Synthesis of Spinel-Type Magnesium Cobalt Oxide and Its Electrical Conductivity
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This work devotes to investigate synthesis and electrical properties of spinel MgCo<SUB>2</SUB>O<SUB>4</SUB> that is considered as a candidate of the cathode materials of magnesium-ion batteries in future. Samples were synthesized by two types of techniques: solid-state reaction and wet process. The crystal structures of the samples were analyzed by X-ray diffraction, and their electrical conductivities were obtained through the dc resistance and ac impedance measurements. By solid-state reaction, sample of a single MgCo<SUB>2</SUB>O<SUB>4</SUB> phase was not obtained; a sample synthesized at 800°C for 24 h after milling of Co<SUB>3</SUB>O<SUB>4</SUB> and MgO powder was comprised of dual phases of spinel-type and rocksalt-type structures, and samples synthesized at temperatures higher than 880°C showed a single rocksalt-type phase without electrical conductance. The former sample showed p-type semiconducting behavior as well as spinel-type Co<SUB>3</SUB>O<SUB>4</SUB>, but its electrical conductivity around room temperature was shown to exceed that of Co<SUB>3</SUB>O<SUB>4</SUB>. In contrast, a sample consisting of a single spinel-type phase was successfully synthesized by wet process, which exhibited an electrical conductivity of the order 10<SUP>−2</SUP> Scm<SUP>−1</SUP>, being much higher than those of the samples synthesized by solid-state reaction. Thus, substitution of Co<SUP>2+</SUP> in Co<SUB>3</SUB>O<SUB>4</SUB> with Mg<SUP>2+</SUP> is found to enhance the electrical conductivity of the spinel-type phase.
- Materials Transactions, JIM
Materials Transactions, JIM 49(4), 824-828, 2008-04-01
The Japan Institute of Metals and Materials