Journal
CHEMISTRY OF MATERIALS
Volume 14, Issue 2, Pages 812-818Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cm011186j
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Sr2CoMoO6 perovskite has been prepared in polycrystalline form by thermal treatment, in air, of previously decomposed citrate precursors. This material has been studied by X-ray (XRD) and neutron powder diffraction (NPD), thermal analysis, and magnetic, magneto-transport, and Hall effect measurements. At room temperature, the crystal structure is tetragonal with a space group l4/m, with a = 5.565 03(5) and c = 7.948 10(8) Angstrom. The crystal contains alternating CoO6 and MoO6 octahedra, tilted by degrees6.8 in the basal ab plane. Magnetic measurements indicate an antiferromagnetic ordering below T-N = 37 K. As prepared, the sample is an electrical insulator. The topotactic reduction of the stoichiometric sample, in H-2/N-2 flows, leads to oxygen-deficient double perovskites, Sr2COMoO6-delta, delta = 0.03 and 0.14. The magnetic behavior of the reduced samples suggests the presence of ferromagnetic domains characterized by Curie temperatures of T-C = 350-370 K. The conductivity dramatically increases upon H-2 reduction; the number of charge carriers, as determined by Hall effect measurements, are 1.7 x 10(-7) and 6 x 10(-6) electrons per unit cell for delta = 0.03 and 0.14 samples, respectively. Moreover, the reduced samples exhibit colossal magneto-resistance, as high as 30% at 12 K for H = 9T. Magnetic and magnetotransport results are consistent with a large component of itinerancy for down-spin Mo t(2g) electrons, injected through hydrogen reduction.
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