Structure and properties of the CaFe2O4-type cobalt oxide CaCo2O4

摘要: The calcium cobalt oxide CaCo{sub 2}O{sub 4} was synthesized for the first time and characterized from a powder X-ray diffraction study, measuring magnetic susceptibility, specific heat, electrical resistivity, thermoelectric power. crystallizes in CaFe{sub (calcium ferrite)-type structure, consisting of an edge- corner-shared CoO{sub 6} octahedral network. structure belongs to orthorhombic system (space group: Pnma) with lattice parameters, a=8.789(2) A, b=2.9006(7) A c=10.282(3) A. Curie-Weiss-like behavior susceptibility nearly trivalent low-spin state (Co{sup 3+}, 3dt{sub 2g}{sup 6}, S=0), semiconductor-like temperature dependence resistivity ({rho}=3x10{sup -1} {omega} cm at 380 K) dominant hopping conduction low temperature, metallic-temperature-dependent large power (Seebeck coefficient: S=+147 {mu}V/K K), Schottky-type heat small Sommerfeld constant ({gamma}=4.48(7) mJ/Co mol K{sup 2}), were observed. These results suggest that compound possesses metallic electronic density states Fermi level. doped holes are localized temperatures due disorder crystal. carriers probably originate slight off-stoichiometry phase. It also found S tends increase even more beyond K.more » is possibly attributed residual spin entropy orbital degeneracy coupled charges by strong electron correlation oxides. - Graphical abstract: new phase, which calcium-ferrite-type Pnma; A), has been under high pressure (1500 deg. C, 6 GPa). This exhibits unsaturated around K.« less