材料期刊网

本研究发展了一种用于制备氧化物热电材料γ-NaxCoO2粉体的化学合成方法——聚丙烯酸钠(PAAS)凝胶法.主要研究了PAAS/Co2+摩尔比、原料浓度和煅烧温度对产物相组成及微观形态的影响规律,探讨了物相形成机制,同时用该方法结合SPS制备了不同Na离子浓度的NaxCoO2多晶样品,并对其热电性能进行了表征.结果表明,PAAS/Co2+摩尔比对产物相组成产生了显著影响,随着PAAS/Co2+摩尔比的增加,样品的相组成由Co3O4相向单相γ-NaxCoO2转变,合适的PAAS/Co2+摩尔比为0.8~1.1.而反应原料浓度对产物相组成的影响存在一个临界值(0.025 mol/L),大于临界值抑制单相形成,小于临界值促进单相形成.煅烧温度的升高有助于γ-NaxCoO2单相的形成,800℃煅烧得到γ-NaxCoO2单相,晶粒形态呈片状,平均厚度约200 nm,片状方向的尺寸在1~4μm之间.随着Na含量的增加,样品的Seebeck系数增大,电导率增加,热导率降低,最终导致ZT值大幅增加.

Chemical synthesis method of sodium polyacrylate (PAAS) gel method was used to prepareγ-NaxCoO2 powders. The effects of PAAS/Co2+molar ratio, concentration of raw materials and calcination temperatures on the phase composition and microstructure of product were studied. NaxCoO2 polycrystalline samples with different Na+ concentrations were synthesized by the above method, and the thermoelectric properties were characterized. The results showed that the PAAS/Co2+molar ratiogreatly affected the phase composition. With the increase of PAAS/Co2+molar ratio, the phase composition of sample was transformed from Co3O4 toγ-NaxCoO2. The proper molar ratio of PAAS/Co2+ to obtainγ-NaxCoO2 single phase is 0.8. the phase composition of sample will change slightly with different concentrations of raw materials.γ-NaxCoO2 single phase was formed at low concentra-tion of raw materials (below 0.025 mol/L), however, when the concentration exceeded 0.025 mol/L, the second phase was formed. The formation ofγ-NaxCoO2 single phase was promoted with the increase of calcination tem-perature. Theγ-NaxCoO2 powders calcined at 800℃ were plate-like particles with about 200 nm in thickness and about 1-4μm in width along the plane direction. With the increase of Na content in samples,σ value and S value were increased whileκ value was decreased, leading to a significant increase inZT value.