Effect of Sr content on structure and electrical properties of La1−x Sr x MnO3 from ITSOFC cathode view point

The samples belonging to La_1−x Sr _x MnO₃ series, prepared by combustion route without using fuel, exhibit crystal structural phase transition with the change in Sr content. Less than 40 mol% Sr is partially substituted in the crystal structure of LaMnO₃. The structural phase transition from rhombohedral to cubic, cubic to tetragonal, and tetragonal to orthorhombic takes place on 40, 60, and 80 mol% addition of Sr. The highest electrical conductivity in La_0.4Sr_0.6MnO₃ is understood to be due to the maximum concentration of polaron. The polarons are formed due to the conversion of Mn³⁺ to Mn⁴⁺ so as to achieve electroneutrality after substitution of Sr²⁺ for La³⁺.     

Early-stage ordering in in-situ annealed Fe51Pt49 films

We evidenced an early-stage ordering (ESO) in Fe₅₁Pt₄₉ film before the appearance of superlattice diffraction (long-range-order, LRO) using 40-nm-thick films prepared by magnetron sputtering onto quartz substrate. The appearance of L1₀ phase for samples deposited at substrate temperatures (T_s) 400 °C and higher was verified by X-ray diffraction. Surface roughness of Fe₅₁Pt₄₉ films, obtained via X-ray specular reflectivity with computational fitting, increases from 3.8 to 11 Å as T_s is increased from 25 to 275 °C. As further increase of T_s to 375 °C, the roughness drops to 3.2 Å and then increases again to 38 Å with T_s up to 700 °C. Measurement on residual strain demonstrates that it is initially compressive at T_s<400 °C. Thereafter the strain transfers to a tensile one and increases in magnitude as increasing T_s up to 700 °C corresponding to LRO transformation. Local atomic rearrangement is observed for samples deposited at T_s>250 °C by using extended X-ray absorption fine structure. Coercivity of films increases from 10 to 460 Oe as T_s increase from 25 to 375 °C (ESO) and then from 460 to 10,700 Oe with T_s 375-700 °C (normal LRO). The worked out quantitative estimation of ESO engages with that of LRO before T_s 400 °C.     

<Emphasis Type="Italic">ρN</Emphasis>-resonance dynamics in the proton nucleus reaction

The strong coupling of rho meson to the nucleon produces s- and p-wave rho-meson-nucleon (ρN) resonances. In a nucleus, the ρN-resonance-hole polarization generates the optical potential or self-energy for the ρ meson. The scattering of ρ meson due to this potential provides valuable information about the ρN-resonance dynamics in a nucleus. To investigate it, we use this potential to calculate the mass distribution spectrumfor the ρ meson produced coherently in the proton-nucleus reaction. The cross sections arising due to s- and ρ-wave ρN resonances have been presented. The coherent and incoherent contributions to the cross sections due to these resonances are compared. In addition, the calculated results due to nonrelativistic and relativistic ρ-meson self-energy are illustrated.     

Structural and electrical transport properties of FeH x under high pressures and low temperatures

We present the first successful in situ simultaneous measurement of the electrical resistance and X-ray diffraction of FeH _x (x～ 1) under high-pressure H₂ up to 25.5 GPa and low temperatures down to 9 K. The electrical resistivity ρ showed a sharp increase with the formation of iron-hydride FeH _x (x～ 1) at 3.5 GPa. The ?′-phase of FeH _x was found to be metallic up to 25.5 GPa. The ρ vs. T curves up to 16.5 GPa approximately follow Fermi-liquid law below 25 K. However, T ⁵ was found to be better fitting at 25.5 GPa. This change can be considered to be related to the previously reported ferromagnetism collapse at corresponding pressure.     

