Multiferroid properties of hexagonal barium ferrites

Samples of BaFe₁₂O₁₉ with high multiferroid properties at room temperature (maximum polarization P_m = 48.0–9.5 μQ/cm², residual polarization P_r = 28.0–29.5 μQ/cm², and electric coercive field Е_c = 115–120 kV/m) have been obtained for the first time using a modified ceramic technology (based on highpurity raw materials and sintering in an oxygen atmosphere with a B₂O₃ addition). A mechanism for the explanation of the multiferroid properties obtained has been suggested; the large practical importance of the results obtained is noted.     

Multiple beam direct lattice imaging of the hexagonal ferrites

A wide variety of stacking sequences has been studied by means of transmission electron microscopy in the hexagonal ferrites of the type M_nY_m. On comparing, for a given specimen, the stacking sequences as deduced from X-ray diffraction with the image obtained in the electron microscope it was possible to establish simple “imaging codes” applicable under different diffraction conditions.The observations are in agreement with the structural features derived from X-ray diffraction. A number of known stacking sequences has been confirmed and a number of new ones has been found as well.The structural features of the hexagonal ferrites are reinterpreted in terms of repeated, polysynthetic twinning, the twin plane being localized in the center of the M block. Such an interpretation is suggested by the electron microscopic observations. Twinning is accompanied by a change in composition: it is therefore called nonconservative twinning. It is in fact analogous to crystallographic shear in accommodating deviations from simple stoichiometry. The generation of regular twinning sequences is tentatively interpreted in terms of the growth process.     

M，W型六角钡铁氧体化学键性质和穆斯堡尔谱位移研究

利用电介质的平均能带模型研究了M型、W型六角铁氧体的化学成键性质,计算了各晶位的共价性的穆斯堡尔同质异能位移,结果与实验值一致,确定了Fe^2+在W型铁氧体中所占晶位。     

Determination of ferrous ion in microsamples of hexagonal ferrites

Summary A sensitive and accurate method is described for determining microgram amounts of ferrous iron associated with a large excess of ferric iron and various bivalent cations, in hexagonal ferrites. Ferrous iron is complexed with bathophenanthroline, extracted into a chloroform-ethanol mixture and spectrophotometrically measured at 540 nm against a 13 v/v chloroform-ethanol mixture. Ferric iron is masked with ammonium dihydrogen phosphate. The analytical conditions are stated for determination of iron(II) in both solvents used for ferrites, viz., hydrochloric and phosphoric acids. Cobalt, copper, and nickel do not interfere if the procedures suggested are used. Ferrous iron down to 0.02% can be determined in samples weighing only a few milligrams.

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Zusammenfassung Eine empfindliche und genaue Methode zur Bestimmung von Mikrogrammengen Eisen(II) in Gegenwart eines großen Überschusses von Eisen(III) und verschiedener zweiwertiger Kationen in hexagonalen Ferriten wurde beschrieben. Eisen(II) wird mit Bathophenanthrolin komplex gebunden, mit einer Chloroform-Äthanol-Mischung extrahiert und bei 540 nm gegen eine Chloroform-Äthanol-Mischung (13 v/v) spektrophotometrisch gemessen. Eisen(III) wird mit NH₄ · H₂PO₄ maskiert. Die Arbeitsbedingungen für die Bestimmung von Eisen(II) in beiden für Ferrite verwendeten Lösungsmitteln — Salzsäure und Phosphorsäure — wurden festgelegt. Co, Cu und Ni stören die empfohlenen Verfahren nicht. Bis zu 0,02% Eisen(II) können in Einwaagen von wenigen Milligramm bestimmt werden.

