Anisotropically electrical property of Anderson insulator state in Bi2Ca2-xSrxCo2Oy (x=0.0, 0.5, 1.0, 1.5, 2.0) single crystals

Journal of Alloys and Compounds(2020)

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摘要
In this work, Bi2Ca2-xSrxCo2Oy (x = 0.0, 0.5, 1.0, 1.5, 2.0) crystals have been grown by the flux method, and their electrical properties were characterized. The analysis of temperature-dependent-resistance indicate that in-plane resistance ρab of Bi2Ca2-xSrxCo2Oy shows the Mott variable-range-hopping mechanism, while out-of-plane resistance ρc follows the thermally activated behavior, suggesting the Anderson insulator state in these crystals. The extracted localization length ξ of wave-function of all Bi2Ca2-xSrxCo2Oy samples is increased with more Sr-concentration. Quantitatively, ξ increases from 18.1 Å in Bi2Ca2Co2Oy to 29.6 Å in Bi2Sr2Co2Oy. The variable-range-hopping or thermally activated behavior is dependent on comparison between localization length ξ of samples and average distance between two neighboring defects along ab-plane or c-axis. The increased ξ from Bi2Ca2Co2Oy to Bi2Sr2Co2Oy is attributed to increased carrier concentration (equivalent to Fermi energy EF), which is also proved by X-ray photoemission spectroscopy. This work shows the delicate effect of isovalence-element replacement on the electrical conductivity of Bi2AE2Co2Oy systems, which may be instructive on how to manipulate electrical conductivity in the layered thermoelectric oxide compounds.
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关键词
Misfit cobaltites,Crystal growth,Anisotropically electrical transport,Anderson localization
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