Ca-Co-O热电材料微波合成及其性能优化

发布时间：2018-09-11 20:54

【摘要】：本文以Ca_9Co_(12)O_(28)热电材料为研究对象,分别通过微波烧结,掺杂与金属复合等手段,改变热电材料的晶界密度、载流子浓度和声子散射中心数量,从而对其性能进行优化。实验研究成果如下:第一,采用微波烧结制备Ca_9Co_(12)O_(28)热电材料,通过微波烧结过程中的晶粒细化效应,在本体材料中引入大量晶界,使得声子的晶界散射几率增大,降低了热导率,最终实现热电优值的提高。实验结果表明经微波烧结的样品结构更加致密,晶粒尺寸更小,平均尺寸在1um以下,其热电优值在500oC下达到0.042。第二,采用溶胶-凝胶法制备(Ca_(3-x)La_x)3Co_(12)O_(28)(x=0,0.05,0.1,0.15,0.2,0.3)热电材料,通过在本体材料中掺杂稀土元素La,改变材料载流子浓度,从而引起热电优值的提高。实验发现,(Ca2.9La0.1)3Co12O28的热电优值最高,在500oC时达到0.068,比未掺杂的Ca_9Co_(12)O_(28)提高约61.9%。表明掺杂稀土元素能有效提高材料的热电性能。第三,采用化学溶液浸润法制备(Ca_9Co_(12)O_(28))1-x Agx(x=0,0.005,0.01,0.015,0.02)热电复合材料,使Ag均匀地分散在Ca-Co-O氧化物晶粒之间,形成有效的声子散射中心,降低材料热导率,提高其热电优值。通过性能测试在Ag复合比例为x=0.015的样品ZT值最高,在500oC达到0.07,比纯相提高约66.7%。总之,采用掺杂La方法可以改变材料载流子浓度,提高材料热电性能;采用微波技术可以提高材料内部晶界密度,降低了材料热导系数;采用Ag复合方法在材料内部产生大量声子散射中心,也可以有效降低材料热导系数。从而为进一步优化热电材料性能打下基础。
[Abstract]:In this paper, Ca_9Co_ _ (12) O _ (28) thermoelectric materials are studied. By means of microwave sintering, doping and metal recombination, the grain boundary density, carrier concentration and the number of phonon scattering centers of thermoelectric materials are changed to optimize their properties. The experimental results are as follows: first, Ca_9Co_ _ (12) O _ (28) thermoelectric materials are prepared by microwave sintering. Through the grain refinement effect in the process of microwave sintering, a large number of grain boundaries are introduced into bulk materials, which increases the probability of phonon grain boundary scattering and reduces the thermal conductivity. Finally, the improvement of the excellent value of thermoelectricity is realized. The experimental results show that the microstructure of the samples sintered by microwave is denser, the grain size is smaller, the average size is below 1um, and the thermoelectric excellent value reaches 0.042 in 500oC. Secondly, (Ca_ (3-x) La_x) 3Co12 O28 (x00.05) 0.15 0.2ng) thermoelectric material was prepared by sol-gel method. The carrier concentration of the material was changed by doping rare earth element La, in bulk material, which resulted in the increase of thermoelectric excellent value. It is found that the thermoelectric excellent value of (Ca2.9La0.1) 3Co12O28 is the highest, reaching 0.068 at 500oC, which is 61.9% higher than that of undoped Ca_9Co_ _ (12) O _ (28). The results show that doped rare earth elements can effectively improve the thermoelectric properties of the materials. Thirdly, (Ca_9Co_ _ (12) O _ (28) 1-x Agx (XO _ 0. 005 ~ 0. 01 ~ 0. 015 ~ 0. 02) thermoelectric composites were prepared by chemical solution infiltration method. Ag was uniformly dispersed among Ca-Co-O oxide grains, forming effective phonon scattering centers, reducing the thermal conductivity of the materials and improving their thermoelectric excellence. The ZT value of the sample with Ag composite ratio of xn0. 015 is the highest, and the value of 500oC is 0. 07, which is about 66. 7% higher than that of pure phase. In a word, the carrier concentration of the material can be changed by doping La method, and the thermoelectric properties of the material can be improved, and the grain boundary density can be increased by microwave technology, and the thermal conductivity of the material can be reduced. A large number of phonon scattering centers are produced in the material by Ag composite method, which can also effectively reduce the thermal conductivity of the material. Thus lay the foundation for further optimizing the properties of thermoelectric materials.
【学位授予单位】：郑州航空工业管理学院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB34

【参考文献】