【作者】 周龙；

【导师】 唐新峰；

【作者基本信息】 武汉理工大学 ， 材料学， 2011， 硕士

【摘要】 热电转换材料作为一种环境友好的新能源材料,被认为是21世纪非常有竞争力的能源替代介质。方钴矿化合物由于具有较大的载流子迁移率以及较大的Seebeck系数,被认为是非常具有应用前景的中温热电材料。但是由于其相对较高的热导率使其热电性能指数ZT值处于较低的水平,严重限制了其商业化应用。本论文以n型填充式CoSb3基方钴矿为研究主体,尝试合成得到具有原位析出纳米第二相的复合热电材料,期望通过调控电性能的同时降低材料的晶格热导率,从而提高材料的热电优值。以In, Ce为掺杂元素,阐明不同掺杂元素在CoSb3化合物中的存在形式及其对微结构和热电性能的影响规律。主要研究内容和研究结果如下：以In掺杂n型CoSb3基方钴矿为研究对象,研究了In在填充式方钴矿的存在形式,纳米第二相InSb的稳定性以及InSb含量的变化对微结构及热电性能的影响规律。研究结果表明,In可以以填充形式存在于方钴矿结构中但是其填充形式存在是亚稳态的且在适当的外界条件下可以析出以更稳定的InSb化合物形式存在,但是In以填充原子存在时更能够优化化合物的热电性能。同时也推断在In填充量接近的情况下,InSb第二相能够在通过注入电子从而提高化合物的电性能的同时通过纳米分布对声子进行强烈的散射从而降低晶格热导率,提高材料的热电性能指数。研究结果还表明,随着In含量的增加,InSb含量的增多,室温下载流子浓度增大,电导率增大,Seebeck系数减小。InSb第二相在晶粒之间的晶界处的广泛分布大大降低了InxCo4Sb12(x=0.1-0.4)方钴矿化合物的晶格热导率,提高了热电性能。In0.35CO4sb12化合物在温度为800K时ZT值达到了1.16。另外将In0.35CO4sb12化合物,在400℃分别退火7天和14天。退火后样品晶粒尺寸较为均匀,且退火14天后的样品内由于亚稳态填充式In在高温驱使下从空洞中析出致使晶界处出现了更多絮状分布的InSb纳米第二相。在温度为730K左右时,退火14天后的样品出现了最大ZT值为1.22。在原位析出InSb纳米第二相的n型In填充式方钴矿的基础之上,进行Ce原子填充,形成了双原子填充式方钴矿,以期望对其电声输运特性进行调控,从而得到更为优化的热电性能。研究结果表明,Ce在方钴矿的填充上限为0.11左右,且超过填充上限的Ce在方钴矿中会形成CeSb第二相且分布在晶粒与晶粒之间的晶界处。Ce作为填充原子的引入,可以在提高化合物的电性能通过扰动降低化合物的晶格热导率,从而优化材料的热电性能,Ce0.15CO4sb12的样品在温度为800K时取得最大ZT值0.97。采用同样的方法合成了InxCe0.1Co4Sb12化合物,研究结果表明,当In的掺杂量超过0.2时,化合物中出现了原位析出的InSb纳米第二相以岛状形式分布在晶界处,且其含量随着In含量的增加而增大。相比于InxCo4Sb12化合物,InxCe0.1Co4Sb12化合物具有更高的功率因子以及更低的晶格热导率,说明Ce在InxCeo.1Co4Sb12化合物中确实能够在提高电性能的同时降低热导率,从而提高材料的ZT值,In0.25Ce0.lCo4Sb12化合物在800K取得最大ZT值1.25。更多还原

【Abstract】 Thermoelectric materials, environmentally friendly materials in the 21st century, are considered to be very competitive in the energy alternative media. Skutterudite (such as binary CoSb3 compound) compounds have become one of the most promising TE materials because of their higher carrier mobility and high Seebeck coefficient. However, the figure-of-merit ZT using to evaluate the performance of TE materials and conversion of thermo-electricity of binary skutterudites are not famous owing to its relatively large thermal conductivity, severely limiting its commercial application.In this research, we focus on the n-type filled CoSb3 compound, expecting to regulate and control the electrical properties while lowering the lattice thermal conductivity and thereby enhancing the figure-of-merit ZT by in situ formation method. In and Ce are used as the doping elements and the forms of existence and the effects on the microstructure and TE properties of the n-type filled CoSb3 compound of these doping elements are discussed. The main contents and findings of the research work above are as follows:We used In as the doping element and discussed the forms of existence of In, the stability of the nano phase InSb and the effects of In doping on the microstructure and thermoelectric properties in the CoSb3-based skutterudite. The results show that:In can fill the void in the structure of skutterudites but the filling-form is metastable and In can separate out from the void to form the nano second phase InSb compound. But In with filling-form are better able to optimize the thermoelectric properties of compounds. We find that the existence of nanostructured secondary phase InSb can increase the power factor, decrease the lattice thermal conductivity and therefore improve the thermoelectric properties of the compounds when the content of In with filling-form are close to each other. Wih regard to the InxCo4Sb12 compound, the highest thermoelectric figure of merit ZT=1.16 is achieved at 800 K in the In0.35Co4Sb12 compound, In addition, In0.35Co4Sb12 compounds were annealed respectively at 400℃for 7 days and 14 days. The grain size of annealed samples are more uniform and the content of secondary phase InSb of the sample annealed 14 days are more than the annealed-7 days sample because of the metastable state of filling-form In.Based on the in situ secondary phase InSb dispersed on the boundary in the n-type skutterudites compounds, we use In and Ce as the filling element to form the double-filled skutterudits, hoping to achieve more optimized thermoelectric properties. The results show that, the filling fraction limit of Ce in CexCo4Sb12 compounds is about 0.11 and CeSb is formed and dispersed in the grain boundaries when the content of Ce exceed its filling fraction limit. As the filling element, Ce can improve the electric properties, lower the lattice conductivity and therefor enhance the igure of merit ZT. Wih regard to the CexCo4Sb12 compound, the highest thermoelectric figure of merit ZT=0.97 is achieved at 800 K in the Ce0.15Co4Sb12 compound. Using the same method, InxCe0.1Co4Sb12 compounds were synthesized. We find that when the content of doping-In was more than 0.2 there was nano secondary phase InSb compound distributed on the boundaries with the islandstructure. Compared with the the InxCo4Sb12 compound, InxCe0.1Co4Sb12 compound have higher Power factor and lower lattice conductivity and more optimize thermoelectric properties. The highest thermoelectric figure of merit ZT=1.25 is achieved at 800 K in the In0.25Ce0.1oCo4Sb12 compound.更多还原