纳米SiO_2包覆提高填充方钴矿热电材料热稳定性

Enhancement of Thermal Stability of Filled Skutterudite Thermoelectric Materials through Nano-SiO_2 Coating

采用熔融结合放电等离子体烧结制备了单相Ba0.3In0.2Ni0.05Co3.95Sb12块体材料,并用湿化学包覆处理方法制备了纳米SiO2包覆的Ba0.3In0.2Ni0.05Co3.95Sb12/SiO2纳米复合材料,重点研究了两种（Ba,In）双原子填充方钴矿基块体材料在300-723-300K范围热循环2000次过程中其显微结构、化学成分和热电性能的演变特征.结果发现,纳米SiO2包覆可以显著提高（Ba,In）双原子填充方钴矿块体材料的热稳定性,单相Ba0.3In0.2Ni0.05Co3.95Sb12块体材料晶界处的显微结构和化学成分发生显著变化,Ba0.3In0.2Ni0.05Co3.95Sb12/SiO2纳米复合材料几乎没有影响,纳米SiO2起着稳定晶界和抑制晶内元素扩散与挥发的作用.热循环过程中,两种材料在300和500K时的综合热电性能ZT值相近,变化很小;800K时,单相块体材料的ZT值呈逐渐降低趋势,纳米复合材料由于受热导率的复杂变化影响其ZT值,随淬火次数增加而逐渐增大,淬火1800次时ZT值达到1.12,甚至高于未淬火的Ba0.3In0.2Co3.95Ni0.05Sb12/SiO2纳米复合材料（1.08）和淬火1800次后的单相Ba0.3In0.2Co3.95Ni0.05Sb12块体材料（1.10）的ZT值.

Single-phase Ba0.3In0.2Ni0.05Co3.95Sb12 bulk materials were synthesized by melting and spark plasma sintering（SPS） methods.Ba0.3In0.2Ni0.05Co3.95Sb12/SiO2 nanocomposite material with nano-SiO2 coating was prepared by wet chemical coating processing.Emphases were given on the evolution of microstructure,chemical composition,and thermoelectric properties of two kinds of（Ba,In） double-atom filled skutterudite based bulk materials during periodic thermal cycling 2000 times in the range of 300-723-300 K.It was found that the thermal stability of（Ba,In） double-atom filled skutterudite was remarkably improved after nano-SiO2 coated.The microstructure and chemical composition along the grain boundaries of single-phase Ba0.3In0.2Ni0.05Co3.95Sb12 bulk material obviously changed,while the thermal cycling had no effect on Ba0.3In0.2Ni0.05Co3.95Sb12/SiO2 nanocomposite.Thus the nano-SiO2 stabilized the grain boundary and prevented the elements diffusing and volatilizing from intra-grain.The ZT values of two kinds of materials were very close and kept unchanged at 300 K and 500 K during the thermal cycling.The ZT values of single-phase bulk materials gradually decreased at 800 K.However,the ZT values of nanocomposite mainly depended on the complex changes in thermal conductivity and increased with prolonging of quenching time,then reached 1.12 at 800 K after quenching for 1800 times,which was even higher than those of unquenched Ba0.3In0.2Co3.95Ni0.05Sb12/SiO2 nanocomposite（ZT=1.08） and single-phase Ba0.3In0.2Co3.95Ni0.05Sb12 bulk material（ZT=1.10） quenched for 1800 times.