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首页> 外文期刊>Journal of Physics, D. Applied Physics: A Europhysics Journal >High temperature thermoelectric power study on calcium substituted lanthanum manganites
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High temperature thermoelectric power study on calcium substituted lanthanum manganites

机译：钙取代镧锰的高温热电研究

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摘要

Compositional and temperature dependent thermoelectric power measurements have been performed on the polycrystalline manganite perovskite system: La1- x Ca (x) MnO3+ (delta) ( x = 0.00, 0.25, 0.33, 0.50 and 1.00), in the paramagnetic state ( T > Tc) ( 300 - 673 K). The Seebeck coefficient ( a) has been used to calculate the Fermi energy, the activation energy ( Ea), the Mn4+- ion concentration and the oxygen content ( d), for different compositions. The observed decrease in Ea with increase in Ca- concentration and a large value of Ea as compared with a relatively high temperature sintered material of the same compositions have been explained in the light of the decrease in the interatomic distances and grain growth with Ca- substitution. It is shown that [ Mn4+][ Mn3+] ion concentration is not the only factor that governs conduction in the manganite perovskites. The significantly small values of a (- 22 mu VK- 1) at high temperature can be explained on the basis of ( Mn3+ - Mn3+) charge disproportionation into stable Mn2+ - Mn4+ pairs in the system rather than on the basis of nominal Mn3+/ (4+) valence arguments. Finally, nearly temperature independent variation of a, charge- carrier concentration at high temperature and low value of mobility are hallmarks of small polaron hopping.
机译：在多晶锰钙钛矿钙钛矿体系上进行了成分和温度相关的热电功率测量：La1- x Ca（x）MnO3 +（δ）（x = 0.00、0.25、0.33、0.50和1.00），处于顺磁状态（T> Tc ）（300-673 K）。 Seebeck系数（a）已用于计算不同组成的费米能，活化能（Ea），Mn4 +-离子浓度和氧含量（d）。与相同组成的相对较高温度的烧结材料相比，观察到的Ea随Ca浓度的增加而降低，并且Ea值较大，这是由于原子间距离的减小和Ca取代引起的晶粒长大所致。 。结果表明，[Mn4 +] [Mn3 +]离子浓度不是控制锰钙钛矿中导电性的唯一因素。高温下（-22μVK-1）的极小值可以基于系统中稳定的Mn2 +-Mn4 +对中的（Mn3 +-Mn3 +）电荷歧化而不是基于标称Mn3 + /（ 4+价键参数。最后，高温下载流子浓度的几乎与温度无关的变化和迁移率的低值是小极化子跳跃的标志。

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