烧结温度对La_(0.9)Sr_(0.1)FeO_3热电性能的影响

Influence of sintering temperature on thermoelectric properties of La_(0.9)Sr_(0.1)FeO_3 ceramics

利用传统的固相反应分别在1250℃,1300℃,1350℃.烧结条件下制备出钙钛矿结构的La0.9Sr0.1FeO3陶瓷样品.样品的XRD粉末衍射结果显示不同烧结温度的La0.9Sr0.1FeO3陶瓷样品都是单相的正交结构,同时晶胞体积随着烧结温度的升高而减小.从样品的SEM结果看出,随着烧结温度的升高,晶粒逐渐变大,并且晶粒间的空隙逐渐减小,样品更加致密.在室温到800℃的测试温区,测试了样品的电阻率和Seebeck系数.系统的研究了不同烧结温度对样品热电性能的影响.结果表明,随着测试温度的升高,样品电阻率的变化都表现为半导体的行为,而高温下电阻率略有升高.通过拟合证明了La0.9Sr0.1FeO3陶瓷为绝热小极化子导电机理,但是在低温区和高温区的激活能不相同.在测试温区,样品的Seebeck系数为正值,表明样品的载流子为空穴.随着测试温度升高,Seebeck系数快速减小,然后达到一个饱和值.当温度高于600℃时,Seebeck系数略有增加.随着烧结温度的升高,电阻率减小,而Seebeck系数增大.因此烧结温度越高,功率因子越大,1350℃烧结的样品在727℃时得到最大的功率因子为90μW/K2m.

Perovskite La0. 9Sr0. 1FeO3 ceramics have been synthesized at 1250℃ ,1300℃ and 1350℃ by the conventional solid-state reaction technique. From their crystal structures determined by powder X-ray diffraction,we found that the lattice volume decreases with increasing sintering temperature. The scanning electronic microscope （SEM） images of surface microstructures of the samples show that the average grain size increases with increasing sintering temperature. The electrical resistivity and Seebeck coefficient have been measured between room temperature and 800℃. At low temperatures,the electrical resistivity shows a semiconductivity-like behavior. With further increasing of temperature,the electrical resistivity slightly increases. An adiabatic hopping conduction mechanism of small-polarons is suggested from the temperature dependence of the electrical resistivity,which has different activation energies at low and high temperatures. The Seebeck coefficient rapidly decreases with increasing temperature,and reaches a saturation value about 600℃. With further increasing of temperature,the Seebeck coefficient slightly increases. With the increase of sintering temperature,the electrical resistivity decreases,while the Seebeck coefficient increases. Therefore,the power factor increases with increasing sintering temperature. The highest power factor of 90 μW /K2m was obtained at 727℃ for sample sintered at 1350℃.