共查询到20条相似文献,搜索用时 15 毫秒
1.
S. R. Boidedaev 《Technical Physics》2010,55(10):1543-1546
The field and orientational dependences of magnetic linear birefringence in α-Fe2O3: Ga single crystals are investigated. The experimental results make it possible to refine and specify the structure and reveal
the features of technical magnetization of the modulated magnetic phase of this weak ferromagnet. It is shown that the model
of the modulated magnetic structure used in this study adequately describes the experimental situation. 相似文献
2.
Measurements of18O self-diffusion in hematite (Fe2O3) natural single crystals have been carried out as a function of temperature at constant partial pressure aO 2=6.5·10?2 in the temperature range 890 to 1227 °C. The aO 2 dependence of the oxygen self-diffusion coefficient at fixed temperature T=1150 °C has also been deduced in the aO 2 range 4.5·10?4 - 6.5·10?1. The concentration profiles were established by secondary-ion mass spectrometry; several profiles exhibit curvatures or long tails; volume diffusion coefficients were computed from the first part of the profiles using a solution taking into account the evaporation and the exchange at the surface. The results are well described by $$D_O \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 2.7 \cdot 10^8 a_{O_2 }^{ - 0.26} \exp \left( { - \frac{{542\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ From fitting a grain boundary diffusion solution to the profile tails, the oxygen self-diffusion coefficient in sub-boundaries has been deduced. They are well described by $$D''_O \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 3.2 \cdot 10^{25} a_{O_2 }^{ - 0.4} \exp \left( { - \frac{{911\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ Experiments performed introducing simultaneously18O and57Fe provided comparative values of the self-diffusion coefficients in volume: iron is slower than oxygen in this system showing that the concentrations of atomic point defects in the iron sublattice are lower than the concentrations of atomic point defects in the oxygen sublattice. The iron self-diffusion values obtained at T>940 °C can be described by $$D_{Fe} \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 9.2 \cdot 10^{10} a_{O_2 }^{ - 0.56} \exp \left( { - \frac{{578\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ The exponent - 1/4 observed for the oxygen activity dependence of the oxygen self-diffusion in the bulk has been interpreted considering that singly charged oxygen vacancies V O ? are involved in the oxygen diffusion mechanism. Oxygen activity dependence of iron self-diffusion is not known accurately but the best agreement with the point defect population model is obtained considering that iron self-diffusion occurs both via neutral interstitals Fe x i and charged ones. 相似文献
3.
It is shown that the closed shell valence electron molecular correlation energy of organic molecules in their ground states is a homogeneous multilinear function of the numbers of neutral atoms in their canonical hybridization state. The additivity is a robust feature, which holds for MP2(fc), MP3(fc) and MP4(fc) model calculations. The latter results obtained on a test set of 91 widely different organic molecules, exhibiting a whole gamut of electronic structure patterns, are excellent as evidenced by the absolute average deviation from the additivity values (AAD) of only 1.4 kcal mol?1 and R 2 = 0.999 93. The maximum absolute deviation (MAD) is 5.3 kcal mol?1. The additivity formula for the total molecular electron correlation retrieved from G3 calculations also has an excellent performance (AAD = 1.2 kcal mol?1, R 2 = 0.999 98 and MAD = 7.2 kcal mol?1). If it is taken into account that the additivity formulae require only back of the envelope calculations, these results are remarkable indeed, in particular since the G3 correlation energies span a very large range from 180.7 (methane) to 1642.8 (hexafluorocyclopropane) kcal mol?1. Comparison of the exact electron correlation energies in free atoms with the corresponding average correlation energies in molecules reveals that a substantial increase in the latter provides an important contribution in overcoming a very strong Coulomb repulsion between the nuclei. It is shown that the additivity formulae are useful in detecting some special molecular features such as strong resonance and anti-aromaticity. 相似文献
4.
A. S. Kamzin B. Stahl R. Gellert M. Muller E. Kankeleit D. B. Vcherashnii 《JETP Letters》2000,71(4):134-137
Depth-selective conversion electron Mössbauer spectroscopy was used to study magnetic properties of the thin surface layers of the α-Fe2O3 and FeBO3 single crystals. An analysis of the experimental spectra indicates that the magnetic properties of the layers at a depth of more than ~100 nm from the surface are similar to the properties of crystal bulk, and the corresponding spectra consist of narrow lines. The lines gradually broaden as the crystal surface is approached. The spectra of the ~10-nm-thick surface layers consist of broad lines, indicating a wide distribution δ=2.1 T of the effective magnetic field about its mean value of 32.2(4) T. The experimental spectra were used to determine the effective magnetic fields (H eff) for the iron ions situated in the surface layers of thickness ~100 nm. The effective fields in these layers were found to gradually decrease at room temperature (291 K) as the crystal surface was approached. The H eff values in the 2.4(9)-nm-thick surface layer of the α-Fe2O3 crystal and 4.9(9)-nm layer of FeBO3 are 0.7(2) and 1.2(3)%, respectively, smaller than for the nuclei of the ions in the bulk of these crystals. 相似文献
5.
