【作者】 戚德奎；

【导师】 唐新峰；

【作者基本信息】 武汉理工大学 ， 材料学， 2010， 硕士

【摘要】 P型β-Zn4Sb3材料由于具有极低的热导率,因而具有优越的热电性能,在670K时其热电优值ZT可达1.3,是目前极具应用前景的中温热电材料。但由于Zn4Sb3体系本身的材料脆性和在相转变过程中由于热膨胀系数变化而产生的微裂纹,导致材料具有较差的力学性能和可加工性,大大限制了β-Zn4Sb3材料的商业化应用。因此探索新的制备工艺,制备出不仅具有优良热电性能而且具有较高力学强度的块体Zn4Sb3材料是该体系的研究主要任务。本论文以p型β-Zn4Sb3基化合物为研究对象,通过结构低维化结合第二相和掺杂手段来改善p型β-Zn4Sb3化合物的热电、力学性能。探索了熔体旋甩(MS)结合放电等离子烧结(SPS)技术制备β-Zn4Sb3化合物的可能性,揭示了MS-SPS过程中材料的相转变过程及微结构的形成规律,研究了MS工艺对材料热电、力学性能的影响规律；在此基础上,通过原位生成Zn第二相和Cd掺杂的方法进一步提高了β-Zn4Sb3化合物的热电、力学性能。主要研究内容和研究结果如下：探索了熔体旋甩快速凝固(MS)结合放电等离子快速烧结(SPS)制备具有纳米结构β-Zn4Sb3块体材料的可能性。直接以熔融法制备的锭块为母合金,单相的母合金经MS处理后得到含有Zn3Sb2、ZnSb、Zn4Sb3多相组成的薄带产物；MS过程中铜辊转速对薄带产物的微结构有显著影响,铜辊转速越高,得到的薄带产物晶粒更加细小,成分分布更加均匀；经过SPS烧结后,多相的薄带产物在短时间的SPS烧结过程中转变为单相的β-Zn4Sb3致密化合物,而且薄带中精细的纳米结构被保留在SPS烧结后的块体中,形成具有多尺度纳米结构的块体材料；相比于直接熔融法制备的β-Zn4Sb3化合物,MS-SPS样品的Seebeck系数显著增加,热导率大幅度降低,ZT值得到了大幅的提高,所有MS-SPS样品的ZT值均达到1.0左右；另外,MS-SPS样品与熔融法制备的样品相比,力学强度也得到大幅提高。通过调节Zn的原始组成,研究了第二相Zn和ZnSb对MS-SPS技术制备β-Zn4+xSb3化合物热电、力学性能的影响。原始组成Zn微量过量或不过量时,由于在制备过程中Zn的挥发会导致最终块体材料中产生ZnSb第二相,而ZnSb第二相会严重劣化材料的热电性能；而适度过量的Zn不仅可以有效弥补在制备过程中Zn的挥发,且随着Zn过量程度的增加会使块体材料中产生弥散分布的纳米Zn第二相,这种纳米金属Zn第二相对材料的热电、力学性能有良好的作用；金属第二相Zn有效的提高了材料的电导率,优化了材料的电热输运特性,因此提高了材料的热电优值ZT,其中,Zn4.32Sb3样品具有最好的热电优值ZT,在700K时达到了1.13；另外,金属相的Zn第二相可以有效地改善材料的力学性能,主要是由于金属第二相的塑性变形可以吸收弹性应变能的释放量,改善脆性材料的强度。采用熔融法传统工艺及MS-SPS技术制备了Cd掺杂的β-Zn4Sb3化合物。研究表明熔融法制备的Zn4-xCdxSb3化合物中当x<0.15时可以得到单相的β-Zn4Sb3化合物,当x=0.15时,产物的XRD图谱中出现Cd的特征峰,说明Cd在β-Zn4Sb3化合物中的固溶极限x<0.15；通过Cd掺杂调节了β-Zn4Sb3化合物的电热输运特性,随着Zn4-xCdxSb3化合物中Cd掺杂量x的增加,样品的载流子浓度降低,而载流子迁移率变化不大；x<0.15时,随着Cd含量x的增加,材料的电导率略有降低,Seebeck系数增加,同时样品的热导率随着Cd掺杂量x的增加而显著降低,因此最终材料的热电优值ZT得到了提高；由于熔融法制备的Zn4-xCdxSb3化合物仍具有较高的热导率,因此我们通过MS-SPS技术制备了Zn3.95Cd0.05Sb3样品,MS工艺的引入使块体材料具有低维结构,相比与熔融法制备的该组成样品,热导率大幅降低,因此MS-SPS法制备的Zn3.95Cd0.05SB3样品具有较高的热电优值ZT,在700K时达到了1.20。更多还原

