Oxide-based Compounds Research Articles

Structural characterization and phase transformations in metal oxide films synthesized by successive ionic layer deposition (SILD) method

In this paper the peculiarities of phase composition and morphology of metal oxides synthesized by successive ionic layer deposition (SILD) method are discussed. The main attention is focused on SnO2-based metal oxides, which are promising materials for gas sensor applications. FTIR spectroscopy has shown that the precipitates of metal oxides, deposited by SILD method, are hydroxide, peroxide or hydrated metal oxide-based compounds. After annealing at relatively low temperatures (200-400?C) these compounds release both water and peroxide oxygen and transform into corresponding oxides. According to XRD, SEM and AFM measurements it was confirmed that deposited films had fine-dispersed structures. Only after annealing at Tan>500?C, XRD diffraction peaks, typical for nanocrystalline material with grain size < 6-8 nm, were observed. High roughness and high degree of agglomeration are important peculiarities of metal oxides deposited by SILD. Metal oxide films consist of spherical agglomerates. Degree of agglomeration of the films and agglomerate size could be controlled. It was found that introduction of various additives in the solution for SILD could sufficiently change the microstructure of synthesized metal oxides. .

Group 4 and 5 Oxide-Based Compounds as New Cathodes without Platinum Group Metals for PEFC

A partially oxidized TaC0.58N0.42 has been investigated as a new cathode for polymer electrolyte fuel cells. The catalytic activity for oxygen reduction reaction (ORR) significantly depended on the oxidation state of the TaC0.58N0.42. TaC0.58N0.42 and Ta2O5 had a poor catalytic activity for the ORR. The onset potential on the partially oxidized TaC0.58N0.42 for the ORR had a maximum value of 0.9 V vs. RHE in 0.1 mol dm-3 H2SO4 at 30oC. XRD analysis showed that the specimens, which had a definite catalytic activity for the ORR, had both TaCxNy and Ta2O5 peaks. This result indicated that an appropriate oxidation of the TaC0.58N0.42 was essential to enhance the catalytic activity for the ORR.

Group 4 and 5 Oxide-based Compounds as New Cathodes without Platinum Group Metals for PEFC

A partially oxidized TaC0.58N0.42 has been investigated as a new cathode for polymer electrolyte fuel cells. The catalytic activity for oxygen reduction reaction (ORR) significantly depended on an oxidation state of the TaC0.58N0.42. TaC0.58N0.42 and Ta2O5 had a poor catalytic activity for the ORR. The onset potential on the partially oxidized TaC0.58N0.42 for the ORR had a maximum value of 0.9 V vs. RHE in 0.1 mol dm-3 H2SO4 at 30oC. Hard X-ray PhotoElectron Spectroscopy and XRD analyses indicated that the surfaces of the partially oxidized TaC0.58N0.42 were oxidized, although the inner parts of the partially oxidized TaC0.58N0.42 remained tantalum carbonitride. This result indicated that an appropriate oxidation of the TaC0.58N0.42 was essential to enhance the catalytic activity for the ORR.

Group 4 and 5 Oxide-based Compounds as New Cathodes without Platinum Group Metals for PEFC

not Available.

Group 4 and 5 Oxide-Based Compounds as New Cathodes Without Platinum Group Metals for PEFC

not Available.

Structural evolution and effects of calcium doping on nanophasic LaCoO3 powders prepared by non-alkoxidic sol–gel technique

The structural evolution and the effects of calcium doping on LaCoO3 powders as a function of thermal annealing were investigated by means of X-ray absorption fine structure spectroscopy from both Co and La K-edges. The samples, synthesized by a sol–gel process starting from methanolic solutions of cobalt(II) and calcium(II) acetates, and lanthanum(III) nitrate, were analysed as xerogels (as-prepared) and after heat treatment. The investigations indicated that the lanthanum cobaltite skeleton was not yet formed in the as-prepared samples whereas significant structural changes ascribable to the formation of the LaCoO3 network were detected after annealing at temperatures between 700 and 1000 °C. Doping with calcium induced remarkable influences in the local structure of the system, which are dependent on the treatment temperatures. These changes could be attributed to different effects: i) the formation of cobalt and calcium oxide-based compounds, ii) the distortion in the perovskite structure and iii) the partial substitution of La(III) sites by Ca(II) ions. The studies also indicated the change in the oxidation state of cobalt from +2 in the xerogels to +3 after annealing.