A. V. Andrienko 《Journal of Experimental and Theoretical Physics》2000,90(3):508-516
Parametric excitation of magnetoelastic waves was investigated in the easy-plane antiferromagnet α-Fe2O3 by parallel and perpendicular microwave pumping over a wide range of frequencies, magnetic fields, and temperatures, and the parametric resonance thresholds were measured. The frequencies of the natural magnetoelastic vibrations of the sample were investigated as a function of the magnetic field and temperature. The results of the measurements were used to calculate the parameters of the magnetoelastic wave spectrum and the rate of relaxation of the excited quasi-phonons. Possible mechanisms for quasi-phonon damping were analyzed. 相似文献
6.
《Solid State Communications》1987,63(4):307-310
The combined channeling backscattering and channeling nuclear reaction analysis of the α-LiIO3 monocrystal in an electrostatic field has been performed by proton beam at different energies to identify the behaviour of Li and I ions in the crystal. The thickness of the crystal was about 2 mm and has been cut perpendicular to C-direction. The channeling parameters like half angular width and minimum yield of 〈001〉 axial channeling have been measured precisely and the channeling behaviour of different ions in the crystal has been observed and measured quantitatively first time. The ionic d.c. conductivity can be calculated from the surface peak of the aligned channeling spectrum directly. 相似文献
7.
8.
Copper-rich precipitates can nucleate and grow in ferritic steels containing small amounts of copper in solution and this affects mechanical properties. Growth kinetics, composition and structure of precipitates under irradiation are different from those under thermal ageing, and also vary with type of radiation. This implies that the interaction between radiation defects, i.e. vacancies, self-interstitial atoms (SIAs) and their clusters, and precipitates is influential. It is studied here by atomic-scale computer simulation. The results are compared with those of elasticity theory based on the size misfit of precipitates and defects, and the modulus difference between bcc iron and bcc copper. It is found that SIA defects are repelled by precipitates at large distance but, like vacancies, attracted at small distance. Copper precipitates in iron can, therefore, be sinks for both vacancy and interstitial defects and hence can act as recombination centres under irradiation conditions. A tentative explanation for the mixed Cu–Fe structure of precipitates observed in experiment and the absence of precipitate growth under neutron irradiation is given. More generally, agreement between the simulations and elasticity theory suggests that the results are not artefacts of the atomic model: both vacancy and interstitial defects in metals may bind to precipitates with weaker cohesion than the matrix. 相似文献
9.
The thermally induced solid-state syntheses of -Fe2O3 nanoparticles from iron-bearing materials (FeSO4, Fe2(C2O4)3 and almandine garnet) are described. Magnetic properties, particles size and the mechanism of the structural change of -Fe2O3 nanoparticles have been investigated using 57Fe Mössbauer spectroscopy, X-ray powder diffraction (XRD) and atomic force microscopy (AFM). -Fe2O3 nanoparticles are transformed into hematite via -Fe2O3 as the intermediate. 相似文献
10.
《Journal of magnetism and magnetic materials》1987,68(3):374-378
The Morin transaction is investigated by neutron diffraction topography on high crystalline flux-grown single crystals of α-Fe2O3. They display a widely spread transition, which is complete for some of the crystals, partial for others and even “reentrant” in one case. Topographys indicate that the transition takes place through a succession of a abrupt transitions of regions of the samples, and give images of these regions. We discuss the possible relationship between these regios and the crystal perfection. 相似文献
11.
T. M. Riseman J. H. Brewer K. H. Chow W. N. Hardy R. F. Kiefl S. R. Kreitzman R. Liang A. Macfarlane P. Mendels G. D. Morris J. Rammer J. W. Schneider C. Neidermayer S. L. Lee 《Hyperfine Interactions》1994,86(1):481-487
We present transverse fieldSR measurements of the magnetic field distribution in a mosaic of single crystal YBa2Cu3O6.95 in high fields (1.9–6.5 T) applied parallel to the crystallographicc-axis. TheSR lineshapes are shown in detail and the results of fits to the lineshapes are summarized. 相似文献
12.
Manganese oxide films have been grown by atomic layer deposition and investigated using electron diffraction and high-resolution electron microscopy (HREM). The films were deposited on the (001) surface of monocrystalline α-Al2O3. The films were found to consist of an ordered version of the hexagonal ε-MnO2 (Akhtenskite) type. Using X-ray diffraction, the cell parameters were determined to be a?=?2.75(2)?Å and c?=?4.302(5)?Å. The films are epitaxial with a specific orientation relative to the Al2O3 substrate. The [210] and [001] axes of ε-MnO2 are parallel to the [110] and [001] axes of α-Al2O3, respectively. Evidence of cation ordering was found by parallel beam electron diffraction. The ordered domains are needle shaped with widths of 2–10?nm. The unit cell of the ordered structure was found to be orthorhombic with cell dimensions a?=?2.75, b?=?4.76, c?=?4.302?Å and space group Pmnn (No. 58). 相似文献
13.
