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Electronic Structures and Chemical Bonds of cobaltite and Ni-Doped

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Journal of Wuhan University of Technology(Materials Science) 2005年第3期20卷 48-51页

作者：闵新民 Department of Applied Chemistry Wuhan University of Technology

The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co2 O6 and Ni-doped was studied by density function theory and discrete variation method（DFT-DVM）. The results indicate that the highest valence band（ HVB ）attd the lowest conduction band（ LCB ） are mainly attribuled to Co3d, Ni3d and O2p atomic orbitals. The property of a semiconductor is shown from the gap between HVB and LCB. The gap of Ni-doped one is less than that of Ca3 Co2 O6. The non-metal bond or ceramic characteristic of Ni-doped one is weaker than that of Ca3 Co2 O6, but the metal characteristics of Ni-doped one are stronger than those of Ca3 Co2 O6. The thermoelectric property should be improved by adding Ni element into the system of Ca3 Co2 O6 .

关键词： cobaltite Ni- doped electronic structure chemical bond thermoelectric property

Effect of Substitution Degree and the Calcination Temperature on the N2O Decomposition over Zinc cobaltite Catalysts

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Modern Research in Catalysis 2017年第1期6卷 47-64页

作者： B. M. Abu-Zied S. A. Soliman S. E. Abdellah Chemistry Department Faculty of Science Assiut University Assiut Egypt

In this paper, a series of zinc cobaltite catalysts with the general formula Znx-Co1-xCo2O4 (x = 0.25, 0.50, 0.75 and 1.0) has been prepared using the co-precipitation method. Thermal analyzes (TGA and DTA) were used to follow up the thermal events accompanying the heat treatment of the parent mixture. Based on these results, the various parent mixtures were calcined at 500℃. The obtained solid catalysts were characterized by using XRD, FT-IR and N2-adsorption. The catalytic decomposition of N2O to N2 and O2 was carried out on the zinc-cobaltite catalysts. It was found that partial replacement of Co2+ by Zn2+ in Co3O4 spinel oxide led to a significant improvement in their N2O decomposition activity. Moreover, the catalytic activity was found to be depended on the calcination temperature utilized.

关键词： Greenhouse Gases Nitrous Oxide N2O Decomposition Znx-Co1-xCo2O4 Zinc cobaltite Spinel Oxide

Transition Metal-Nonmetal in Conductivity of Ceramic Hole-Doped cobaltites

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Journal of Modern Physics 2010年第5期1卷 319-323页

作者： Yurii Nikolaevich Chiang Mihail Olegovich Dzyuba Olga Georgievna Shevchenko Anatolii Antonovich Kozlovskii Vitalii Philipovich Khirnyi 不详

In bulk granulated cobaltite La1–xSrxCoO3 with the size of granules of order of 1 micron at strontium hole doping with replacement factor x = 0.35, a transition “metal-nonmetal” in the conductivity was revealed, presumably connected with AFM ordering of the moments of granules. The assumption is proved by the agreement between the experiment and results of calculation within the limits of a model offered for electron transport based on the account of in-granule double exchange Zener mechanism and intergranule mechanism of spin-polarized tunneling on the nearest neighbours with AFM exchange interaction. The calculation differs in that conductivities within granules are summarized, while total resistance of the system is represented as a sum of resistances of the granules. In addition, the existence of AFM interaction between granules is supported by the observed insensitivity of conductivity to a low external magnetic field (up to 5 kOe).

关键词： Granulated cobaltite Double Exchange Spin-Polarised Tunneling

Structural,magnetic and electrical characterization of the La_(0.7)Ca_(0.3)Co_(1–x)Mn_xO_3(x=0,0.7 and 1) compounds prepared by a simple method

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Journal of Rare Earths 2014年第10期32卷 965-972页

作者： M.Eshraghi P.Kameli F.Khalili M.H.Ehsani H.Salamati Department of Physics Payame Noor University Department of Physics Isfahan University of Technology Department of Physics Semnan University

