Ca_3Co_2O_6块体的放电等离子烧结及热电性能研究

Research on Spark Plasma Sintering and Thermoelectric Properties of Ca_3Co_2O_6 Bulk

采用短时固相反应和放电等离子烧结（SR-SPS）方法，制备了单相多晶Ca3Co2O6陶瓷块，系统研究了制备条件及烧结工艺对Ca3Co2O6陶瓷块显微结构及热电性能的影响。研究表明，950℃下固相反应2h即能得到单相树枝状，尺寸约1～3μm的Ca3Co2O6粉末，延长焙烧时间虽然对物相影响不大，但会引起粉末颗粒长大，不利于SPS烧结；SPS烧结温度强烈影响着Ca3Co2O6陶瓷块的制备，本实验范围内，Ca3Co2O6陶瓷块体的最佳制备条件为950℃固相反应2h，SPS900℃保温5min，此时Ca3Co2O6陶瓷块具有P型半导体特性，电阻率ρ随温度的升高急剧下降，然后趋于平缓（高于600℃）；Seebeck系数S随温度（100℃以上）升高稍有下降，热导率Ⅳ表现为先下降后增加，在500℃时仅为1．73W·m^-1·K^-1综合电性能与热性能结果，其无量纲因子ZT随 温度升高呈上升趋势，在本实验范围内，于700℃下达到最高值0．02。

Short-time solid reaction and spark plasma sintering method （SR-SPS） was used to prepare single-phase polycrystalline Ca3Co206 ceramic bulk, and effects of preparation condition and sintering technology were investigated in detail. Single-phase dendritic Ca3Co2O6 powders with grain size of about 1 - 3μm were obtained under 950 for 2 h by, solid-state reaction process, and prolonged reaction time could hardly influence phase structure, but it could make grain size growth, which is harmful for SPS sintering. Temperature of SPS strongly affects the preparation of Ca3Co2O6 ceramic bulk. In our experimental range, the best condition for Ca3Co206 ceramic bulk is to react under 950℃ for 2 h, and then sinter under 900℃ for 5 min by SPS. The bulk obtained by above technology shows character of p-type semiconductor, electrical resistivity ρ decrease sharply and then slightly, Seebeck coefficient S reduces, thermal conductivity r decreas- es and then increases with increasing temperature, the minimum value of r is 1.73 W- m- i. K^-1l at 500 ℃. As a result, the figureless factor of merit ZT shows in- creasing trend and the maximum value of ZT reaches 0.02 at 700 ℃ in our experimental range.