p-Type thermoelectric properties of the oxygen-deficient perovskite Ca₂Fe₂O₅ in the brownmillerite structure

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• 作者：Emily Asenath-Smith ; Indunil N. Lokuhewa ; Scott T. Misture ; Doreen D. Edwards
• 关键词：Calcium ferrite ; Brownmillerite ; Thermopower ; Seebeck coefficient ; Thermal properties ; Electrical conductivity ; Disproportionation
• 刊名：Journal of Solid State Chemistry
• 出版年：2010
• 出版时间：July 2010
• 年：2010
• 卷：183
• 期：7
• 页码：1670-1677
• 全文大小：792 K

文摘

Brownmillerite calcium ferrite was synthesized in air at 1573 K and thermoelectric properties (direct current electrical conductivity σ, Seebeck coefficient α, thermal conductivity κ, thermal expansion α_L) were measured from 373 to 1050 K in air. Seebeck coefficient was positive over all temperatures indicating conduction by holes, and electrical properties were continuous through the Pnma–Imma phase transition. Based on the thermopower and conductivity activation energies as well as estimated mobility, polaron hopping conduction was found to dominate charge transport. The low electrical conductivity, <1 S/cm, limits the power factor (α²σ), and thus the figure of merit for thermoelectric applications. The thermal conductivity values of 2 W/mK and their similarity to Ruddlesden–Popper phase implies the potential of the alternating tetrahedral and octahedral layers to limit phonon propagation through brownmillerite structures. Bulk linear coefficient of thermal expansion (14×10⁻⁶ K⁻¹) was calculated from volume data based on high-temperature in situ X-ray powder diffraction, and shows the greatest expansion perpendicular to the alternating layers.