【Abstract】 P-typeβ-Zn4Sb3 compound has become one of the most promising thermoelectric (TE) materials because it has exceptional thermoelectric properties in the intermediate temperature range. The maximum ZT value reaches 1.3 at 670K because of its extremely low thermal conductivity originated from its complex crystal structure. While the fragility and the microcracks result from the phase transition greatly decrease the mechanical property and process ability, which limits its commercial application. Therefore, to fabricateβ-Zn4Sb3 bulk material with not only high thermoelectric performance but also high mechanical durability is of vital significance.In this research, we focus on p-typeβ-Zn4Sb3 compound. The thermoelectric properties and mechanical properties are expected to be improved by obtaining low-dimensional structure combining doping or producing second phase material methods. We explore the feasibility of preparing the nanostructuredβ-Zn4Sb3 bulk material by combining melt-spinning (MS) with spark plasma sintering (SPS) technique, study the phase transform and the microstructure formation during the MS processes, and the influences of MS process on TE properties and mechanical properties are investigated. Base on the above research works, we study the influences of second phase and doping element on TE properties and mechanical properties for MS-SPS materials. The main obtained results are as follows:We developed a novel synthesis technique that is MS-SPS method to quick prepare nano-structured p-typeβ-Zn4Sb3 bulk material. The ingots prepared by melting method are used as starting materials. After MS treatment, the single phase ingot transforms into multi-phase ribbons containing not only Zn4Sb3 but also Zn3Sb2 and ZnSb. The process parameter of MS process (linear speed of the spinning cooper wheel) has great influences on the microstructure of MS ribbons. With higher linear speed of the spinning cooper wheel, we can get ribbons with smaller grain size. After SPS treatment, the multi-phase ribbons can be transformed to single-phaseβ-Zn4Sb3 in a very short time, and the nanostructure induced by melt spinning technique can be preserved after SPS processing. Compared with the sample prepared by the traditional melting method (M-ingot), the Seebeck coefficient of the MS-SPS samples increases significantly and the thermal conductivity decreases remarkably, which leads to a great improvement in the thermoelectric figure of merit (ZT). Moreover, the mechanical strength of the MS-SPS samples has great improvement compared with M-ingot sample.By adjusting the amount of Zn, we studied the influences of Zn and ZnSb second phase on TE properties and mechanical properties of MS-SPSβ-Zn4+xSb3 compounds. With a little Zn excess (x<0.08), we can get (3-Zn4Sb3 bulk material containing ZnSb second phase because of Zn volatilization during preparation. And ZnSb phase has bad influence on the TE performance ofβ-Zn4Sb3 material. While moderately superfluous Zn improves the electrical transport properties significantly. Excess Zn may lead to nano-scalled second Zn phase dispersed on the boundary which optimizes the electrical and thermal transport properties, and leads to an improvement on the ZT value. The ZT value of Zn4.32Sb3 sample reaches 1.13 at 700K. Moreover, the Zn second phase has good influence on the mechanical properties. With the increase of Zn content, the mechanical properties of the MS-SPS samples increase greatly.A range of Zn4-xCdxSb3 compounds are synthesized using a traditional melting method and MS-SPS method. The results show that we can get single phase Zn4Sb3 material when x<0.15, and we can find Cd peaks in XRD patterns of Zn3.85Cd0.05Sb3. It means that the solid solubility limit of Cd in the Zn-Sb system is x<0.15. With increasing Cd content x, the room-temperature carrier concentration of Zn4-xCdxSb3 compounds decreases, while the carrier mobility is nearly unchanged. For Zn4-xCdxSb3 compounds (x< 0.15), the electrical conductivity and thermal conductivity decrease with increasing x, while the Seebeck coefficient raises largely. So this leads to a great improvement in the ZT value, the maximum ZT value of 1.05 is obtained at 700K for Zn3.90Cd0.10Sb3 sample prepared by melting method. Because of high thermal conductivity, the ZT values of the Zn4-xCdxSb3 samples prepared by melting method are rather low. So we adopt MS-SPS method to prepare the Zn3.95Cd0.05Sb3 sample with lower thermal conductivity. The results show that the MS-SPS Zn3.95Cd0.05Sb3 sample has fine nanostructure and so has very low thermal conductivity. Compared with the sample prepared by melting method, the ZT value of MS-SPS Zn3.95Cd0.05Sb3 sample is largely improved, reaching 1.20 at 700K.更多还原