-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. 相似文献
14.
The multi-reference configuration interaction (MRCI) electronic energy calculations have been carried out on the ground state (X~1∑) as well as three low-lying excited states (~3E,~1∏,~3∏) of ZnCd dimer.Poten- tial energy curves (PECs) are therefore generated and fitted to the analytical potential energy functions (APEFs) using the Murrel-Sorbie (MS) potential function.Based on the PECs,the vibrational levels of each state are determined by solving Schr(?)dinger equation of nuclear motion,and corresponding spec- troscopic parameters are accurately calculated using the APEFs.The present values of spectroscopic parameters including equilibrium positions and dissociation energies are compared with other theoretical reports available at present. 相似文献
15.
16.
The energetics and structural, electronic and optical absorption properties of thallium nanowires, Tl n with n?=?1–18, have been investigated by employing a first-principles density functional theory in the local density approximation. The spin–orbit (SO) interaction has also been considered. We study four types of stable structures: planar, caged, pyramidal and helical. In general, the binding energy increases with the coordination number except in a few cases where the nearest-neighbours lie at comparatively larger separations. The maximum stability is seen for the helical configurations containing pentagons, hexagons, heptagons and octagons. Nanowires containing a core linear chain of atoms on the tube axis are more stable than the corresponding nanotubes having no such chains. All the wires or tubes are found to be metallic with or without consideration of the SO interaction. The electronic structures of the pentagonal-, hexagonal- and octagonal-configuration wires provide a large number of channels, which may give rise to large quantum ballistic conduction. One finds large differences between the optical absorption calculated with and without the SO interaction. Consideration of the SO interaction enhances the number of absorption peaks by approximately a factor of two. A strong and multi-peaked optical absorption, extending up to 4.0?eV including the visible region, appears for wires containing pentagons and octagons. These wires may thus be useful as a source of white radiation. 相似文献
17.
Fe ions were implanted into α-Al2O3 single crystals (sapphire) at room temperature and annealed in a reducing atmosphere. The orientation relationships (ORs) between α-Fe particles and sapphire matrix were investigated using transmission electron microscopy (TEM). All the α-Fe particles have the orientation relationship (OR) of (1 1 1)α-Fe || (0 0 0 1)sapphire and with sapphire. This OR is predicted precisely by the coincidence of reciprocal lattice points (CRLP) method. The other OR of (1 1 0)α-Fe || (0 0 0 1)sapphire and reported before is confirmed by the same method to be one of the secondary preferred orientation relationships in the α-Fe/sapphire system. 相似文献
18.
Haosheng Fei Mingyuan Gao Xicheng Ai Yangqiang Yang Tieqiao Zhang Jiacong Shen 《Applied Physics A: Materials Science & Processing》1996,62(6):525-528
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. 相似文献
19.
Abstract Hydrogen and deuterium are observed in α-Al2O3 crystals in the form of OH? and OD? radicals, respectively, which absorb in the infrared region. Infrared-absorption measurements were used to monitor diffusion of deuterons and protons in α-Al2O3 single crystals under the application of a moderate electric field parallel to the crystallographic c-axis, in the temperature range of 973—1333K. A linear dependence of the percent of exchange with both annealing time and applied voltage is observed, indicating that ionic conduction was taking place. The activation energy for the H+ D+ exchange was determined to be 2.4 eV, less than half the value obtained by pure thermal means, suggesting that under the application of an electric field the deuteron (proton) diffusion mechanism is different. 相似文献
20.
Campbell S. J. Klingelhöfer G. Kaczmarek W. A. Hofmann M. Nagel R. Wang G. 《Hyperfine Interactions》2002,139(1-4):407-416
Integral conversion electron Mössbauer spectroscopy has been used to investigate the phases and transformations which occur when -Fe2O3 is wet-milled in vacuum for up to 144 h. In addition to the transformation to off-stoichiometric Fe3–x
O4 observed previously by transmission Mössbauer spectroscopy, the room temperature ICEMS spectra reveal the presence of 10–15% -Fe2O3 on the surfaces of particles milled for more than 24 h. Time-of-flight neutron diffraction of an -Fe2O3 sample wet-milled for 200 h also provides evidence of the occurrence of a small fraction (4%) of -Fe2O3 in the milled product. The -Fe2O3 is likely to occur as a surface oxide layer and does not appear to play a significant role in the mechanochemical transformation of -Fe2O3 to Fe3–x
O4. 相似文献