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Doped perovskite manganese oxide thermoelectric properties of

Author: ZhangXinQuan
Tutor: LiZhuangZhi
School: Hebei Normal
Course: Condensed Matter Physics
Keywords: Sol - gel method Thermoelectric materials Seebeck coefficient Conductivity Thermal conductivity ZT
CLC: TB34
Type: Master's thesis
Year: 2011
Downloads: 38
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Abstract


Thermoelectric material because of its power (Seebeck effect) and cooling (Peltier effect) in the application, causing widespread interest of researchers. Non-perovskite manganese oxides cobalt oxide thermoelectric materials represents an important research direction. In this thesis, the sol - gel method with different doping concentrations of single perovskite manganite La 0.6 Sr 0.4-x K x MnO 3 , La 0.67 Sr 0.33-x Ag x MnO 3 < / sub> and double perovskite La 1 Sr 2-x Ag x MnO 7 polycrystalline powder , and under a pressure of 12 MPa in the polycrystalline powder is pressed into tablets, and then high-temperature calcination bulk samples to be tested. By X-ray diffraction (XRD) analysis phase composition of the samples were analyzed in detail, and through 10 4 00 K for physical performance measurement, systems of different ion doping on the resistivity of the sample , thermal conductivity, Seebeck coefficient and figure of merit ZT and other effects, by careful analysis of the test data, explored temperature range of samples with different conduction mechanism, and the two-phase model to explain the use of different doping Seebeck coefficient of the sample affected. The main results of this paper are as follows: 1. Using sol - gel method single perovskite manganite La 0.6 Sr 0.4-x K x MnO 3 , La 0.67 Sr 0.33-x Ag x MnO 3 and double perovskite La 1 Sr 2-x Ag x MnO 7 polycrystalline powder, XRD analysis for the composite sample multi-phase composition. Physical analysis showed that the samples conductive mechanism and temperature on the Seebeck coefficient of the sample are in line with the two-phase model. (2) the effects of different ions doped samples in 10 4 00 K thermoelectric properties, found that by suitable doping, the sample figure of merit ZT have been improved. Among them, the sample La 0.6 Sr 0.2 K 0.2 MnO 3 at 160 K can be achieved when the maximum value of 2.36 × ZT 10 -5 , sample La 0.67 Sr 0.13 Ag 0.2 MnO 3 at 151 K, a maximum of 1.41 × 10 -4 , than the majority of the undoped sample increased three orders of magnitude sample LaSr 1.9 Ag 0.1 Mn < sub> 2 O 7 sample at 391 K when the figure of merit reached 1.56 × 10 -5 , than the undoped samples adjusted figure of merit an order of magnitude higher. 3 measurements found, a Seebeck coefficient of the sample temperature to a low temperature, from negative to positive after the process, and at 300 K transition temperatures are nearby. At high temperatures, Seebeck coefficient by the small polaron; in the low temperature region, seebeck coefficients are electronic - phonon contribution. 4 elemental Ag ratio of the conductivity of pure perovskite larger, through the incorporation of high concentrations of metals Ag, part of the metal particles dispersed in the perovskite matrix, the special interface effects and to increase sample percolation effects conductivity. In addition, a small amount of Ag as a heavy ions into the perovskite structure will reduce the thermal conductivity of the sample. The results show that the conductivity of the composite increases with the amount of Ag first increases and then decreases, as compared with the undoped sample was significantly enhanced when the Ag content is 0.05, the conductivity maximum of 21505.37 S · m -1 , than the undoped Ag-La 0.67 Sr 0.33 MnO 3 increased by about 16 times. When the amount of Ag is small, a small amount of Ag ions into the lattice structure, Ag doped with increased concentration of carriers, carriers corresponding increase in thermal conductivity, Ag further increased, a part of Ag ions into the lattice structure in, Ag Sr high quality than the number of Ag on the structure of Sr-bit replacement will reduce the lattice vibrations caused by the lattice thermal conductivity. The research on the development of oxide thermoelectric material has a certain practical value and significance. Future studies, optimum performance can be doped with manganese perovskite oxides prepared by pulse laser deposition epitaxial films, exploring a high thermoelectric properties oxide film.

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