Light conversion in thin films of mixtures of mesotetraphenylporphyrin and yttrium vanadate crystallites doped with erbium. I. Photovoltaic properties and structure

The optical and photovoltaic properties of two-component TPP–Yt_0.95Er_0.05VO₄ films prepared by the spincoating method are for the first time studied. A 30% increase in the photovoltage (PV) of TPP: Yt_0.95Er_0.05VO₄ = 3: 2 films on silicon carbide (SiC) supports as compared to TPP one-component films is observed. In contrast, for films on tin dioxide (SnO₂) supports, the PV drops by 35–96% as the TPP content in the film decreases from 80 to 20%. The properties of the films are monitored by atomic force microscopy. The highest roughness of the films corresponds to a 40–60% TPP content.     

4- vs. 5-phenylquinolinolate aluminum (III) isomers

A method for the synthesis of 4-arylquinolinolate ligand and their Al^III complexes based on Michael reaction of 2-methoxyaniline with 1-phenylpropenones was developed. The resulting 4-aryl-8-methoxyquinoline was demethylated and converted to corresponding Al^III complexes. Photophysical properties of two 4-aryl-Alq₃ derivatives were then compared with properties of the parent Alq₃ and a 5-phenyl-Alq₃ congener. It appears that the 5-aryl derivatives show improved luminescence but also decreased physical stability. Electroluminescence of the prepared materials is presented and compared to Alq₃ and a 5-phenyl-Alq₃.     

The effect of relaxation on the symmetry of N.M.R. spectra

The effect of nuclear relaxation on the symmetry properties of N.M.R. spectra is examined in terms of the properties of the relaxation matrix elements R_ijkl . It is found that the symmetry relations R_ijkl = R_jilk = R_klij = Rlkij obtain for one or more dominant relaxation mechanisms under ‘extreme narrowing’ conditions. Further, the symmetry relation R_ijkl = R_{λi, λj, λk, λl} , where λ is a spin inversion operator, is shown to obtain for (a) only one dominant relaxation mechanism or (b) two dominant relaxation mechanisms which have the same commutation properties with λ. This latter symmetry relation does not obtain for two dominant relaxation mechanisms with the same order of spatial dependence and different commutation properties with λ. The effect of nuclear relaxation can therefore yield unsymmetrical first-order spectra; the application of this analysis to the determination of the absolute sign of the spin-spin coupling constants is proposed.     

Monocrystalline high-saturation magnetization ferrites for video recording head application: II. MnZn ferrites with large FeII contents

Monocrystalline Fe^II-rich MnZn ferrites are considered as candidate materials for video recording heads, to be used for both writing and reading when magnetic tapes of high coercivity are applied. It is examined how saturation magnetization and magnetostriction constants vary with chemical composition within relevant areas of the ternary composition diagram MnFe₂O₄-ZnFe₂O₄-Fe^IIO₄. From the results and data known for the magnetocrystalline anisotropy a composition is selected which offers a fairly good compromise between high-saturation magnetization and suitable soft magnetic properties. A study is presented of magnetic and electrical properties of monocrystals of this composition, relevant to their use as video recording head materials. The present paper is the second in a series of three dealing with Fe^II-rich ferrites for video recording head application.     

Electrical properties and cation migration in manganese ferrites I. Temperature dependences

High temperature behaviour of the electrical conductivity and the Seebeck effect in MnFe₂O₄ single crystals is studied both experimentally and theoretically. Various heat cycles in the temperature range 300–600 °C lead to marked changes in the temperature dependences of electrical properties. A two donor level model of electrical conduction is used to explain the observed behaviour. The influence of the cation migration between the tetrahedral and the octahedral sites of the spinel lattice on electrical properties of Mn ferrites is demonstrated.     

SiCN thin film prepared at room temperature by r.f. reactive sputtering

Silicon–carbon nitride (SiCN) thin films were deposited on Si substrate at room temperature by r.f. reactive sputtering. Fourier transform infrared spectroscopy (FTIR), optical absorption spectra (α(λ)) and electrical conductivity (σ) were studied for the thin films. The effect of the annealing on IR and σ was investigated at different temperatures. IR analysis indicates that Si–H, C–N, Si–C, Si–N, C–N and CN bonds are present in a-SiCN:H films. A shift of the stretching mode for Si–H bond to the high-wavenumber side is observed with increasing the nitrogen flow ratio γ_N2(=N₂/(Ar+H₂+N₂+CH₄)). The shift is from 2000 to 2190 cm⁻¹ when γ_N2=13.7%. The study shows that the film structure and optical and electrical properties are obviously modified readily by controlling the process parameters of deposition. The improvement in the film properties, e.g., good thermal stability, is explained mainly in terms of the cross-linked structure between the Si, C and N atoms.     

Mechanical properties of H. P. or H. I. P. SiC-whisker reinforced Si3N4-matrix composites

Abstract

Composites (SiCw/Si₃N₄m) were fabricated by H. P. or H. I. P. The mechanical properties of the materials (strength, toughness) show that H. I. P. is a suitable process for complex shapes.     

