K. Konstantinov

Nanosize cobalt oxides as anode materials for lithium-ion batteries

Nanosize cobalt oxides (Co3O4) were synthesised by chemical decomposition of cobalt octacarbonyl in toluene at low temperature. Electrochemical properties of as-prepared Co3O4 as anodes in Li-ion cells were tested. The nanosized Co3O4 electrode demonstrate a stable reversible lithium storage capacity of 360 mAh/g within 30 cycles. The reactivity of as-prepared Co3O4 in Li-ion cells could be attributed to nanosize particles of Co3O4 and its lithiation products.

Structural study of Al-substituted nickel hydroxide

Powder X-ray diffraction (XRD) is employed to identify the phase structure of Al-substituted nickel hydroxide, and its structural change after ageing treatment or charge/discharge cycles. The cell constants and the crystalline size of nickel hydroxides have been obtained by analysing the XRD pattern with Si as an internal standard. Results show that Al-substituted α-phase nickel hydroxide is very stable in strong alkaline medium even after 100 charge/discharge cycles.

Effect of boron powder purity on superconducting properties of MgB2

The effect of the properties of starting boron powders on the superconducting properties of MgB2 has been studied. The 92% and 96% pure powders produce lower surface reactivity and larger particle size than the 99% boron powder, as can be seen from Brunauer?Emmett?Teller (BET) and scanning electron microscopy (SEM) results, indicating that the low purity powders cannot be used to archive the same superconducting properties as those of samples made from pure 99% boron powder. However, the purity of 92% and 96% boron powders can be improved by using a simple chemical process, leading to enhanced magnetic critical current densities Jc. From x-ray diffraction (XRD) measurement, oxide impurity has been observed, which might be originated from the B2O3 phase in the boron powders. In order to get high performance MgB2, it is obviously important to control the phase composition and microstructure of amorphous boron starting powders and solid reaction conditions.

Study of structure, transport, paramagnetic and ferromagnetic properties of La0.8Sr0.2Mn1−xZnxO3 perovskite manganite

La0.8Sr0.2Mn1−xZnxO3 perovskite manganite with x = 0, 0.01, 0.03, 0.05, 0.1, 0.15, 0.3, 0.5 and 0.75 has been prepared by the solid state reaction and investigated by structural, transport and magnetic measurements. The structural characterization of the samples has been done by x-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. The x-ray powder diffraction results indicate a single phase for 0 0.1 decreases with increasing zinc doping levels. The transport measurements show that the insulator-to-metal transition temperature, Tc, decreases with increasing zinc substitution on the Mn site, and the resistivity increases. The Tc variations agree with the magnetic measurement data for x 0.3. The possible mechanism behind the effects of zinc doping into the La0.8Sr0.2Mn1−xZnxO3 system involves degradation of the double exchange between Mn3+–O–Mn4+ in this compound.

Zinc doping effects on the structure, transport and magnetic properties of La0.7Sr0.3Mn1-xZnxO3 manganite oxide

Abstract The processing, microstructures and properties of La0.7Sr0.3Mn1–xZnxO3 perovskite manganite, with x= 0; 0.1, 0.2, and 0.3 have been investigated. X-ray diffraction, scanning electron microscopy (SEM) and other characterisation methods were used to study the relations of microstructure and properties. The X-ray powder diffraction results show a single phase for the 0 < x < 0.3 region that confirms the zinc incorporation into the Mn site. The SEM images with magnification 1500 × indicate that the studied system is a singlephase. The transport measurements show decreasing of insulator to metal transition temperature, Tt; with increasing the zinc concentration on the Mn site, while the resistivity increases with increasing the zinc doping level for 0 < x < 0.1: The maximum resistivities are found at 380 and 160 K, respectively. The PPMS measurements show that the magnetisation value is greatest for x = 0.1 and drastically decrease for theparent material, as well as with increasing the zinc doping concentration above 20%, when the compound changes from ferromagnetic to paramagnetic. The paramagnetic to ferromagnetic transition temperature variations, Tc; agrees with the insulator to metal variations, Tt; from the transport measurements for the parent and 10% doped material. For zinc doping levels above 20%, the behavior of the studied system changes from ferromagnetic to paramagnetic.

Electrochemical properties of orthorhombic LiMnO2 prepared by one-step middle-temperature solid-state reaction

Orthorhombic LiMnO2 with small grain size was successfully synthesised using a one-step middle-temperature solid-state reaction (OSSS). Compared with the methods other researchers used, the OSSS method is much simpler. It is a one-step method without intermediate regrinding or other treatments. The o-LiMnO2 obtained showed a high initial capacity 180 mAh/g when cycled at a current density of 0.5 mA/cm2 at room temperature, and the rate capability was improved due to the smaller particle size. Therefore, the one-step middle temperature solid-state reaction could be a promising method for o-LiMnO2 compound synthesis.

Fabrication and properties of spray-dried nanofeatured spherical Ni(OH)2 materials.

Spherical agglomerates of nanostructured beta-phase Ni(OH)2 with the general formula Ni1-xCox(OH)2 (x = 0, 0.1, 0.3) for use as cathode materials were produced by a modified method including coprecipitation of Ni or Ni composite hydroxide and further spray drying of the precipitated and washed slurry. This process leads to the formation of spherical agglomerate particles with a narrow Gaussian-type distribution range. The method permits faster and cheaper production of cathode materials with a higher specific surface area and similar or better capacity and cycle life compared with the materials prepared via conventional technology.

Growths of MgB2 thin films by pulsed laser deposition

Abstract The recent discovery of metallic-like superconductivity in bulk MgB2 material [1] opened a new class of possible applications in current transport, magnetic field devices and electronic devices. Fabrication of thin films in situ is essential in order to explore the device applications of this material, and in spite of a few reports [2] , [3] , [4] , this still remains a challenge. The main reasons for this are the high vapour pressure of Mg even at low temperatures, and the high susceptibility of Mg to oxidation. A number of c-axis oriented MgB2 films were grown on Al2O3-R cut, and the stoichiometry of the films was measured by ICP as a function of deposition pressure and laser fluence. It was found that the relative concentration of Mg on the substrate varies considerably with pressure and laser fluence. A relative concentration of around 53 at% Mg, which is necessary in order to form stoichiometric MgB2 phase, can be obtain only in a narrow range of deposition pressures and laser fluences. The films obtain under these conditions were characterised by X-ray diffraction and magnetic moment in applied fields up to 9T.