Morphological and magnetic characterization of manganites oxide-based nanowires and nanotubes

A morphological and magnetic study of sub-micrometric nanostructures of a manganese oxide-based compound La 0.325Pr 0.300Ca 0.375MnO 3 is presented. Nanowires of 50 and 100 nm and tubes with external diameters of 200 and 800 nm were synthesized. Scanning electron microscopy with EDS microanalysis (SEM) and transmission electron microscopy (TEM) allowed to characterize the morphology and microstructure of these nanostructures. The walls of the nanotubes are composed of on average 40 nm grain size particles, while in nanowires the grains are much smaller, in the range between 4 and 20 nm. In both situations, the small grains present a random crystalline orientation, as it is confirmed by TEM diffraction experiments. Magnetization measurements and hysteresis loops are presented and discussed based on magnetic interaction between the grains, anisotropy considerations and reversal magnetization mechanisms.

Phase coexistence regimes in La 0.325Pr 0.300Ca 0.375MnO 3

We studied electric and magnetic properties of polycrystalline La 0.325Pr 0.300Ca 0.375MnO 3, a manganese oxide-based compound exhibiting intrinsic multiphase coexistence of submicrometric ferromagnetic, charge-ordered and charge-disordered regions. Time relaxation in both resistivity and magnetization were observed in a broad temperature range, signaling that coexisting phases are out of equilibrium. Different regimes of instability are presented and discussed.

Synthesis route for obtaining manganese oxide-based nanostructures

Hollow and solid cylindrical nanometric structures of mixed valent manganese oxide-based compounds were obtained by wetting sacrificial porous substrates. Plastic templates with pores ranging 0.05–1 μm were employed; a two-stage thermal process was performed to obtain La 0.325Pr 0.300Ca 0.375MnO 3 or La 2/3Sr 1/3MnO 3. Polycrystalline self-standing tubes were obtained for pore size higher than 0.2 μm, while wires were obtained for diameters below 0.1 μm. We discuss the role of the template pore size in determining the synthesis route, the formation of different intermediate compounds, and different morphologies.

Using a structural criterion for the selection of red-emitting oxide-based compounds containing Pr 3+

In a number of oxide-based host lattices, the Pr 3+ ion exhibits a prominent red 1 D 2→ 3 H 4 emission instead of the usual greenish-blue luminescence from 3 P 0 level. Although different radiationless relaxation processes can contribute to the quenching of 3 P 0 emission in these compounds, all of them are more or less closely connected to the structural characteristics of the host networks. From structural and optical studies of several compounds containing Pr 3+ ions, we propose a very simple criterion, founded on the calculation of point charge electrostatic potentials involving both the first (O 2−) and second (metallic cations) coordination environments around one given Pr 3+ site in the host structures, to predict either total or partial quenching of 3 P 0 luminescence.

Magnesium diboride: one year on

AT THE end of 2000 superconductivity in metal alloys and compounds appeared to remain trapped by a glass ceiling. Over the previous 10 years the temperature at which certain oxide-based compounds – such as bismuth strontium calcium copper oxide and mercury barium calcium copper oxide – lost their resistance to electric current had soared to well over 100 K. Mean-while, the transition temperature, Tc, for carbon-based materials, including alkali-doped carbon-60 compounds, had risen close to the boiling point of liquid nitrogen (77K). During the same period, however, the superconducting transition temperature of intermetallic compounds (materials made solely of metals and metal-like elements) remained close to 20 K – as it had been since the mid-1960s.

209Bi NQR in Mixed Oxides 2Bi2O3· B2O3, 3Bi2O3· 5B2O3, and Bi2O3· 3B2O3

It was earlier found from nuclear quadrupole resonance (NQR) measurements and computer modeling that α-Bi2O3, Bi3O4Br and mixed oxides Bi2O3· 2Al2O3, Bi2O3· 2Ga2O3, Bi2O3· 3GeO2, and 2Bi2O3· 3GeO2exhibit local ordered magnetic fields from 30 to 200 G. It thus follows that these compounds are not diamagnets in a conventional sence of the word. With the aim of revealing previously unknown magnetic properties in bismuth(III) oxide-based Main Group element compounds, the mixed bismuth–boron oxides 2Bi2O3· B2O3, 3Bi2O3· 5B2O3, and Bi2O3· 3B2O3were prepared and studied using 209Bi NQR. The quadrupole interactions of the 209Bi nuclei and their electronic environment were studied, the crystallochemical features of the compounds were discussed, and the conformity of the 209Bi results to the X-ray structure data was verified. The preliminary tests in the field of a permanent magnet showed that the resonance intensities increase in external magnetic fields, indicating that a magnetism of unknown nature develops in the titled compounds. It was found reasonable to continue studies of the magnetic properties of these compounds using single-crystal 209Bi NQR in external magnetic fields.

