Sr2CoWO6 perovskite has been prepared in polycrystalline form by solid-state reaction at 1150 °C. This material has been studied by high-resolution synchrotron X-ray and neutron powder diffraction (NPD), magnetic measurements, and differential scanning calorimetry (DSC). At room temperature, the crystal structure is tetragonal, space group I4/m, with a = 5.58277(1) Å and c = 7.97740(1) Å. The structure contains alternating CoO6 and WO6 octahedra, tilted in anti-phase by 7.24° in the basal ab plane along the [001] direction of the pseudocubic cell. This corresponds to the a 0 a 0 c - Glazer's notation as derived by Woodward for 1:1 ordering of double perovskites, consistent with space group I4/m. DSC and NPD measurements as a function of temperature indicate a structural transition from tetragonal to monoclinic (space group P21/n) at 260 K. At 2 K the cell parameters are a = 5.61267(8) Å, b = 5.58753(8) Å, c = 7.8994(1) Å, and β = 90.041(3)°. The structure contains alternating CoO6 and WO6 octahedra, tilted in-phase by 4.77° along the [001] direction of the pseudocubic cell and in anti-phase by 5.82° along the [010] and [100] directions. This corresponds to the a - a - c + Glazer's notation as derived by Woodward for 1:1 ordering in double perovskites, consistent with space group P21/n. Magnetic and neutron diffraction measurements indicate an antiferromagnetic ordering below T N = 24 K. The magnetic moment calculated through the linear fit of the Curie−Weiss law at high temperatures (5.20 μB) indicates that the orbital contribution is unquenched at high temperatures, which is consistent with high-spin Co2+ (4T1g ground state) in a quasi-regular octahedral environment. As prepared, the sample is an electrical insulator. Magnetic and electrical properties and bond valence sums are consistent with the electronic configuration Co2+(3d7)−W6+(5d0).

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, magnetotransport, and Hall effect measurements. At room temperature, the crystal structure is tetragonal with a space group I4/m, with a = 5.565 03(5) and c = 7.948 10(8) Å. The crystal contains alternating CoO6 and MoO6 octahedra, tilted by 6.8° 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 H2/N2 flows, leads to oxygen-deficient double perovskites, Sr2CoMoO6 - δ, δ = 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 H2 reduction; the number of charge carriers, as determined by Hall effect measurements, are 1.7 × 10-7 and 6 × 10-6 electrons per unit cell for δ = 0.03 and 0.14 samples, respectively. Moreover, the reduced samples exhibit colossal magnetoresistance, 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 t2g electrons, injected through hydrogen reduction.