New approaches to the generalized WKB approximation. III

The problem of particle transmission through a one-dimensional potential barrier of arbitrary shape is considered within the new generalized WKB method, developed in [1, 2]. A number of properties of the matrix F(S, S_t), needed to solve specific quantum-mechanical problems, is indicated.     

Deformation hardening and the temperature dependence of the mechanical properties of ternary ordering alloys. Part II

Yield point, hardening factor, and elastic modulus are reported as functions of quenching and test temperatures for the alloys Ni₃(Fe + 3 at% Al), Ni₃(Fe + 3 at% Mn). A maximum is found in the mechanical properties near the critical temperature T_cr; this does not occur for alloys in the disordered state. The deformation aging under load is examined near this maximum and at 200 ° C. A range of linear hardening occurs up to e of 15–18% in ordered alloys, which is replaced by a range of decreasing hardening coefficient at higher . The results are discussed by reference to earlier ones for Ni₃Fe, Ni₃(FeCr). Ni₃(FeMo).     

Theory of tensor invariants of integrable Hamiltonian systems. I. Incompatible Poisson structures

This paper develops a new theory of tensor invariants of a completely integrable non-degenerate Hamiltonian system on a smooth manifoldM ⁿ. The central objects in this theory are supplementary invariant Poisson structuresP _c which are incompatable with the original Poisson structureP ₁ for this Hamiltonian system. A complete classification of invariant Poisson structures is derived in a neighbourhood of an invariant toroidal domain. This classification resolves the well-known Inverse Problem that was brought into prominence by Magri's 1978 paper deveoted to the theory of compatible Poisson structures. Applications connected with the KAM theory, with the Kepler problem, with the basic integrable problem of celestial mechanics, and with the harmonic oscillator are pointed out. A cohomology is defined for dynamical systems on smooth manifolds. The physically motivated concepts of dynamical compatibility and strong dynamical compatibility of pairs of Poisson structures are introduced to study the diversity of pairs of Poisson structures incompatible in Magri's sense. It is proved that if a dynamical systemV preserves two strongly dynamically compatible Poisson structuresP ₁ andP ₂ in a general position then this system is completely integrable. Such a systemV generates a hierarchy of integrable dynamical systems which in general are not Hamiltonian neither with respect toP ₁ nor with respect toP ₂. Necessary conditions for dynamical compatibility and for strong dynamical compatibility are derived which connect these global properties with new local invariants of an arbitrary pair of incompatible Poisson structures.Supported by NSERC grant OGPIN 337.     

N.M.R. studies of cis-1,2-difluoroethylene and vinyl fluoride in a nematic solvent

Constrained anisotropic dipole oscillator strength techniques are used to obtain reliable values for a wide range of anisotropic and isotropic dipole properties of NO, including most anisotropic components of the dipole-dipole dispersion energy coefficients for the interaction of NO with NO, O₂, H₂, N₂, CO, He, Ne, Ar, Kr and Xe. Some of the anisotropic constraints required for our calculations are obtained via dipole sum rules from ab initio, multi-reference configuration interaction wavefunctions for NO. The individual dipole properties of NO considered include the dipole oscillator strength sums S_k , k = 2,1,0(? 1/2)? 2,? 3,? 4,..., the logarithmic dipole sums L_k and mean excitation energies I_k , k = 2(? 1)? 2, and, as a function of wavelength, the dynamic polarizability and its anisotropy, the total depolarizaiton ratio, and the Rayleigh scattering cross-section. Our constrained dipole oscillator strength results are often the only reliable, and often the only available, values for many of the properties and dispersion energies considered.     

Nematic-phase N.M.R. investigation of rotational isomerism: conformations of 2-furanaldehyde

An unrestricted Hartree-Fock molecular orbital procedure has been used to compute some properties of the lowest-lying spectroscopic states of NH₂, BH₂ and CH₂ ⁺. Computed bond angles for the ²B₁ and ²A₁ states of NH₂ and BH₂ are in good agreement with experimental data; bond lengths are about 6 per cent too great. Among other states for which predictions are made, the ²B₂ state of NH₂ has novel equilibrium geometry, with a predicted angle of 26·57°.

Dissociation products are considered. It is predicted that for the isoelectronic systems CH₂ ⁺ and BH₂ there is a contrast:

Other properties, such as isotropic coupling constants, force constants and dipole moments, are also reported.     

Origins of Life in the Universe,by R. Jastrow and M. Rampino

In 1903 F. Heusler reported that it was possible to make ferromagnetic alloys from non-ferromagnetic constituents copper-manganese bronze and group B elements such as aluminium and tin. Further investigations showed that the magnetic properties of these alloys are related to their chemical, L2₁, structure, and to the ordering of the manganese atoms on an f.c.c. sublattice.

Heusler alloys are properly described as ternary intermetallic compounds and they can disorder in a variety of ways. A review is given of the effects of disorder on the intensities of superlattice lines, and of the use of x-ray and neutron diffraction to determine quantitatively the extent and types of long-range chemical and magnetic order in Heusler alloys.

