【作者】 罗沛兰；

【导师】 李克； 赵新兵；

【作者基本信息】 南昌大学 ， 材料加工工程， 2009， 硕士

【摘要】 热电材料是一种能够实现电能与热能之间直接转换的半导体功能材料。由热电材料制作的温差发电和制冷器件具有无污染、无噪声、易于维护、安全可靠等优点,在工业余热发电、航天、微电子及制冷等领域具有广泛的应用。方钴矿化合物是一种新型的中温区热电材料,其中填充方钴矿化合物因其同时具有晶体的良好导电性能和玻璃的低热导率被认为是一种典型的“电子晶体-声子玻璃”材料。制备多元的填充方钴矿材料可以优化材料成分,提高材料的热电性能。本文采用真空熔炼-退火合成方法,以Co、Sb、Ni、Yb、La、Te等单质为原料制备了方钴矿化合物。应用XRD、SEM等手段对粉末、热压试样进行了物相成分和微观形貌的分析。对熔炼试样粉末采用真空热压技术进行热压,测试热电性能。主要取得以下研究成果:1.制备了La、Yb、Ce单填充和La-Ca、La-Yb双填充方钴矿化合物,并研究了它们的热电性能。研究发现不管是单填充还是双填充都能够显著的降低方钴矿材料的热导率,但采用La-Yb双填充改善电学性能效果不佳。其中La_0.5Co₄Sb₁₂、Yb_0.2Co₄Sb₁₂、Ce_0.2Co₄Sb₁₂和La_0.4Ca_0.1CO₄Sb₁₂的最大ZT分别达到了0.69（773K）、1.24（773K）、0.55（723K）和0.74（735K）。在提高方钴矿热电性能方面,重稀土元素Yb优于轻稀土元素La和Ce,稀土-碱土双填充方钴矿优于这两种元素的单填充方钴矿。2.采用熔炼-退火方法制备了La、Ni共掺方钴矿热电材料La_0.3Co_4-xNi_xSb₁₂（x=0,0.1,0.5,0.75,1）。研究发现,Ni的固溶度在0.5到0.75之间,La_0.3Co_4-xNi_xSb₁₂显n型。随着x值的增大,Seebeek系数绝对值总体呈下降趋势,而电导率和热导率则增加。La_0.3Co_3.9Ni_0.1Sb₁₂功率因子和ZT值分别达到最佳:功率因子σ·α_max²=3.97×10^-3Wm^-1K^-2（520K）,ZT_max=0.64（773K）。3.设计了La_0.5Co₄Sb_11.9Te_0.1:Sb₂Te₃:Bi₂Te₃=1:0.05:0.04（摩尔比）、La_0.2Yb_0.2Co₄Sb_11.8Te_0.2和La_0.1Yb_0.2Ca_0.1Co_3.9Ni_0.1Sb_11.9Te_0.1三种成分。发现少量Te和Bi掺杂到La_0.5Co₄Sb₁₂中可以减小最大ZT值的所处温度。由于Te元素在Sb位的固溶,化合物La_0.2Yb_0.2Co₄Sb_11.8Te_0.2的ZT值在773K时达到了1,比La_0.2Yb_0.2Co₄Sb₁₂提高约233%。实验结果表明,元素Te掺杂方钴矿可以提高方钴矿材料的热电性能,稀土元素双填充与少量Te元素掺杂结合可以有效加强对声子的散射,大幅度地降低声子热导率。La_0.1Yb_0.2Ca_0.1Co_3.9Ni_0.1Sb_11.9Te_0.1的最大ZT值为0.6（708K）。更多还原

【Abstract】 Thermoelectric（TE） materials are semiconducting functional materials,which can convert heat energy directly to electricity or reversely.TE power generators and cooling devices have been extensively applied in waste heat harvesting,space flight, microeleetronic cooling with the merit of pollution-free,noiseless,easy-maintenance and reliability.Skutterudite-based compounds considered to be promising novel TE materials in middle temperature range.Filled skutterudites are suggested as the "phonon-glass/electron-crystal" materials with the good electrical transport properties of a crystal but the poor heat conduction characteristics of a glass.The preparation of multicomponent alloy such as filled skutterudites can optimize material compositions and improve thermoelectric properties.In this work,skutterudites are prepared by vacuum melting and annealing from pure Co,Sb,Ni,Yb,La,Te and other alloying or doping elements,and also by vacuum hot pressing from the alloy powders.The compositions and microstructures of the powders and the hot pressed bulk skutterudites were investigated by x-ray diffraction（XRD） and scanning electron microscopy（SEM）.Transport properties of the hot pressed bulk samples were measured.The main results of the present work are listed as follows.1.The single filled（La,Yb,Ce） and double filled（La-Ca,La-Yb） skutterudites were prepared and their thermoelectric properties were studied.It was shown that the thermal conductivity is greatly reduced by forming single filled and double filled cobalt antimonide,but the thermoelectric properties for the La-Yb filled skutterudites, La_xYb_0.2Co₄Sb₁₂,were not so good.The highest ZT values for the La_0.5Co₄Sb₁₂, Yb_0.2Co₄Sb₁₂,Ce_0.2Co₄Sb₁₂,La_0.4Ca_0.1Co₄Sb₁₂ were 0.69（773K）,1.24（773K）,0.55 （723K）,and 0.74（735K） respectively.It was found that the heavy RE（rare earth） element Yb was better than the light ones,La and Ce,in both electrical conductivity and thermal conductivity,and similiarly RE-AE was better than their separate element.2.Thermoelectric（TE） materials La_0.3Co_4-xNi_xSb₁₂（x=0,0.1,0.5,0.75,1） were prepared by melt-annealing method.The solid solubility limit of Ni in La-filled CoSb₃ is between 0.5 and 0.75 when the filling rate of La is 0.3.Transport properties measurements indicate that all these La_0.3Co_4-xNi_xSb₁₂ samples are n-type.The absolute Seebeck coefficient values decrease with the increasing of the value of x, however,the values of electrical conductivity and thermal conductivity increase with the addition of Ni.As a result,the La_0.3Co_3.9Ni_0.1Sb₁₂ Skutterudites exhibit a maximum power factor of 3.97×10^-3Wm^-1K^-2 at 520K and a maximum ZT value of 0.64 at 773K.3.Three samples La_0.5Co₄Sb_11.9Te_0.1:Sb₂Te₃:Bi₂Te₃=1:0.05:0.04（mall rate）, La_0.2Yb_0.2Co₄Sb_11.8Te_0.2 and La_0.1Yb_0.2Ca_0.1Co_3.9Ni_0.1Sb_11.9Te_0.1 were designed and prepared in this work.It was found that a small quantity of Te and Bi could help to deduce the temperature at the highest ZT value in the composite La_0.5Co₄Sb₁₂.Due to Te subsititution for Sb,a ZT value～1 at 773K for La_0.2Yb_0.2Co₄Sb_11.8Te_0.2,which is 233%higher than that of La_0.2Yb_0.2Co₄Sb₁₂.The thermoelectric properties could be further improved by Te doping.Combination double RE filling with a small quantity of Te doping could effectively increase the scattering of phonons to greatly decrease the thermal conductivity.The highest ZT value of 0.6 is obtained for La_0.1Yb_0.2Ca_0.1 Co_3.9Ni_0.1Sb_11.9Te_0.1 at 708K.更多还原