultrasonic. Tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotube-modified paraffin-impregnated graphite electrode was successfully used for the determination of Ni(II) by differential pulse adsorptive anodic stripping voltammetry. The current responses (?0.3 V) were linearly increased depending on the concentration from 1?×?10^?11 to 3?×?10^?10 M (i (μA)?=?11.1?+?7.9 c (1?×?10^?12 M); R?=?0.9901, 3σ?=?7?×?10^?12 M).     

The effect of mechanical relaxation on ultra-fast charge pulses in flexible epoxy resin nanocomposites

Previously we have reported the existence of small-amplitude charge pulses in crosslinked Polyethylene (XLPE) and epoxy resin with a mobility several orders of magnitude higher than that found for the incoherent charge transport relevant to the steady state current. Here the relationship of this phenomenon to mechanical relaxation in the material is investigated by using a series of epoxy resin nanocomposites based on a resin that has its flexibility increased above that of the fully cured glassy epoxy network by the addition of a suitable flexibilizing chemical. Differential Scanning Calorimetry (DSC) measurements show that the stiffness of the nanocomposite is progressively increased as the nanoparticle concentration increases. Pulsed Electro-Acoustic (PEA) measurements reveal that both positive and negative fast charge pulses exist in the unfilled epoxy at 45 and 70°C under a field of 10?kV/mm with mobility 5×10^?10 to 9×10^?10 m²?V^?1?s^?1, amplitude between 2×10^?5 and 3.6×10^?5 C?m^?2 and repetition rates between 8 and 12?s^?1. These values are reduced progressively as the nanoparticle concentration is increased from 0% in the unfilled epoxy. A???-mode mechanical relaxation is identified in the loss modulus by Dynamical Mechanical Analysis (DMA), whose activation energy moves to higher values with increasing nanoparticle concentration. It is shown that the repetition rates of both positive and negative pulses have similar values and are correlated with the ??-mode activation energy; a similar correlation is found for the activation energy of the mobility of positive pulses. The correlation of the activation energy of the mobility of negative pulses and that of the ??-mode is weaker although both show a progressive increase with nanoparticle concentration. The modification of the fast charge pulse properties by the mechanical stiffness of the epoxy nanocomposite is discussed in terms of the theory presented previously for their formation and transport.     

The influence of AlN interlayers on the microstructural and electrical properties of p-type AlGaN/GaN superlattices grown on GaN/sapphire templates

AlN with different thicknesses were grown as interlayers (ILs) between GaN and p-type Al_0.15Ga_0.85N/GaN superlattices (SLs) by metal organic vapor phase epitaxy (MOVPE). It was found that the edge-type threading dislocation density (TDD) increased gradually from the minimum of 2.5×10⁹?cm^?2 without AlN IL to the maximum of 1×10¹⁰?cm^?2 at an AlN thickness of 20 nm, while the screw-type TDD remained almost unchanged due to the interface-related TD suppression and regeneration mechanism. We obtained that the edge-type dislocations acted as acceptors in p-type Al _x Ga_1?x N/GaN SLs, through the comparison of the edge-type TDD and hole concentration with different thicknesses of AlN IL. The Mg activation energy was significantly decreased from 153 to 70?meV with a?10-nm AlN IL, which was attributed to the strain modulation between AlGaN barrier and GaN well. The large activation efficiency, together with the TDs, led to the enhanced hole concentration. The variation trend of Hall mobility was also observed, which originated from the scattering at TDs.     

Analysis of temperature and concentration dependence of flow stress in KCl–KBr single crystals with special reference to solute distribution

Available data on the temperature and concentration dependence of critical resolved shear stress (CRSS) of KCl–KBr solid-solution crystals containing 9, 17, 27 and 45?mol% KBr in the temperature range 77–230?K have been analyzed within the framework of the kink-pair nucleation model of plastic flow in solid- solution crystals. It is found that CRSS τ decreases with increasing temperature T in accordance with the model relation lnτ?=?A???BT, where A and B are positive constants. The CRSS τ at a given temperature depends on solute concentration c as τ?∝?c^p , where exponent p has a value between 0.33 and 0.57 as temperature T rises from 0 to 230?K. The model parameter W _o, i.e. binding energy between the edge-dislocation segment L _o involved in the unit activation process and the solute atoms close to it (T?→?0?K), which is inversely proportional to B, increases with solute concentration c monotonically as W _o?∝?c ^0.33 up to a critical value c _m?=?35?mol% KBr, which is in reasonable agreement with the model prediction W _o?∝?c ^0.25. However, W _o decreases with an increase in c beyond c _m, which indicates somewhat ordered distribution of solute in the host lattice of concentrated KCl–KBr solid solutions with c?>?c _m.     

Electrical contacts on organic crystals: TTF-TCNQ

Room temperature plots of the electrical potential measured on the surfaces of TTF-TCNQ crystals which carry current are presented. It is shown that silver paint contacts behave electrically as though thin resistive layers ($\text{? 20}\text{mhos}\text{mm}{}^2$ conductance) were inserted between the crystal and the current-injecting electrodes. The contact resistance is microscopically nonuniform, and can lead to erroneous results in 4-probe conductivity measurements. By measurement and calculation (using the method of image charges) it is demonstrated that measurement techniques which introduce nonuniform current densities into highly anisotropic crystals are subject to error unless the contacts are kept very small. The principal conductivities of TTF-TCNQ at room temperature were found to be: σ_b = 440 ± 15, σ_c ≈ 13, σ_a, = 1.30 ± 0.05 Ω^?1 cm^?1, independent of contact effects.     

Estimation of sound velocities from resonance measurements on tungsten carbide calibration spheres

Tungsten carbide spheres have been used as reference targets to calibrate echosounders. The target strength depends upon the longitudinal and transverse stress wave speeds, c₁ and c₂, in the sphere. These may be estimated from the resonance frequencies, which can be measured precisely given two or more resonances whose coupling characteristics are sufficiently different to provide well conditioned equations for these wave speeds. The resonance frequencies may be measured by sampling the echo amplitude or by spectrum analysis. The latter method is more accurate but requires more sophisticated equipment. The measurements have been corrected to remove the bias resulting from the finite bandwidth of the apparatus. Experimental results are given for 11 spheres 38·1 mm in diameter containing a nominal 6% of cobalt binder, procured in two batches from different production runs. Both stress wave speeds are significantly different between but not within the batches, and likewise the sphere density which indicates variation of the cobalt content. For a density of 14 900 kg m^?3 (6% cobalt) and at 11°C, c₁ and c₂ are estimated to be 6853 ± 19 and 4171 ± 7 m s^?1, respectively, within 95% confidence limits. Empirical equations are presented for the speeds as functions of density. The temperature coefficient of c₂ is estimated to be ?1·3 ± 0·6 m s^?1°C^?1. These results demonstrate the high accuracy of the resonance technique for estimating the stress wave speeds in spheres. The small differences observed between the spheres would have a negligible effect on the target strength at 38 kHz.