As Heusler alloys exhibit most of the properties of metals but have the structure of an ordered compound, it is possible that several different magnetic exchange mechanisms may be operating. A review is given of the principal theories that have been employed to explain their magnetic properties, and some of the more recent results are discussed in terms of the generalized molecular field theory.     

Particle size effect of a.c. superconducting properties in compound

Using a new starting material of Ba₂Cu₃O₅ and a three step heat treatment, single phase Tl₂Ca₁Ba₂Cu₂O₈ high- superconducting samples have been prepared, possessing the onset- and critical temperatures K and K. The morphology dependent value of is 17 Oe, 8 Oe and 5 Oe at 77 K in the case of bulk, crushed and powdered materials, respectively. The a.c. susceptibility, r.f. susceptibility and microwave absorption properties show a significant dependence on the particle size with a sharp change in the interval between 750 μm and 1200 μm. These experiments provide characteristic parameters for intergrain material (treated as 3D Josephson network) as mm, Oe and A/cm² at 77 K. The data are controlled by modulated microwave absorption measurements. The results obtained can be explained well both by the finite size junction model and cavity mode absorption model. The Josephson network is determined unambiguously by metallic S-N-S weak links. Received 10 October 1998     

Gibbs vs. Shannon entropies

The Gibbs neg-entropy -η_G=∫ II ln II is compared to the Shannon negentropy η_s=∑p Inp. The coarse-grained density is II, whilep is a probability sequence. Both objects are defined over partitions of the energy shell within a set-theoretic framework. The dissimilarity of these functionals is exhibited throughη _G vs._G η _S curves. A positive information interpretation of η_G is given referring it to the maximum information contained in the solution to the Liouville equation. The physical relevance ofη _G over η_S in classical physics is argued. In quantum mechanics, the fine-grained Shannon entropy remains relevant to the uncertainty principle, while the coarsegrained densities maintain their properties as in the classical case.     

Damage processes in Fe 3 O 4 magnetic insulator irradiated by swift heavy ions. Experimental results and modelisation

The behavior of the magnetic properties of magnetite Fe₃O₄ irradiated by swift heavy ions is investigated by magnetization measurements. Although there is no induced structural phase transformation, both coercive field and saturation magnetization are sensitive to ion irradiation and exhibit different behaviors depending on the ion fluence range. In the low fluence regime, the coercive field increases, which is evidence for a strong pinning of magnetic domain boundaries by the induced defects. The magnetization shows a decrease in the saturation value and tends to reorient perpendicularly to the ion track axis. At high fluence, the initial magnetic properties of the sample are nearly restored. The changes in the magnitude and the direction of magnetization are interpreted by magnetostrictive effects related to the stress induced by irradiation. A phenomenological model is applied to reproduce the fluence evolution of the saturation magnetization, assuming relaxation of the stress induced around the core of defects of the tracks by overlapping effects at high fluence. The results are compared to those obtained in the case of yttrium iron garnet Y₃Fe₅O₁₂. Received 18 April 2001 and Received in final form 24 July 2001     

High pressures, low temperatures, and magnetic field effects on AgFeAsSe3 and AgFeSbSe3 properties

A procedure for synthesizing AgFeAsSe₃ and AgFeSbSe₃ is presented, and their electric and magnetic properties are investigated over a wide range of temperatures, pressures, and magnetic field variation. At 100–400K, the samples are characterized by semiconductor properties. Under pressures of ～25 and ～24 GPa, the electric properties of AgFeAsSe₃ and AgFeSbSe₃ change greatly.     

Defects responsuble for electrical property changes in irradiated oxides

Abstract

A comparison is made between the activation energies for post-irradiation thermal recovery of electrical properties of NiO, Cr₂O₂ and UO₂-SiO₂ which were determined from previously published data, and the activation energies found in the literature for volume diffusion of the component atoms. It is shown that oxygen vacancies are most probably responsible for irradiation-induced changes in electrical properties of NiO and Cr₂O₂. Oxygen defects contribute also to the changes in electrical properties observed at UO₂-SiO₂.     

Cover Picture: Ann. Phys. 4'2013

The vibrational and electronic properties of a new class of organometallic sandwich molecules have been studied using first principles density functional techniques (DFT). Spectral properties as well as the HOMO‐LUMO gap energy in molecules containing up to eight C₆ layers have been calculated. S. L. Kuzmin and W. W. Duley show that infinite chains should have excellent metallic properties. These molecules are promising for nanoelectronic applications, due to their predicted high stability, conductivity, and magnetic properties (pp. 297–308).     

Field theory onR×S 3 topology. II: The Weyl equation

A Weyl-type equation onR×S ³ topology is derived, as a generalization to previously obtained Klein-Gordon- and Schrödinger-type equations for the same topology. The general solution of the new equation is given as an expansion in the matrix elements of the irreducible representations of the groupSU ₂. The properties of the solutions are discussed.Supported in part by the Colgate Research Council.