Kinetic effects in the mechanically activated solid-state reduction of haematite

Nanometer-sized -Al₂O₃-Fe composites were obtained by solid-state reduction in ball mills of Fe₂O₃ and Al in nitrogen and air. Together with -Al₂O₃ and Fe, the formation of Hercynite and clusters of Fe in alumina are observed in both cases.     

Characterization of the Laves Phases Zr(Cr,Fe)2 Oxidized in an Open Furnace Using Mössbauer Spectroscopy

Three Laves phases Zr(Cr_0.40Fe_0.60)₂, Zr(Cr_0.95Fe_0.05)₂ and Zr(Cr_0.15Fe_0.85)₂ were characterized when oxidized 7 min using Analytical Electron Microscopy (AEM), X-ray diffraction (XRD) and Mössbauer spectroscopy (MS) techniques. The first sample occurs as a hexagonal structure (C14) the other two as cubic (C15) structures. Oxidation modified them but their corresponding Laves phases still, remained. Besides, Zr_2–x O _x , Cr oxides, -Cr, (Fe, Cr) oxides, -Fe and -Fe₂O₃ were formed in the Fe-rich samples at variance of the Cr-rich one, in which -Fe and -Fe₂O₃ were absent. The appearance of -Fe supported the model previously suggested for the oxidation of the Laves phases. Results also suggested that future oxidation times have to be chosen accordingly to the composition of the Laves phases to follow stages of their oxidation.     

57Fe Mössbauer spectra study of coated α-Fe2O3 nanoparticles

Nano-sized -Fe₂O₃ particles coated with polar organic molecules have been studied using the Mössbauer spectroscopy method. The -Fe₂O₃ nanoparticles were prepared by the microemulsion method. The average particle size of the Fe₂O₃ particles is about 24 Å. Because the particle size is so small that the Mössbauer spectra of the -Fe₂O₃ samples only consist of a quadrupole-split central line. It was proved that the Isomer Shifts (DIS) and the Quadrupole Splitting (DQS) changed as the refluxing time prolongs and the refluxing temperature increases during the preparation of the Fe₂O₃ nanoparticles, which implied an enhancement of the surface electrofield gradient formed by the surface coated polar molecules during the refluxing process.     

On the oxygen isotope effect and apex anharmonicity in high-T c cuprates

Emphasis is put on aprecise knowledge of the oxygen isotope shift exponent _O is the so far synthesized high-T _c superconductors in order to elucidate the basic mechanism. The known data, see _a in Table 6, indicate the presence of a presumably anharmonic coupling of pyramidal apex oxygen motion along thec-axis in these highly in-plane correlated superconductors. _a is computed from _O=r _a , based on the conjecture that the ratior of apex to total oxygen-ion content per unit cell is relevant. The related experimental and theoretical literature is reviewed.     

Crystalline growth of cubic (Eu, Nd):Y2O3 thin films on α -Al2O3 by pulsed laser deposition

In this paper we report on the growth of crystalline, europium- and neodymium-doped cubic yttria ((Eu,Nd):Y₂O₃) thin films on hexagonal corundum (-Al₂O₃ ) substrates using the pulsed laser deposition (PLD) technique. A KrF excimer laser was used to ablate material from ceramic (Eu, Nd):Y₂O₃ targets. The yttria films were deposited on the -Al₂O₃ (0001) substrates. X-ray diffractometry (XRD) revealed that the films grew in the Y₂O₃[111]-direction. The surface topography of the films was investigated using atomic force microscopy (AFM). PACS 81.15.Fg; 42.70.hj; 68.55.Jk     

119Sn Mössbauer spectroscopy in nanocrystalline aluminat-in composites synthesized by direct grinding and reactive ball milling

Alumina-tin nanocomposites have been synthesized by direct grinding of -Al₂O₃--Sn powder mixtures, as well as by reactive milling of Al-SnO₂ mixtures. According to the preparation method used, the composites differ from one another mainly in the amount of a disordered SnO_x (x1.1) phase and in the structural characteristics of alumina.     

Reduction of optical absorption at a wavelength of around 0.8 μm in LPE garnet (TmBiCa)3(FeGaPt)5O12

Liquid-phase epitaxy (LPE) garnet films (TmBiCa)₃(FeGaPt)₅O₁₂ have been grown using only Bi₂O₃ as the flux so that the film containing Bi gives high specific Faraday rotation. The film does not contain Pb, which may affect optical absorption. The optical absorption coefficient at 810 nm has been effectively reduced by doping Ca in the melt. Our data show that a minimum level of and of the anisotropy constantK _u and also the maximum of the electrical resistivity are achieved when Ca²⁺ replaces Fe²⁺. Fe²⁺ results from Pt⁴⁺ incorporation in the film due to a Bi₂O₃ flux attack on a Pt crucible. Using a compensated film, of 58 cm^–1 and a figure of merit of 9deg/dB were obtained.     