     

掺杂剂对聚乙炔中孤子的影响

本文用半经验CNDO/2量子化学计算方法研究了各种掺杂剂对聚乙炔中孤子性质的影响。掺杂剂的存在使孤子的宽度变小, 且p型掺杂剂比n型掺杂剂的影响更大, 这主要是由于掺杂剂与聚乙炔链之间的电荷转移量不同造成的。     

元素掺杂对VH2解氢性能的影响

采用密度泛函理论（DFT）的第一性原理的平面波超软赝势方法,研究了Zr、Cu、Zn掺杂对VH2的电子结构和解氢性能的影响．计算结果显示Zr掺杂VH2后晶体模型的负合金形成热增加和费米能级目处电子浓度N（Ef）的减少,体系结构稳定性增强;V—H之间重叠集居数和电子密度计算也显示V-H之间相互作用增强;表明在VH2中掺杂Zr以后吸放氢最大容量增加,但解氢能力减弱．而Cu或Zn掺杂VH2以后晶体模型的负合金形成热减少和费米能级Ef处电子浓度N（Ef）增加,体系结构稳定性减弱;V-H之间重叠集居数和电子密度计算也显示V-H之间相互作用减弱;表明在VH2中掺杂Cu或Zn以后吸放氢最大容量降低,但解氢能力增强．与实验结论相符．同时Mulliken集居数计算结果还显示V-d轨道MuUiken集居数与掺杂有关,掺杂Zr以后V—d轨道Mulliken集居数减少;掺杂Cu或Zn以后V—d轨道Mulliken集居数增加．     

Effects of In, Al and Sn dopants on the structural and optical properties of ZnO thin films

Effect of In, Al and Sn dopants on the optical and structural properties of ZnO thin films have been investigated by X-ray diffraction technique and optical characterization method. X-ray diffraction patterns confirm that the films have polycrystalline nature. The thin films have (002) as the preferred orientation. This (002) preferred orientation is due to the minimal surface energy which the hexagonal structure, c-plane to the ZnO crystallites, corresponds to the densest packed plane. The grain size values of the films are found to be 29.0, 35.2 and 39.5 nm for In, Al and Sn doped ZnO thin films, respectively. The optical band gaps of the films were calculated. The absorption edge shifts to the lower wavelengths with In, Al and Sn dopants. The inclusion of dopant into films expands also width of localized states as E(UIn)>E(UAl)>E(USn). The refractive index dispersion curves obey the single oscillator model. The dispersion parameters and optical constants of the films were determined. These parameters changed with In, Al and Sn dopants.     

Effect of antimony dopants on the sorption properties of SnO2

The effects of antimony modifying additive (0.15—0.50 at.% Sb) on the electrophysical and sorption properties of SnO₂ powders with a well developed specific surface were studied in the temperature range of 25—250 °C. Small amounts of antimony (0.15 at.%) increase the conductivity of SnO₂ containing SO₂ and CO chemisorbed in the temperature range of 25—100 °C. This makes this composition promising as a sensitive element of gas sensors.     

Glass crystallization synthesis of ultrafine hexagonal M-type ferrites: Particle morphology and magnetic characteristics

This review concerns the synthesis and functional properties of ultrafine particles of M-type hexagonal ferrites prepared by the most advanced process of oxide glass crystallization. Hexaferrite phase formation during the heat treatment of multicomponent oxide glasses of various chemical compositions containing boron and/or silicon oxides as glass formers is considered. This route is useful to prepare assemblies of single-crystal strontium barium hexaferrite particles in the range of average particle sizes from tens of nanometers to several micrometers. The resulting glass ceramics and magnetic particle assemblies recovered from them are characterized by high coercive forces, approaching the theoretical limit for such compounds, and high magnetizations, close to the magnetization value for coarse-grained materials.     

Sintering and magnetic properties of Co-Nb ferrites

A series of samples of the system Co Nb_x Fe_2-x O₄ (x=0, 0.2, 0.4, 0.6 and 0.8) are prepared by the usual ceramic technique. X-ray analysis shows that they are cubic spinel (single phase). The lattice parameter, theoretical densityD _x, bulk densityD and the porosityP are measured for the samples. The magnetic susceptibility is measured and conducted with the additions of niobia. Results were evaluated on the bases of the exchange electrons at the octahedral sites.

