Ternary arsenides RECo5As3 (RE = Y, Gd, Tb, Dy, Ho, Er)

• A series of new ternary arsenides RECo5As3 was synthesized from the elements.
• Structure of the TbCo5As3 and ErCo5As3 was solved from X-ray single crystal data.
• TbCo5As3 was found to have an antiferromagnetic transition at 55–60 K.

A series of new ternary arsenides RECo5As3 (RE = Y, Gd, Tb, Dy, Ho, Er) was synthesized from pure constituents. The crystal structure of TbCo5As3 and ErCo5As3 was determined by X-ray single-crystal diffraction, the structure of the other arsenides was refined from X-ray powder diffraction data. These compounds are isotypic with the YCo5P3 structure (space group Pnma, Pearson code oP36): a = 12.249(8), b = 3.803(5), c = 10.749(5) Å for GdCo5As3; a = 12.2350(10), b = 3.7896(2), c = 10.7290(7) Å, (R1 = 0.030 (wR2 = 0.038) for 828 reflections with Io > 2σ(Io)) for TbCo5As3; a = 12.225(2), b = 3.781(7), c = 10.715(5) Å for DyCo5As3; a = 12.214(4), b = 3.775(4), c = 10.709(1) Å for HoCo5As3; a = 12.2033(7), b = 3.7685(2), c = 10.7009(4) Å, (R1 = 0.039 (wR2 = 0.062) for 921 reflections with Io > 2σ(Io)) for ErCo5As3. The structure contains distorted trigonal prisms [AsRE2Co4] condensed together by edges from RE atoms to infinite zig-zag chains. TbCo5As3 was identified as having an antiferromagnetic ground state with the Néel temperature TN = 55–60 K, which is obscured by spurious metallic Co.

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