Van der Pauw resistivity measurements on evaporated thin films of cadmium arsenide, Cd3As2

Cadmium arsenide is a II-V semiconductor, exhibiting n-type intrinsic conductivity with high mobility and narrow bandgap. It is deposited by thermal evaporation, and has shown the Schottky and Poole-Frenkel effects at high electric fields, but requires further electrical characterisation. This has now been extended to low-field van der Pauw lateral resistivity measurements on films of thickness up to 1.5 μm. Resistivity was observed to decrease with increasing film thickness up to 0.5 μm from about 3 × 10⁻³ Ω m to 10⁻⁵ Ω m, where the crystalline granular size increases with film thickness. This decrease in resistivity was attributed to a decrease in grain boundary scattering and increased mobility. Substrate temperature during deposition also influenced the resistivity, which decreased from around 10⁻⁴ Ω m to (10⁻⁵ to 10⁻⁶) Ω m for an increase in substrate deposition temperature from 300 K to 423 K. This behaviour appears to result from varying grain sizes and ratios of crystalline to amorphous material. Resistivity decreased with deposition rate, reaching a minimum value at about 1.5 nm s⁻¹, before slowly increasing again at higher rates. It was concluded that this resulted from a dependence of the film stoichiometry on deposition rate. The dependence of resistivity on temperature indicates that intercrystalline barriers dominate the conductivity at higher temperatures, with a hopping conduction process at low temperatures.     

Charm production in 400 GeV/c proton-emulsion interactions: Bombay-Chandigarh-Delhi-Jammu Collaboration

5032 proton-emulsion interactions at 400 GeV/c momentum have been carefully scrutinized for production and decay of charged charm particles. In order to detect these decays, shower tracks from 3056 stars have been followed to a maximum length of 1 mm and those from 1976 stars up to 2 mm. A total of 23 three-prong charm-like candidates have been recorded in the forward cone. The background due to γ-overlap on a shower track, trident/pseudo-trident production and secondary interactions is estimated to be 15. Attributing the signal of 8 events to Λ_c⁺ and assuming the branching ratio of Λ_c⁺ → 3 prong to be 0.6 and τ_Λc to be 10^?13 sec we obtain the production cross section to be 106±39μb/nucleon. Out of these 8 events one example of semileptonic decay of Λ_c⁺ is seen.     

<Superscript>210</Superscript>Pb and <Superscript>210</Superscript>Po levels in sediments,water, and bioindicators in the Cananeia-Iguape estuary-Sao Paulo-Brazil

The purpose of this work was to determine levels of ²¹⁰Pb and ²¹⁰Po in seawater, sediment cores, fish and seafood as well as to estimate the concentration factors and the bioindicators for ²¹⁰Pb and ²¹⁰Po in marine organisms collected in the estuary. ²¹⁰Pb levels in seawater varied from 2.1 to 6.2 mBq.L^?1 and for ²¹⁰Po ranged from 1.6 to 4.1 mBq.L^?1. ²¹⁰Pb concentration factors in fish varied from 0.5×10² to 0.8×10³, in crustaceans from 0.5×10³ to 0.2×10⁴ and in shellfish from 0.2×10⁴ to 0.3×10⁴. ²¹⁰Po concentration factors in fish varied from 0.9×10² to 0.5×10⁴, in crustaceans from 0.5×10⁴ to 0.2×10⁵ and in shellfish from 0.3×10⁵ to 0.9×10⁵. The results obtained to the concentration factors indicated that shellfish and crustaceans are good bioindicators for the radionuclides studies. Some species of fish also accumulated significantly quantities of these radionuclides.     

Determination of fluorescence and non-radiative de-excitation rates of excited 3-pentanone at low pressures

3-Pentanone photophysics measurements and subsequent fluorescence quantum yield (FQY) model development are presented. A heated, flowing optical cell and laser excitation at 248, 266, 277, and 308 nm were utilized, allowing investigation of FQY and absorption cross-section values for 3-pentanone vapor from 298 to 690 K and 10 to 30 mbar. Measurements of FQY were also made for 20 mbar of 3-pentanone at 1.3 bar total pressure in nitrogen from 298 to 530 K and in air from 298 to 487 K. Absolute FQY was determined by calibration to Rayleigh scattering of nitrogen gas. Based on these FQY measurements and fluorescence lifetime data from previous work, the fluorescence rate k _f was determined to be 3.70×10⁵ s⁻¹. The current work extends knowledge of the non-radiative rate k _nr to vibrational energies of 15000 cm⁻¹, and the expression for k _nr was optimized to include a fit to these new data points. Finally, variation of FQY with 3-pentanone vapor pressure was used to optimize the vibrational relaxation cascade parameter α _3p . The updated FQY model for 3-pentanone vapor shows agreement within 8% to the current FQY data across the investigated range of temperatures and pressures.     