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Zusammenfassung Mittels herkömmlicher keramischer Verfahren wurde eine Reihe von Proben des Systemes Co Nb_xFe_2-xO₄ (mitx=0, 0.2, 0.4, 0.6 und 0.8) gefertigt. Röntgenographische Untersuchungen zeigen ein kubisches Spinell (single-phase). Gitterkonstanten, theoretische Dichte D_x, Raumdichte D und das relative Porenvolumen der einzelnen Proben wurden bestimmt. Die magnetische Suszeptibilität wurde bestimmt. Die Ergebnisse wurden auf der Grundlage von Elektronenübergängen an den oktaedrischen Stellen gewertet.

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The author is indebted to Prof. Dr. A. Tawfik and Dr. G. Gaballa for their helpful discussions and cooperation during this work.     

Effect of 3<Emphasis Type="Italic">d</Emphasis>-metal dopants on the electronic properties of hexagonal titanium dioxide nanotubes

The electronic structure of hexagonal TiO₂ nanotubes doped with 3d transition metals from Sc to Zn was calculated by the linearized augmented cylindrical wave method. The calculated densities of states demonstrate that the substitution of Sc, V, Co, Cu, or Fe atoms for a part of Ti atoms leads to the decrease in the band gap width of the material from 4 to 2 eV. Such nanotubes are promising materials for creation of electrodes for electrochemical photolysis of water.     

Chemical composition and reactivity of water on hexagonal Pt-group metal surfaces

The dissociation behaviour and valence-electronic structure of water adsorbed on clean and oxygen-covered Ru{0001}, Rh{111}, Pd{111}, Ir{111} and Pt{111} surfaces has been studied by high-resolution X-ray photoelectron spectroscopy with the aim of identifying similarities and trends within the Pt-group metals. On average, we find higher reactivity for the 4d metals (Ru, Rh, Pd) as compared to 5d (Ir, Pt), which is correlated with characteristic shifts in the 1b(1) and 3a(1) molecular orbitals of water. Small amounts of oxygen (< 0.2 ML) induce dissociation of water on all five surfaces, for higher coverages (> 0.25 ML) only intact water is observed. Under UHV conditions these higher coverages can only be reached on the 4d metals, the 5d metals are, therefore, not passivated.     

Effects of different compositions from magnetic and nonmagnetic dopants on structural and electrical properties of ZnO nanoparticles-based varistor ceramics

In the current study, 20 nm zinc oxide (ZnO) nanoparticles were used to manufacture high-density ZnO discs doped with Mn and Sn via the conventional ceramic processing method, and their properties were characterized. Results show that the dopants were found to have significant effects on the ZnO varistors, especially on the shape and size of grains, which are significantly different for both dopants. The strong solid-state reaction in the varistor from the 20 nm ZnO powder during the sintering process may be attributed to the high surface area of the 20 nm ZnO nanoparticles. Although Mn and Sn do not affect the well-known peaks related to the wurtzite structure of ZnO ceramics, a few of the additional peaks could be formed at high doping content (≥2.0) due to the formation of other unknown phases during the sintering process. Both additives also significantly affect the electrical properties of the varistor, with a marked changed in the breakdown voltage from 415 V to 460 V for Sn and from 400 V to 950 V for Mn. Interestingly, the electrical behaviors of the varistors, such as breakdown voltage, nonlinear coefficient, and barrier height, are higher for Mn- than Sn-doping samples, and the opposite behaviors hold for hardness, leakage currents, and electrical conductivities. Results show that the magnetic moment and valence state of the two additive dopants are responsible for all demonstrated differences in the electrical characteristics between the two dopants.     

Catalytic properties of ferrites in oxidation reactions

Catalytic activities of ferrites MFe₂O₄ (M = Cu, Co, Ni, Mg, and Zn) and M¹ _0.5M² _{0 .5}Fe₂O₄ (M¹ = CU; M² = Co, Zn, and Mg) in oxidation of CO and ethylbenzene were investigated, and their dependences on the cation nature were established. Higher activities were observed for catalysts containing ions with variable valence (Cu, Co, and Ni). A correlation between catalytic and adsorption properties of ferrites was found.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 49–52, January, 1996.     

