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a b s t r a c tPhase selection during Ca silicide formation was discussed using the chemical potential and the effective heat of formation ( H ) models. The compositional analyses of Ca silicides were experimentally carried out in detail for both the layered and powder growth process. Based on the calculation, the Ca 2 Si phase has the largest negative H and is the first phase to form in the Ca-Si system. In addition, the total energy consideration consisting of the formation energy of each phase and interfacial energy between two adjoining phases is proposed to explain the experimental results of phase selection in the Ca silicide formation.

The CuO/Cu2O nanowire axial heterostructures were fabricated by a thermal oxidation technique in air. These nanowire structures resulted from CuO nanowire growth followed by Cu2O formation. These nanowires were divided into two regions. One is the top half part of the nanowire with CuO domains, and the other part is the bottom half of the wires with Cu2O domains. The structural property of the CuO/Cu2O nanowire axial heterostructures was clarified in detail. Both the CuO and the Cu2O have domain boundaries parallel to the growth direction. The specific relationship of the crystalline orientation between the CuO and Cu2O shows that CuO [110] or [110] is nearly parallel to Cu2O [110] mostly along the growth directions. The growth condition dependence of the morphological structure was also examined. A simple axial nanowire heterostructure fabrication technique using the compositional modification was developed.

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Orthorhombic polycrystalline Ca2Si sintered compact bulk crystals were synthesized via a two-step treatment, and the experimental evaluation of the electrical and thermoelectric properties of Ca2Si is reported for the first time. First, single-phase Ca2Si powders were synthesized by the heat treatment of Mg2Si powders under a Ca vapor. Then Ca2Si sintered compacts were synthesized by the spark plasma sintering technique using the Ca2Si powders. It was found that single-phase Ca2Si sintered compacts were obtained when the sintering was carried out at temperatures lower than 673 K with high pressure of 300 MPa. The structural, electrical and thermoelectric properties of the Ca-silicide sintered compacts and their dependence on process conditions are discussed.