Neutron,x-ray and lattice dynamical studies of paraelectric Sb2S3

Neutron and x-ray diffraction studies of Sb₂S₃ indicate extensive diffuse scattering in the plane perpendicular to the chain axis of polymer-like (Sb₄S₆) _n molecules. The crystal structure of the paraelectric phase is said to be orthorhombic with space group D _2h ¹⁶ with four molecules per unit cell. The observed diffuse scattering may be due to static disorder or some dynamical effects. In this paper the authors have examined the possible dynamical origin by recourse to lattice dynamical studies. Dispersion relation of phonons along the three symmetry directionsa*,b* andc* is evaluated based on a lattice dynamical model incorporating Coulomb, covalent and a Born-Mayer-like short range interactions. Group theoretical analysis based on the group of neutral elements of crystal sites (GNES) was essential in order to examine and aid in the numerical computations. The group theoretical technique involving GNES extended to ‘pseudo-molecular’ systems is also discussed in this context. The phonon dispersion relation shows that there are rather flat TA-TO branches of very low frequency in thea andc directions which may give rise to diffuse scattering. The branches along theb-axis are quite dissimilar to those alonga andc axes because of anisotropy. Variation of the potential parameters leads to instability of the lowest TA-TO branch. This is suggestive of a temperatures or pressure-dependent phase transition. However since these modes are optically ‘silent’ one needs to carry out either high resolution neutron scattering or ultrasonic studies to confirm various aspects of the theoretical studies.     

New neutrino experiments

Following incredible recent progress in understanding neutrino oscillations, many new ambitious experiments are being planned to study neutrino properties. The most important may be to find a non-zero value of θ₁₃. The most promising way to do this appears to be to measurev _μ →v _e oscillations with anE/L near Δm _atmo ² . Future neutrino experiments are great.     

Multipole moments and spin-dependent sum rules and their applications to f72 and s-d shell nuclei

Matrix elements of multipole operators, defined separately for neutrons and protons, are related to spin-dependent sums of spectroscopic factors. A clarification of their relation to the matrix elements of single-particle operators enables the overlap representation to be formally extended to a stripping form for J ≠ 0 operators. Multipole moments obtained from $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ transfer data are found to be dominated by the quadrupole moments when the final nucleus is odd-odd.A previously found (2J + 1) rule for spectroscopic sums, which arises when the odd-J multipole moments vanish, is shown to lead to approximate sum rules which apply separately to stripping and pickup data. The sum rules are generally well satisfied for transfers leading to odd-odd nuclei in the s-d shell.     

Response of fcc metals and L12 and D022 type trialuminides to uniaxial loading along [100] and [001]: ab initio DFT calculations

Ab initio density-functional calculations have been used to investigate the response of the face-centred cubic (fcc) metals Al and Cu, and of the L1₂- and D0₂₂-type trialuminides Al₃(Sc,Ti,V) to uniaxial loading along the [100] and [001] directions. The results obtained under uniaxial strains are compared to the response to biaxial (epitaxial) strains. The ideal tensile and compressive strengths and their limitation by shear instabilities along these deformation paths have been calculated. Although the response of both pure fcc metals could be expected to be very similar, our results show a fundamental difference: whereas for Cu a special invariant state with C ₂₂?=?C ₂₃, leading to a bifurcation from the tetragonal to an orthorhombic deformation path, is reached at a strain of 10%, for Al this state is reached only at a strain of 33% close to the critical strain defining the ideal tensile strength. The reaction of the L1₂-type trialuminides is comparable to the response of Al; no bifurcation to an orthorhombic deformation path is predicted. The response of the D0₂₂-type trialuminides is different from that of the L1₂-type phases because of the difference in the stacking of the atomic planes along the [001] direction. For D0₂₂-type trialuminides, the uniaxial compression along this direction or epitaxial tension in the (001) plane leads to the formation of a stress-free D0₃ structure, in complete analogy to the fcc???bcc transformations observed for the pure metals. Under uniaxial [100] loading the guiding symmetry along the deformation path is orthorhombic and leads to the formation of special structures under both tension and compression parts, which are related to the D0₃ structure in the same way as the parent D0₂₂-lattice is related to the L1₂ structure.     

