Effect of High Cobalt Concentration on Hopping Motion in Cobalt Manganese Spinel Oxide (CoxMn3–xO4, x ≥ 2.3)

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• 作者：HyukSu Han ; Jae Seok Lee ; Jeong Ho Ryu ; Kang Min Kim ; Jacob L. Jones ; Jiun Lim ; Sophie Guillemet-Fritsch ; Han Chan Lee ; Sungwook Mhin
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：June 30, 2016
• 年：2016
• 卷：120
• 期：25
• 页码：13667-13674
• 全文大小：499K
• 年卷期：0
• ISSN：1932-7455

文摘

Hopping motions in cobalt manganese spinel oxides with high cobalt concentration (Co_xMn_3–xO₄, 2.3 ≤ x ≤ 2.7) are investigated in order to clarify the origin of unusual electrical behaviors as negative temperature coefficient (NTC) thermistors. Based on the resistance versus temperature (R–T) characteristics, hopping conduction mechanisms in MCO compounds (x = 2.3 and 2.5) are attributed to variable range hopping (VRH) motion with a parabolic distribution of the density of states (DOS) near the Fermi level. However, when Co content increases up to 2.7, transition in the hopping motion occurs from VRH to the nearest neighboring hopping (NNH) motion, which can be responsible for a huge increase of the resistance accompanied by decrease of the factor of thermal sensitivity (B value) in MCO compounds (x = 2.7). Also, hopping distance and activation energies for MCO (x = 2.3 and 2.5) compounds following VRH conduction are calculated as a function of temperature, indicating that higher B value observed in MCO (x = 2.5) compound is due to the larger hopping distance compared to that of MCO (x = 2.3) compound.