Evaluation of the High-Temperature/High-Efficiency Thermoelectric Device Consisted of Refractory Semiconducting Ceramics

本文对难熔半导体材料多孔SiC和碳化硼的高温热电转换效率进行了研究，得到了以下结果：首先，多孔SiC采用实心和空心SiC细颗粒为原料，通过常规烧结工艺，获得了具有不同孔隙率和双峰粒度分布的微结构;热电性能的测试表明，多孔SiC单晶基体上分布着非常细的孔，具有很高的热电转换性能。其次，对于碳化硼，通过改变CVD条件，制备了组成不变但晶粒尺寸和晶轴取向度不同的厚膜陶瓷，研究了它们的热电特性。结果发现，具有随机晶轴取向的细晶粒多晶体应提供高的能量转换效率。

Investigations on the high-temperature thermoelectric conversion efficiency of refractory semiconductors, namely porous SiC and boron carbide were carried out and the following results were obtained.First, for porous SiC,microstructures with various porosities and bimodal grain-size distributions were achieved by normal sintering process employing both solid and hollow fine particles of SiC as starting materials. Measurement of thermoelectric properties of the resultant materials has shown that porous SiC of its single-crystalline matrix dispersed with very fine pores would give large figures of merit for thermoelectric conversion.Second, for boron carbide, thick-film ceramics with constant composition yet with different grain sizes and different degrees of crystal axis orientation were fabricated by varying the CVD conditions, and their thermoelectric characteristics were investigated. It was found that fine-grained polycrystals with random crystal-axis orientation should give high energy conversion efficiency.