Sensor Properties of Nanostructured Systems Based on Indium Oxide with Co<Subscript>3</Subscript>O<Subscript>4</Subscript> or ZrO<Subscript>2</Subscript> Additives

The effect of Co₃O₄ and ZrO₂ additives on the sensory response of In₂O₃-based nanostructured composites to H₂ and CO is studied. It is shown that the addition of small amounts of Co₃O₄ or ZrO₂ to In₂O₃ leads to a sharp increase in the sensory response to hydrogen. The maximum sensory response of the ZrO₂?In₂O₃ composite to 1100 ppm of hydrogen increases from 80 to 270 as the ZrO₂ content changes 0 to 20 wt %. The response to CO varies only slightly. For Co₃O₄?In₂O₃ composites, the maximum response to H₂ and CO increases with the Co₃O₄ content within 0?10 wt %. A further increase in the Co₃O₄ content leads to a significant decrease in the response, with composites containing ～60 wt % Co₃O₄ being characterized by a very low efficiency. In the Co₃O₄?In₂O₃ system with a content of up to 60 wt % Co₃O₄, electronic conduction is realized, which changes to hole conduction at Co₃O₄ within 80?100 wt %. In the ZrO₂?In₂O₃ system, electric current flows through In₂O₃ nanocrystals, i.e., n-type conduction takes place. Possible reasons for the observed effects are discussed.     

Determination of intrinsic FMR line broadening in ferromagnetic (Fe44Co56)77Hf12N11 nanocomposite films

Ferromagnetic nanocomposite (Fe₄₄Co₅₆)₇₇Hf₁₂N₁₁ films were deposited to investigate their intrinsic damping mechanisms due to scattering of itinerant electrons, which carry the magnetic moment of the ferromagnetic transition elements. The films were produced by reactive r.f. magnetron sputtering using a 6 in. Fe₃₇Co₄₆Hf₁₇ target. They were annealed at 400 °C in a static magnetic field, in order to induce in-plane uniaxial anisotropy. Subsequently, the films can be considered as uniformly magnetised. A ferromagnetic resonance frequency (FMR) of around 2.3 GHz could be attained, which was determined by measuring the real and imaginary parts of the frequency dependent permeability up to 5 GHz. The imaginary part, which represents a typical resonance curve, was utilised to obtain its full-width at half-maximum Δf_eff (FWHM) for the total damping behaviour characterisation. Thereby, it is possible to extract the intrinsic Gilbert damping parameter α_int, which in turn can be decomposed into two additional damping terms α_sf and α_os allocated to “spin-flip” and “ordinary scattering”, respectively. This result is correlated and discussed in terms of a verified theoretic model, to identify whether damping due to spin-flip scattering and/or ordinary scattering is dominant.     

Vortex dynamics in single crystal Hg-1201

Anisotropic superconducting materials often show an enhanced pinning along their crystallographic ab-planes. To obtain information about such a behavior of the high-T_c system Hg-1201 (HgBa₂CuO₄) magnetic investigations on a single crystal are performed for the two field orientations, parallel to the c-axis and parallel to the ab-planes. The dependence of the ac magnetization on temperature, magnetic field and frequency is determined. Compared to former results on powder samples of this system no indication of a second peak in the imaginary part of the susceptibility χ′′ is found. It seems to be shifted to higher temperatures overlapping now with the first peak. The corresponding irreversibility lines for both orientations, parallel to c and parallel to ab, are determined and discussed within the framework of a “diffusion” model.     

