Preparation Of Co-based Oxide Thermoelectric Materials

With environment and energy problems becoming rigorous, thermoelectric materials, which convert heat into electricity and vice versa through the thermoelectric phenomena in solids, have recently attracted a renewed interest as a promising energy-conversion technology that is friendly to the environment. Oxide thermoelectric materials possess some unique merits such as high temperature resistance, oxidative stability, non-pollution and non-poisonous, comparing with normal thermoelectric alloys. The thermoelectric phenomena, the history, the application domain and the recent research process of the thermoelectric materials were reviewed in detail at first.Bi-Sr-Ca-Co-0 series thermoelectric materials exhibit good thermoelectric properties, which make these compounds a promising candidate for application to power generators. The polycrystalline bulk thermoelectric materials must be prepared for practical applications.By solid-reaction method and sol-gel process, the Bi-Sr-Ca-Co-O series polycrystalline thermoelectric ceramics materials were prepared successfully in the thesis. Firstly, Bi-Sr-Ca-Co-0 compound ceramic material was prepared by traditional solid-reaction method with two kinds of sintering system. And then, Bi-Sr-Ca-Co-0 series compounds precursor powder was synthesized via sol-gel process innovatively in this thesis with three projects and two kinds of sintering system. The better project comparatively was obtained.In this thesis, the preparation process and crystal structured of Bi-Sr-Ca-Co-O series compounds were systematically investigated. The crystal series and lattice parameters of Bi-Sr-Ca-Co-O compounds were analyzed detailedly by TEM technology. The crystal structure of Bi-Sr-Ca-Co-O compounds was elementarily demarcated by the software. The phases of Bi-Sr-Ca-Co-O compounds were analysized by XRD technology. The lattice parameters and crystal structure variational with adulteration and substitution were analyzed. The surface feature of the samples was observed by microscope technology.The conclusions obtained through research work are as follows: Single phase bismuthcobalt oxide polycrystalline thermoelectric material can be prepared successfully by solid-reaction method and sol-gel process within experiments. Between the methods, the sol-gel process is much better. Bi-Sr-Ca-Co-O series thermoelectric materials are layered compounds. Bismuth cobalt oxide thermoelectric material consists of the alternate stack of CoO₂ layer (H layer) and the Rock-Salt layer (RS layer). In the experiments, calcium was adulterated to nominal Bi₂Sr₂Co₂O_y, (BC-2202) to make nominal Bi₂Sr₂CaCo₂O_y, (BC-2212) and fifty percent of strontium in Bi₂Sr₂Co₂O_y was substituted by calcium to make nominal Bi₂SrCaCo₂O_y (BC-2112), no impurities were detected. It was found that although lattice constants change with the adulteration and substitution, the crystal structure of Bi-Sr-Ca-Co-O system thermoelectric materials is stead. The c axis of BC-2202 sample lattice parameter is 1.491nm and the c axis of BC-2112 sample lattice parameter 1.473nm.