Preparation of nanostructured Ti4O7

Nonstoichiometric Ti₄O₇ titanium oxide nanopowder consisting of isolated stable nanoparticles with an average size of 115 ± 30 nm has been prepared by two-step synthesis from metallic titanium and oxalic acid. The nanostructured precipitate obtained by reacting titanium and oxalic acid was reacted with flowing hydrogen at a temperature of 1170 K to give Ti₄O₇. The proposed method allows one to control the average size of titanium oxide nanoparticles.     

Evaporation from molten TiC x

A new floating zone technique for keeping a molten zone composition constant has been developed. Using this new technique, the evaporation composition and the evaporation rate could be easily obtained as a function of molten TiC _x composition in the range of 2800 to 3100° C. In addition, the dependence of the evaporation rate on the ambient helium gas pressure was examined in the range of 3.6 to 32 atm.     

Anomalous Hall Effect in Sn1−x−y Mn x Eu y Te and Sn1−x−y Mn x Er y Te Mixed Crystals

The Anomalous Hall Effect (AHE) was investigated in IV–VI ferromagnetic semimagnetic semiconductors of Sn_1?x Mn _x Te codoped with either Eu or Er. The analysis of experimental data is as follows. Hall resistivity and magnetization showed that AHE coefficient R _s depends on temperature and its value decreases with thetemperature increase. We observe that above ferromagnet–paramagnet transition temperature R _s changes sign. We discuss the possible physical mechanisms responsible for observed temperature dependence of R _s , particularly change of the sign.     

Synthesis and properties of Sr1 − x M x Co0.8 − y Al y Fe0.2O3 − z perovskite-like oxides

Partial isomorphous substitutions on the strontium and cobalt sites in the SrCo_0.8Fe_0.2O_{3 ? z} perovskite have been shown to have a significant effect on its properties. Aluminum substitution for cobalt suppresses the brownmillerite-perovskite structural phase transition, stabilizes the cubic perovskite structure in a wide range of oxygen stoichiometries, and markedly enhances the thermal stability of the material in reducing atmospheres, without reducing the oxygen mobility. Partial lanthanum and calcium substitutions for strontium lead to the formation of Sr_{1 ? x} M _x Co_0.5Al_0.3Fe_0.2O_{3 ? z} (M = La, Ca) perovskite-like oxides, which have cubic and orthorhombic structures, respectively. The Sr_{1 ? x} La _x Co_0.5Al_0.3Fe_0.2O_{3 ? z} perovskites possess high chemical stability in reducing atmospheres and are potentially attractive as materials for oxygen-permeable membranes of catalytic methane-to-syngas conversion reactors.     

Synthesis of Fe x O y nanoparticles during iron oxidation by supercritical water

It is established that iron is oxidized by supercritical water (SCW) with the formation of H₂ and nanoparticles of iron oxides (Fe₃O₄, FeO, and γ-Fe₂O₃). The kinetics of H₂ production and iron oxidation has been studied by SCW injection at T = 673, 723, 773, 823, and 873 K into a reactor with iron particles. Data of X-ray diffraction and transmission electron microscopy show that the phase composition and morphology of synthesized oxide nanoparticles depend on the SCW temperature.     

Single-crystal K x (Zn y Ti8−y )O16 priderites: growth and characterization

Single crystals of K _x (Zn _y T_8–y O₁₆ priderites have been grown from a melt of K₂O-MoO₃ using the flux-zone technique. High-purity crystals > 10 mm in length were obtained, with no indication of twinning. Lattice parameters of a=1.0162(8) nm and c=0.2971(7) nm were obtained from X-ray diffraction measurements. Habit planes were identified from scanning electron microscope images. X-ray photoelectron spectroscopy confirmed the titanium oxidation state as +4. High-temperature complex impedance spectroscopy between 300 and 820 K was used to electrically characterize the crystals. This indicated that the materials had a low d.c. conductivity and a conductivity of 1.68×10^–3 S cm^–1 at 100 kHz.     

Preparation of nanostructured NiFe2O4 catalysts by combustion reaction

Nanosize nickel ferrite powders (NiFe₂O₄) have been prepared by combustion reaction using nitrates and urea as fuel. The resulting powders were characterized by X-ray diffraction (XRD), nitrogen physical adsorption (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and catalytic activity. The results showed nanosize nickel ferrite powders with high specific surface area (55.21 m²/g). The powders showed extensive XRD line broadening and the crystallite size calculated from the XRD line broadening was 18.0 nm. The nickel ferrite powder presented significant activity as catalyst for the water gas shift reaction, over the temperature range of 250–450 °C.     

