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Abstract: We have systematically investigated magnetization, resistivity, thermopower and X-ray photoemission spectra(XPS) in LaCo1−x Ni x O3 () system. It is found that the transport mechanism is variable range hopping(VRH) for , and thermally activated hopping for . While the transport mechanism is far from the hopping process for , invalidity of the hopping process for and metallic behaviour for , indicates that the MIT is around . For samples (), the thermopower can be explained well by Cutler–Mott formula which is suitable for metal with strong disorder. The metal-insulator transition in this system is a Mott–Anderson transition in which disorder effects dominates the MIT, in the presence of electron-electron correlations. The results indicate a two-band behaviour in LaCo1−x Ni x O3. We propose possible evolution of electronic structure to explain these phenomena. [Copyright &y& Elsevier]

Abstract: Epitaxial La0.67Ca0.33MnO3 thin films deposited on (001)- LaAlO3 under different oxygen partial pressures (P O2 ) from 50 mTorr to 500 mTorr are investigated. An oxygen-deficiency-activated phase separation is observed by X-ray diffraction (XRD), microstructure and temperature coefficient of resistance (TCR) studies. The transport properties are strongly related to the strain state of films. All films show phase separation behavior except for the film deposited at 50 mTorr at which most of the strain was relieved by serious crystal defects. The films deposited at 300 and 350 mTorr show insulating behavior in the whole temperature range, which is attributed to charge-ordered (CO) state and can be suppressed by applied field. [Copyright &y& Elsevier]

Abstract: The magnetization, resistivity ρ, thermoelectric power (TEP) S, and thermal conductivity κ in perovskite cobalt oxide Gd0.7Sr0.3CoO3 have been investigated systematically. Based on the temperature dependence of susceptibility χ g(T) and Seebeck coefficient S(T), a combination of the intermediate-spin (IS) state for Co3+ and the low-spin (LS) state for Co4+ can be suggested. A metal–insulator transition (MIT) caused by the hopping of σ* electrons (localized or delocalized e g electrons) from the IS Co3+ to the LS Co4+ is observed. Meanwhile, S(T) curve also displays an obvious phonon drag effect. In addition, based on the analysis of the temperature dependence of S(T) and ρ(T), the high-temperature small polaron conduction and the low-temperature variable-range-hopping conduction are suggested, respectively. As to thermal conduction κ(T), rather low κ values in the whole measured temperature range is attributed to unusually large local Jahn–Teller (JT) distortion of Co3+O6 octahedra with IS state. [Copyright &y& Elsevier]

Abstract: Charge ordering behavior is observed in the crystal prepared through the immersion of the Na0.41CoO2 crystal in distilled water. Discovery of the charge ordering in the crystal with Na content less than 0.5 indicates that the immersion in water brings about the reduction of the Na0.41CoO2. The formal valence of Co changes from +3.59 estimated from the Na content to +3.50, the same as that in Na0.5CoO2. The charge compensation is confirmed to arise from the intercalation of the oxonium ions as occurred in the superconducting sodium cobalt oxide bilayer-hydrate [K. Takada, et al. J. Mater. Chem. 14 (2004) 1448]. The charge ordering is the same as that observed in Na0.5CoO2. It suggests that the Co valence of +3.50 is necessary for the charge ordering. [Copyright &y& Elsevier]