Key resonant states in the8Li(α,n)11B reaction in the inhomogeneous big bang models

The resonant states in the key reaction⁸Li(,n)¹¹B for the inhomogeneous Big Bang Models were studied experimentally through the⁹Be(,p)¹²B reaction at 64 MeV. This reaction is found to excite all the resonances of interest in¹²B. The most crucial resonant state at 10.572 MeV in¹²B (0.572 MeV above the threshold) was found to have _tot20±10 keV and J=(1^–), suggesting that the S-factor of the (,n) process should be larger than that obtained before.     

Static and stationary axially symmetric gravitational fields of bounded sources II. solutions obtainable from Weyl's class

This paper shows that a new class of axially symmetric static electrovacuum/magnetovacuum solutions is obtainable from Weyl's class of static vacuum solutions. The new class contains an infinite set of asymptotically flat solutions (in closed form) each of which involves an arbitrary set (d, _i) of parameters. These parameters have to be interpreted as functions of massm, chargee, and higher electric/magnetic multipole moments _i of the particle. The cased = 0, _i =0 leads to the Darmois solution and the cased = 0, _i 0 leads to the results of [1]. The case d=0, e=_i=0 leads to the Schwarzschild solution, the cased 0, _i =0,e 0 leads to the Reissner-Nordström solution. To get more general examples is a lengthy but straightforward exercise.     

Rare earth doped α-alumina thin films prepared by pulsed laser deposition: structural and optical properties

-Al₂O₃ films doped with about 1% Eu³⁺ were grown on sapphire (012) substrates by pulsed laser deposition using an ArF excimer laser under 10^-4 mbar oxygen pressure and at temperatures higher than 1050 °C. The Eu doping rate was measured by Rutherford backscattering spectroscopy. The crystalline structure was determined by X-ray diffraction and transmission electron microscopy. The films are grown epitaxially on the sapphire substrate. The Eu³⁺ fluorescence spectra are constituted of narrow lines. By means of pulsed laser deposition, Eu³⁺ ions may be introduced into a single site of the -phase lattice, with a concentration that cannot be reached using conventional crystal-growth methods. PACS 81.15.Fg; 68.37.Lp; 78.55.Hx     

Mössbauer effect study of the Β-FeOOH to α-Fe2O3 phase transformation

-FeOOH was precipitated from a chloride solution. Mössbauer spectra were taken at room temperature (RT) and at 4.2 K in zero field and in external magnetic fields. Samples aged for successively longer time periods were studied. They contain -FeOOH and -Fe₂O₃, the Mössbauer spectra of which show superparamagnetic behavior. The transformation into -Fe₂O₃ is already induced by aging in the mother solution at 100 C. A final heat treatment at 350 C leads to the complete transformation into -Fe₂O₃ and to an increase of the crystallite size.     

Generalized Preisach model of hysteresis — theory and experiment

A new approach to the Preisach hysteresis model is presented. Special attention is focused on the analytical expression of the model function. -Fe₂O₃ natural sample is used to demonstrate the model, and the latest findings in the problem of the stability of the Preisach diagram are discussed.     

Short-range order and ordering energy in α solid solutions of the copper-aluminum system

The ordering energy for annealed samples of CuAl is calculated from the experimental coefficients ₁ on the basis of the statistical theory for short-range order. The short-range order is studied as a function of the quenching temperature for CuAl alloys containing 11.9, 14.3, 15.9, and 17.6 at.% Al by means of diffuse scattering of x-rays. The experimental temperature dependences of the short-range order coefficient, ₁(T), are compared with the theoretical curves.Translated from Izvestiya VUZ. Fizika, No. 3, pp. 35–40, March, 1970.     

Relativistic Hypernuclei: Old Problems and New Prospects

The first experiments with relativistic hypernuclei (Bowen; Khorozov and Lukstins) were done many years ago. They demonstrated not only that such extremely difficult experiments are manageable but also their great advantage, a possibility of observing and studying independently the production and weak decay of hypernuclei: the points of the production and decay of relativistic hypernuclei are separated by tens of centimeters instead of some microns in classical experiments. At the same time these first experiments revealed a huge problem with selection of the proper trigger.Recently we proposed to explore a unique feature of the ⁹Be nucleus: after removing a neutron from its ground state several groups of alpha-particles appear from different excited states of a residual nucleus ⁸Be. Detection of the correlated pair of -particles produced in a vacuum volume at a distance of some 40 cm from target is an unambiguous signal of nonmesonic decay of hypernucleus ¹⁰ Be(++n+n) or ¹⁰ Be(++n+p). In this particular case it is possible to take exclusive decay rates (on different excited states of ⁸Be^*). This open a way for a phenomenological analysis of matrix elements of the four-baryon weak interaction.The experiment is approved for new accelerator Nuclotron at JINR, Dubna.     