Thin-film lithium and lithium-ion batteries

Research over the last decade at Oak Ridge National Laboratory has led to the development of solid-state thin-film lithium and lithium-ion batteries. The batteries, which are less than 15 μm thick, have important applications in a variety of consumer and medical products, and they are useful research tools in characterizing the properties of lithium intercalation compounds in thin-film form. The batteries consist of cathodes that are crystalline or nanocrystalline oxide-based lithium intercalation compounds such as LiCoO 2 and LiMn 2O 4, and anodes of lithium metal, inorganic compounds such as silicon–tin oxynitrides, Sn 3N 4 and Zn 3N 2, or metal films such as Cu in which the anode is formed by lithium plating on the initial charge. The electrolyte is a glassy lithium phosphorus oxynitride (‘Lipon’). Cells with crystalline LiCoO 2 cathodes can deliver up to 30% of their maximum capacity between 4.2 and 3 V at discharge currents of 10 mA/cm 2, and at more moderate discharge–charge rates, the capacity decreases by negligible amounts over thousands of cycles. Thin films of crystalline lithium manganese oxide with the general composition Li 1+ x Mn 2− y O 4 exhibit on the initial charge significant capacity at 5 V and, depending on the deposition process, at 4.6 V as well, as a consequence of the manganese deficiency–lithium excess. The 5-V plateau is believed to be due to oxidation Mn of ions to valence states higher than +4 accompanied by a rearrangement of the lattice. The gap between the discharge–charge curves of cells with as-deposited nanocrystalline Li 1+ x Mn 2− y O 4 cathodes is due to a true hysteresis as opposed to a kinetically hindered relaxation observed with the highly crystalline films. This behavior was confirmed by observing classic scanning curves on charge and discharge at intermediate stages of insertion and extraction of Li + ions. Extended cycling of lithium cells with these cathodes at 25 and 100°C leads to grain growth and evolution of the charge–discharge profiles toward those characteristic of well crystallized films.

Grain boundary structures in La2/3Ca1/3MnO3 thin films

As with many other oxide-based compounds that exhibit electronic behavior, structural defects have a strong influence on the electronic properties of the CMR manganites. In this work, we have studied the effect of grain boundaries on the transport properties and on the local orientation of magnetization. Thin films of the perovskite-related La2/3Ca1/3MnO3 compound were deposited onto bicrystal substrates using pulsed laser deposition. Transport measurements showed an enhancement of magnetoresistance across the grain boundary. The structure of the boundary was evaluated by electron microscopy. In contrast with the highly meandering boundaries typically observed in bicrystals of high-temperature superconductors, the boundaries in these films are relatively straight and well defined. However, magneto-optical imaging showed that the local magnetization was oriented out of the plane at the grain boundary while it was oriented within the plane in the grains on either side. This coordinated reorientation of local magnetization near the grain boundary leads to enhanced magnetoresistance across the boundary in low fields.

Evaluation of the cytocompatibility of three endodontic materials

The goal of this in vitro study was to evaluate the relative cytocompatibility of three endodontic materials: calcium hydroxide, a calcium oxide-based compound, and a zinc oxide-eugenol-based sealer. The evaluation was conducted 24, 72, and 168 h after contact with the compounds and involved three complementary techniques: a colorimetric cytotoxicity test, scanning electron microscopy, and flow cytometry. The results we obtained confirmed the initial cytotoxicity of the zinc oxide-eugenol-based sealer and showed that the calcium oxide-based compound had the same relative cytocompatibility as calcium hydroxide.

LIVER II: IRON OXIDE-BASED RETICULOENDOTHELIAL CONTRAST AGENTS FOR MR IMAGING: Clinical Review

Iron oxide-based compounds are a new class of MR contrast agents that have a wide range of clinical applications. The biodistribution and subsequent influence on the MR image depends on the particle size. Iron oxides can be used to increase contrast-to-noise ratio, facilitating the visibility of focal liver lesions. Other applications include blood-pool imaging and targeting the reticuloendothelial system and cell surface receptors.

High oxide ion conductivity in bismuth uranate, Bi 2UO 6

The layer compound Bi 2UO 6 has been prepared by co-precipitation and subjected to powder x-ray diffraction, transmission electron microscopy, impedance spectroscopy, oxygen concentration cell and oxygen transport cell measurements. At 400°C in atmospheres of O 2 or N 2, ceramic samples displayed a bulk oxide ion conductivity of 10 −1 S cm −1, about an order of magnitude higher than that of other bismuth oxide-based compounds. However, because of grain boundary blocking, the overall conductivity of the ceramic was limited to 10 −2 S cm −1. At 475 to 600°C the concentration and transport cell measurements indicated mixed oxide ion/electronic conductivity. Possible mechanisms of oxide ion transport and of grain boundary blocking are discussed in relation to structure.