Synthesis of new materials by laser pyrolysis: ZrO2, Y2O3:Ce and TiC(x)N(y) nanoparticles

New developments concerning the synthesis of oxide and non oxide nanoparticles by laser pyrolysis are reported here. In order to be able to study the relations between the host and the guest in doped nanostructured luminescent oxide matrix, tetragonal ZrO2 nanoparticles were synthesized with sizes as low as 3 nm in weighable amounts. Y2O3 nanoparticles doped with Ce were also prepared with grains in the 10-20 nm size range. Concerning the non-oxide materials, TiC, TiN, and TiC(x)N(y) nanopowders were obtained from simple annealing treatments performed on TiO2/C nanocomposites grown by laser pyrolysis. The final crystalline phase was controlled by the initial C content and the annealing atmosphere. Once sintered, these materials will allow the study of the mechanical properties of nanostructured carbonitride ceramics.     

不同Ti／Ba摩尔比的钛酸钡纳米晶粉体的Sol—gel法制备与表征

采用Ｓｏｌ－ｇｅｌ法制备了不同Ｔｉ／Ｂａ摩尔比的ＢａｙＴｉｘＯ３（ｘ／ｙ＝０．９９０,１．０００,１．０１０,１．０２０,１．０４５）纳米晶粉体。应用热分析、Ｘ射线粉末衍射、激光和透射电镜等技术对干凝胶热分解历程和粉体性能进行了研究,发现随Ｔｉ／Ｂａ摩尔比的增加,粉体的平均晶粒尺寸、晶体结构和粉体粒度分布各呈现规律性变化。本文并对这些规律性变化进行了初步讨论     

Electrical resistivities in single crystals of TiC x and VC x

TiC _x and VC _x have wide non-stoichiometric composition ranges which come only from the carbon vacancies. High purity single crystals with controlled compositions were prepared, and their electrical resistivities at 4.2 and 298 K were measured as a function of composition. In the case of TiC _x whose carbon vacancies are disordered in the lattice, the dependence of the residual resistivity on the composition was interpreted' by applying Nordheim's rule to the vacancy scattering and by considering the change in carrier density due to the introduction of vacancies. In addition, the difference in the resistivity between 4.2 and 298 K was discussed. In the case of VC _x whose carbon vacancies are ordered, the dependence of the resistivity on the composition ranges of the ordered phases was examined in detail.     

The effect of stoichiometry on the stability and a.c. electrical properties of Li x Ni1−y Co y O2−δ and Li x Ni1−y Co y O2−δ -Al2O3 composites at elevated temperatures

Polycrystalline samples of Li _x Ni_1−yCo_yO_2−δ(x=0.6, 0.9 and y=0.5, 1, with δ ≪ 1 depending on the stoichiometry) with and without the addition of 50 wt% α-Al₂O₃ were prepared and examined by XRD, TGA, DTA and a.c. electrical techniques. Li_xCoO₂ and its mixture with α-Al₂O₃ is unstable above 1050 K. Materials containing Ni were stable up to 1173 K and no interaction with α-Al₂O₃ was found after 6 h at 1173 K. Maximum conductivity in Ar was obtained for Li_0.9Ni_0.5Co_0.5O_2−δ between 100 Hz and 1 MHz up to 950 K. The high temperature conductivity of Li_0.9Ni_0.5Co_0.5O_2−δ could be modified with the addition of α-Al₂O₃ to render it suitable for an RF reactor. At 650 K the conductivity reversibly increased in CO₂ and rapidly decreased in H₂ followed by a slow increase on removal of H₂, behaviour typical of a p-type semiconductor. At 870 K the conductivity increased in H₂ due to slow and irreversible reduction of the oxides.     

Superstructures in Ba0·6K0·4BiO3−y and BaPb1−x Bi x O3−y

The perovskite compounds Ba_0·6K_0·4BiO₃ and BaPb_1−x Bi _x O₃ (x=0·9, 0·5, 0·25) have been investigated by high resolution electron microscopy and selected area electron diffraction. Several superlattices produced byin situ electron beam reduction have been observed. Ordered atomic arrangements in the reduced materials are discussed.