Effect of lithium oxide dopants on electrophysical and sorption properties of zinc oxide

The effects of lithium oxide dopants (0.5–0.8 at. % Li) on the electrophysical and sorption properties of ZnO were studied in the temperature range from 150 °C to 410 °C. The introduction of lithium increases the activation energy of the conductivity of ZnO, decreases its conductivity, and increases the amount of S0₂ sorbed. Two forms of chemisorbed SO₂ (donor and acceptor) are observed on the surface.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1096–1100, May, 1996.     

Effect of gallium oxide dopants on electrophysical and sorption properties of zinc oxide

The effect of gallium oxide dopants (0.1–0.3 at.% Ga) on the electrophysical and sorption properties of ZnO was studied in the temperature range from 19 to 350 °C. The introduction of the dopant increasing the conductivity of ZnO is accompanied by a change in the amounts of SO₂ and Cl₂ sorbed and the reactivity of zinc oxide. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 266–270, February, 1999.     

A theoretical study of the influence of dopants on the dehydrogenation properties of VH_2

Using the plane wave ultrasoft pseudopotential method based on the first-principles density functional theory(DFT),the influence on the electronic structure and dehydrogenation properties of VH2 doped with Zr,Cu and Zn has been studied.The results show that the negative heat of formation increases and the valence electron number at the Fermi level EF,N(EF) decreases in the Zr-doped model,indicating the higher stability of VH2 after Zr alloying.On the other hand,the negative heat of formation of VH2 decrease...     

Effects of composition on the solution properties of styrene–acrylonitrile copolymers

Short-range interactions between chain units of random copolymers in solution may be influenced by the composition or precisely by the distribution of sequence lengths of the same monomer units. Steric factors were derived for random copolymers of styrene and acrylonitrile with different compositions from the relation between the limiting viscosity number and the molecular weight. Mark-Houwink relations were obtained in methyl ethyl ketone (MEK) or in N,N′-dimethylformamide (DMF) at 30°C. for random copolymers containing 0.383 (Co-1) and 0.626 (Co-2) mole fraction of acrylonitrile, the expressions are: [η] = 3.6 X 10^?4 M _w^0.62, for Co-1 in MEK; [η] = 5.3 X 10^?4 M _w^0.61, for Co-2 in MEK; [η] = 1.2 × 10^?4M _w^0.77 for Co-2 in DMF. With the Stockmayer-Fixman expression, these correlations become, respectively: [η]/M^1/2 = 1.24 × 10^?3 + 8.0 × 10^?7 M^1/2; and [η]/M^1/2 = 1.70 × 10^?3 + 6.3 × 10^?7 M^1/2; and [η]/M^1/2 = 1.68 × 10^?3 + 31.3 × 10^?7 M^1/2. From the unperturbed mean-square end-to-end distances, 〈L²〉₀, determined from the first terms of the latter expressions, together with 〈L²〉_0f calculated by assuming the completely free rotation, gives the steric factor σ = (〈L²〉₀/〈L²〉_0f)^1/2 as 2.25 ± 0.05 for Co-1, and 2.31 ± 0.10 for Co-2. These values of σ are close to those for polystyrene (σ = 2.22 ± 0.05) and for polyacrylonitrile (σ = 2.20 ± 0.05). Therefore, it is concluded that the dimensions of random copolymers of styrene and acrylonitrile in solution are not significantly influenced by the composition. In other words, the unperturbed dimensions are not affected by a change in the alternation tendency between styrene units with phenyl side groups having a large molar volume and acrylonitrile units with nitrile groups responsible for the electrostatic interactions. On the other hand, the long-range interactions reflect the effect of sequence length. The Huggins constant and the second virial coefficient obtained from the light-scattering measurements have optimum values at about 0.5 mole fraction of acrylonitrile, where the greatest tendency for alternation seems to exist.