Synthesis, Crystal Structure, and Structural Features of Solid Solutions Ba(Cr1–xCox)2As2 - New Layered Arsenides with the ThCr2Si2 Structure

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A series of Ba(Cr1–xCox)2As2 solid solutions is obtained for the entire range of compositions as polycrystalline samples (x = 0, 0.2, 0.3, 0.4, 0.6, 0.7, 0.8, 1.0) and single crystals (x = 0.8). By single crystal X-ray diffraction it is found that mixed arsenides Ba(Cr1–xCox)2As2 belong to the ThCr2Si2 structure type. They consist of antifluorite-like [TAs]– layers separated by Ba2+ cations. The layers are formed by [TAs4] tetrahedra with common edges, T = Cr, Co atoms statistically occupy sites of the square planar network at T⋯T distances of 2.80-2.82 Å, which assumes the possible magnetic interaction. As cobalt substitutes for chromium, the T–As bond length gradually decreases, which decreases the [TAs]– layer thickness, with the distance between As atoms from the neighboring layers remaining almost unchanged. The crystal chemical characteristics of Ba(Cr1–xCox)2As2 solid solutions are in general well consistent with those of isoelectronic representatives of the 122 family, except BaMn2As2 having a number of significant distinctions in the structure, which is due to a large radius of the Mn2+ cation (d5, hs). Based on the obtained structural data, the magnetic behavior of Ba(Cr1–xCox)2As2 solid solutions is theoretically evaluated.