Magnetic characteristics of R6Mn23 hydrides (R = Gd,Ho or Er)

R₆Mn₂₃ systems, with R = Gd, Ho and Er, were hydrided to the composition R₆Mn₂₃H_x where x ap; 22. Magnetic properties of these systems and the parent intermetallics were studied over the temperature range 4 to 300 K and at applied field up to 21 kOe. Since Y₆Mn₂₃H₂₅ was established earlier to exhibit only Pauli paramagnetism, the magnetism of the R₆Mn₂₃ hydrides must originate with the rare earth sublattice. Gd₆Mn₂₃H₂₂ orders at ≈ 150 K, whereas ordering in Gd₆Mn₂₃ occurs at 468 K. The moment measured at 4 K indicates a non-collinear structure, perhaps generated by competition involving exchange between nearest and next nearest neighbors. The hydrides involving Ho and Er appear to remain paramagnetic to the lowest temperatures studied, perhaps because the reduced de Gennes factor exchange is insufficient to produce magnetic ordering. The possibility cannot be excluded, however, that they are antiferromagnetic.     

Tunable diode laser spectroscopy of benzene near 1684 nm with a low-temperature VCSEL

We describe the application of a long-wavelength vertical-cavity surface-emitting laser (VCSEL) with extended tuning range to the detection of benzene vapor at atmospheric pressure. A benzene absorption feature centered at 1684.24 nm was accessed by reducing the heat sink temperature of a VCSEL designed for room-temperature operation to −55°C. This allowed us to increase the injection current and thus to extend a single-scan tuning interval up to 46.4 cm⁻¹ or 13.2 nm around a central wavelength of 1687.4 nm. Five absorption lines of methane in the 5903–5950 cm⁻¹ range could be acquired within single laser scans at a repetition rate of 500 Hz. A benzene absorption feature between 5926 and 5948 cm⁻¹ was recorded for concentration measurements at atmospheric pressure using a single-pass 1.2 m absorption cell. A 50 ppmv mixture of CH₄ in N₂ was introduced into the cell along with benzene vapor to calibrate benzene concentration measurements. Benzene mixing ratios down to ∼90 ppmv were measured using a direct absorption technique. The minimum detectable absorbance and detection limit of benzene were estimated to be ∼10⁻⁴ and 30 ppmv, respectively. Using the wavelength modulation technique, we measured a second harmonic sensor response to benzene vapor absorption in air at atmospheric pressure as a function of modulation index. We conclude that a low-temperature monolithic VCSEL operating near 1684 nm can be employed in compact benzene sensors with a detection limit in the sub-ppm range.     

Probing anomalous Higgs couplings at an <Emphasis Type="Italic">eγ</Emphasis> collider using unpolarised beams

We examine the sensitivity of eγ colliders (based on e ⁺ e ⁻ linear colliders of c.m. energy 500 GeV) to the anomalous couplings of the Higgs to W-boson via the process e ⁻ γ → νWH. This has the advantage over e ⁺ e ⁻ collider in being able to dissociate WWH vertex from ZZH. We are able to construct several dynamical variables which may be used to constrain the various couplings in the WWH vertex.      

Γ(Z → b ): A signature of hard mass terms for a heavy top

We calculate analytically the weak radiative corrections to the weak neutral current gauge boson-bottom fermion vertex, keeping the mass m_t of the internal fermion line for the relevant diagrams. We find, to order α, a hard mass-term dependence m_t²/M_W² of the amplitude, for large m_t values. Its origin comes from the unphysical charged Higgs coupling to fermions in the renormalizable gauge or, equivalently, from the longitudinal charged gauge boson couplings. The diagonal Z⁰ decay width to b-quarks decreases, due to these weak radiative corrections, by 0.6%–2.5% when the top mass m_t varies from 45 to 200 GeV.     

Diffusion et rotation du fluor dans un fluorure ionique: etude par R.M.N. de Ba4−xZr2 + x2F16

Fluoride subcell thermal behavior has been studied from 180 to 450 K for two compositions Ba_4?xZr_{2 + $\text{x}\text{2}$}F₁₆ corresponding to x = 0.04 and x = 0.26. At low temperature two fluorine atoms rotate quickly around a baryum atom. Above 330 K this phenomenon leads diffusion thanks to an exchange mechanism between the previous fluorine atoms and the others, the whole anipnic subcell being then affected by the fluorine mobility. Activation energy decreases from 0.52 to 0.46 eV as x increases from 0.04 to 0.22. This property seems to be closely related to the formation of cationic vacancies whose number increases with x.