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Preparation of N-type ZnO High-temperature Electrodes and First-principles Analysis of NaCo2O4

Author: ZhouDeZhi
Tutor: LiZuoZuo
School: Guangdong University of Technology
Course: Microelectronics and Solid State Electronics
Keywords: ZnO NaCo2O4 Hot-sintering First-principles analysis
CLC: TN377
Type: Master's thesis
Year: 2011
Downloads: 55
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Abstract


With the increasing of energy crisis and Global Warming, The application of thermoelectric power generation in waste heat utilization has caused for c oncern again, the design and preparation of high temperature electrode is one of the difficulties and focus in research of Temperature power generation tec hnology. On this basis,Theory、design and preparation of High-temperature electrode of waste heat thermoelectric power generation was researched.This paper briefly reviews the status of Oxide Thermoelectric Materials. T he main factors affect thermoelectric properties and ways to improve the ther moelectric properties of materials introduced; basic principles of thermal powe r generation devices, metal semiconductor contact theory and the welding pro cess discussed too.The preparation of ZnO substrate、Principles and Methods of performance test discussed. On this basis above, a new preparation process of N- type Zn O substrate:combined sintering process (hot-pressing+sintering) was offered.The appropriate complex sintering process parameters identified by experimen t. Experimental results show that the composite sintering process is feasible a nd the ZnO bulk materials with a certain structural strength and good thermal properties can be successfully prepared by composite sintering process, it hel p to reduce the thermal conductivity of the materials, thereby enhancing the t hermoelectric properties.Theoretical Analysis and preparation Technology of high-temperature electr odes were researched in the paper. N-type ZnO-based high-temperature electro de with Ag alloy as the electrode material successfully prepared by burn-osm osis, The prepared electrode with good electrical properties and good adhesi on and well ohm contact. The appropriate preparation of high-temperature ele ctrode was determine by Sintering and annealing experiment. In the fifth chapter, the paper briefly summarizes theoretical model for the analysis of first principles of NaCo2O4 electronic structure and reasons for s elect the CASTEP software package as computational tools.theoretical model of ideal and doped (Ca-doped and doped Ni) NaCo2O4 was Build. By GGA exchange-correlation approximation used, to Optimization of the crystal struct ure model firstly, then on this basis the ideal and doped (Ca-doped and dope d Ni) NaCo2O4 crystal band structure, total density of states and partial densi ty of states were calculated. The results showed that NaCo2O4 has electronic state structure of a typical semiconductor characteristic, has a lower energy g ap. Its conductivity comes mainly from Co-3dand O-2p orbital, Conduction ba nd mainly composed by Co-3d and O-2p, the valence band mainly constituted by the Co-3d.The high Co-3d density of states concentrated near the Fermi 1 evel, not only to increase the carrier concentration, but also to increased phon on. Thus, by means of doping change the occupy state of Co atoms, change it’s density of state near the Fermi level; the pyroelectric coefficient of NaCo 2O4 can be increased. Na were replaced by Ca, Ni substituted Co-bit, After Na substituted by Ca density of states Remained the same as Na, has small contribution in Conduction band and valence band, Distributed over a wide ar ea, will not bring improvement of conductivity. Ni substituted Co, electronic structure remains semiconductor structure, Ni mainly contribute atomic energy near the Fermi level, increase material’s carrier concentration, Help to impro ve the conductivity of materials. Should be primarily through the the way of change the occupy state of Co atoms, change density of states near fermi le vel to increase the pyroelectric coefficient of NaCo2O4.This conclusion provid es has a guiding role in NaCo2O4’s modification of the doping.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Semiconductor technology > Thermoelectric devices,thermistor > Temperature difference between electrical
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