Mosaic Structure of (001)YBa2Cu3O7-δ/(10.2)Al2O3 Epitaxial Films and Millimeter Waveband Properties of Microstrip Resonators

The c-axis single-phase YBa₂Cu₃O_7- films ( = 0-0.15) on sapphire substrates prepared by the laser ablation technique and the band-pass stripline resonators for 34 GHz-range have been investigated. Increasing disorientation of mosaic block structure of YBa₂Cu₃O_7- films is related to increasing surface resistance R_s at 135 GHz-range and decreasing unloaded quality factor Q_o of linear stripline resonators. The linear dependence between the YBa₂Cu₃O_7- film mosaicity (M) and half-width B₁ of 00.13 reflecting component is determined. The reflection spreading is due to microstrains resulted mainly from the coherent adjustment of the YBa₂Cu₃O_7- film lattice to GdBa₂Cu₃O_7- sub-layer and sapphire substrate. Increasing number of the block characterized by a weak radial lattice adjustment () is demonstrated by spreading of 00.13 reflection. It is found out that depends on the Bragg angle of reflection due to inhomogenity of YBa₂Cu₃O_7- mosaic structure, which resulted from the gradual mosaicity decreasing with the depth.     

Low temperature properties of magnetic films

The effect of surface oxides on the low temperature magnetic properties of permalloy films is reviewed. Emphasis is placed on the work of Hagedorn and Mitchell and coworkers. It is shown that the unidirectional anisotropy in permalloy (typically exhibited at temperatures below 40 °K) can be correlated with the presence of -Fe₂O₃ as detected in electron diffraction studies. A possible mechanism for the phenomena is discussed which hinges on the depression of the Morin transition in -Fe₂O₃ as a consequence of a change in thed spacing of the -Fe₂O₃.The author would like to thank Professors L. D. Roberts and C. S. Smith of the University North Carolina for their helpful discussions during the course of this work.     

Mössbauer spectroscopy study on the hydrothermal transformation α-FeOOH→α-Fe2O3

The reaction kinetics of the hydrothermal transformation -FeOOH-Fe₂O₃ was studied by means of Mössbauer spectroscopy. From the reaction isotherms, a monomolecular, first order reaction was found to characterise the hydrothermal transformation of alpha oxihydroxide to the alpha iron oxide. The rate constant as well as the activation energy of this process were determined. No intermediate phases were identified in the hydrothermal samples. The thermodynamic properties of the hydrothermal system -FeOOH-Fe₂O₃ in correlation with Mössbauer spectroscopy data are discussed.     

Spatial distribution of elements of charged Frenkel defect pairs in alkali-halide crystals

Ion vibrations in alkali-halide crystals are investigated by the molecular dynamics method during decay of the molecular ion X ₂ ^– . The high efficiency of the athermal separation of the -, I-pair by displacement of the dynamic crowdion that is formed during decay of the molecular halide ion from the pre defect state or during charge-transfer of the F-, H-pair during their separation is proved. It is established that -, I-pairs are stable to annihilation if at the time of formation they turn out to be separated by a distance exceeding two interstial spacings.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 21–25, March, 1989.     

Contribution ofd-like states to magnesium,aluminium and phosphorusL-emission bands of MgO,Al2O3 and AlPO4

We have measured the MgL-, AlL- and PL-emission bands of MgO, -Al₂O₃ and AlPO₄, respectively. For MgO and Al₂O₃ the electronic structure and the X-ray emission bands have been calculated. In spite of different crystal structure and chemical composition of these compounds the cationL-emission bands are very similar. We have found that for the interpretation of theL-emission bands of these compounds the cation 3d-like electrons are crucial.     

High-power diode-cladding-pumped Tm<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript>-doped silica fibre laser

The fundamental characteristics of a continuous-wave high-power diode-pumped Tm³⁺, Ho³⁺-doped double-clad silica fibre laser are presented. A maximum output power of 5.2 W was measured and was generated at a slope efficiency of 42 (44)% with respect to the launched (absorbed) pump power. At the optimum length of 7 m (_effL=2.9, where _eff is the effective absorption coefficient of the fibre and L is the fibre length), the fibre laser output was measured to have a centre wavelength of 2105 nm and a line width of 20 nm. The centre wavelength of the emission was tunable over a 32-nm extent when 0.68<_effL<3.28 or for a 6.2-m change in L. PACS 42.55.Wd; 42.55.Xi; 42.60.Lh; 42.60.Pk