Structural, magnetic and electrical properties of the La0.7Ca0.3Co1–xMnxO3（x=0, 0.7 and 1） samples prepared by a simple method were systematically studied and it was found that the crystal structure was transformed from rhombohedral for La0.7Ca0.3CoO3（LCCO） and La0.7Ca0.3Co0.3Mn0.7O3（LCCMO） samples to orthorhombic for La0.7Ca0.3MnO3（LCMO） sample. The AC magnetic susceptibility measurements showed that LCCO sample underwent a transition from paramagnetic（PM） to ferromagnetic（FM） phase at Curie temperature, TC^155 K and below Curie temperature, the glassy ferromagnetism nature was observed. In LCCMO sample,clear evidence of spin glass（SG） state was observed at low temperature. PM-FM phase transition at about TC^260 K and long range FM order at low temperatures were observed in LCMO sample. Both the LCCO and LCCMO samples exhibited insulating behavior in the whole range of measuring temperature whereas the LCMO sample underwent a clear metal-insulator（MI） transition at about TMI^263 K, corresponding to Curie temperature. Metallic region of ρ（T） curve of the LCMO sample was fitted to the model of electron-electron and electron-magnon scattering. The charge carrier transport behavior in all the samples was compared based on polaronic models.

关键词： cobaltite spin glass manganites rare earths

Electronic Structure and Thermoelectric Properties of Ca_3Co_4O_9

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Journal of Wuhan University of Technology(Materials Science) 2006年第1期21卷 13-15页

作者：闵新民 Department of Applied Chemistry Wuhan University of TechnologyWuhan 430070China

The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co4 O9 was studied using density function and discrete variation method （DFT-DVM）. The gap between the highest valence band （HVB） and the lowest conduction band （LCB） shows a semiconducting property. Ca3 Co4 O9 consists of CoO2 and Ca2 CoO3 two layers. The HVB and LCB near Fermi level are only mainly from O（ 2 ） 2p and Co （2） 3d in Ca2 CoO3 layer. Therefore, the semiconducting or thermoelectric property of Ca3 Co4 O9 should be mainly from Ca2 CoO3 layer, but it seems to have no direct relation to the CoO2 layer, which is consistent with that binary oxides hardly have a thermoelectric property, but trinary oxide compounds have quite a good thermoelectric property. The covalent and ionic bonds of Ca2 CoO3 layer are both weaker than those of CoO2 layer. Ca plays the role of connections between CoO2 and Ca2 CoO3 layers in Ca3 Co4 O9, decrease the ionic and covalent bond strength, and improve the thermoelectric property.

关键词： cobaltite electronic structure chemical bond thermoelectric property

CaCo1-xRuxOy: Role of Ru/Co Ratio on Its Transport Properties

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New Journal of Glass and Ceramics 2014年第1期4卷 8-17页

作者： Sezhian Annamalai Rudra P. Bhatta Jugdersuren Battogtokh Ian L. Pegg Biprodas Dutta Vitreous State Laboratory the Catholic University of America Washington DC USA Vitreous State Laboratory the Catholic University of America Washington DC USA Currently at Corninng Incorporated Corning NY USA Vitreous State Laboratory the Catholic University of America Washington DC USA Currently at Naval Research Lab Washington DC USA

Calcium cobaltites, especially Ca3Co4O9 with a misfit layered structure, are promising thermoelectric materials due to their suitability for high temperature applications and low densities. The existence of low spin-state electronic configurations for both and species is one of the key parameter to explain the large thermopower values. Ruthenium oxide, with a layered structure, exhibits strong electron-electron correlation and the extended nature of their 4d electrons enhances orbital overlapping which is expected to influence the transport characteristics of CaCo1-xRuxOy (CCR) samples, by affecting the spin state of the 3d Co ions. The effect on thermopower and electrical resistivity due to partial substitution of Co by Ru ions, up to 0.33 moles, from 300 to 600 K was investigated. A sharp decline in resistivity and in thermopower was observed until a transition ion ratio (TIR), (Ru/(Ru + Co)), of 0.5 is reached, beyond which both the properties became less sensitive to TIR. These variations in the transport properties are explained by the presence of 4d Ru in close proximity to the Co, which could influence the spin and oxidation state of Co ions. The Co rich and Ru rich samples exhibit very distinct microstructures and phase assemblages.

关键词： Calcium cobaltite Ruthenium Oxide Calcium Ruthenate Transport Properties Thermoelectric Properties Seebeck Coefficient Resistivity