c轴择优Ca_3Co_4O_9多晶的热电性质及激光感生横向电压效应

采用传统固相反应法制备c轴择优的错层结构Ca3Co4O9多晶材料,用热重-差示扫描量热分析、X射线衍射、扫描电子显微镜和电阻率–温度曲线、热电势–温度曲线对样品进行了表征,探究了材料热电输运性质和激光感生横向电压(laser induced transverse voltage,LITV)效应。结果表明:在800和870℃分别保温24 h条件下可获得纯相层片状Ca3Co4O9多晶,其(00l)取向因子达0.74。Ca3Co4O9多晶材料在80~300 K、336~826 K分别为金属和半导体电输运行为。336 K时Seebeck系数约130μV/K。由于声子曳引热电势的贡献,随温度升高,热电势增大。以波长为248 nm、脉宽为28 ns、能量密度为17 m J/cm2的脉冲激光照射多晶构造斜面,获得了42 m V的LITV响应,比倾斜外延Ca3Co4O9薄膜中的LITV信号小约2个数量级。由于存在偏离(00l)取向的晶粒和大量晶界,导致本征热电各向异性相互抵消,大大减小了LITV响应。

Misfit-layered Ca3Co4O9 polycrystalline bulks with c-axis orientation were prepared via solid-state reaction. The Ca3Co4O9 bulks were characterized by thermogravimetric-differential scanning calorimetry, X-ray diffraction and scanning electron microscopy, respectively. The thermoelectric properties and the laser induced transverse voltage (LITV) effect of Ca3Co4O9 bulk were investigated. The results show that the layered Ca3Co4O9 bulks with a pure phase and (00l) lotgering factor of 0.74 can be obtained after sintered at 800 and 870 ℃ for 24 h, respectively. The polycrystalline bulks exhibit metallic and insulator electrical transport behaviors at 80-300 K and 336-826 K, respectively. The Seebeck coefficient is 130 μV/K at 336 K and increases with the increasing temperature which due to the contribution of phonon drag thermopower. Under the irradiation of pulsed laser (i.e., λ=248 nm, pulse width=28 ns, energy density=17 mJ/cm2), the LITV response is obtained along the inclined direction with a peak voltage of 42 mV, which is nearly two orders of magnitude lower than that in tilted epitaxial Ca3Co4O9 film. This is mainly due to the intrinsic Seebeck tensor anisotropy of the material, which is neutralized by the grains with orientations deviated from (00l) and lots of grain boundaries, thus reducing the LITV response.
©, 2015, Chinese Ceramic Society. All right reserved.