Structures and Magnetic Ordering in Layered Cr Oxide Arsenides Sr(2)CrO(2)Cr(2)OAs(2) and Sr(2)CrO(3)CrAs

[Image: see text] Two novel chromium oxide arsenide materials have been synthesized, Sr(2)CrO(2)Cr(2)OAs(2) (i.e., Sr(2)Cr(3)As(2)O(3)) and Sr(2)CrO(3)CrAs (i.e., Sr(2)Cr(2)AsO(3)), both of which contain chromium ions in two distinct layers. Sr(2)CrO(2)Cr(2)OAs(2) was targeted following electron microscopy measurements on a related phase. It crystallizes in the space group P4/mmm and accommodates distorted CrO(4)As(2) octahedra containing Cr(2+) and distorted CrO(2)As(4) octahedra containing Cr(3+). In contrast, Sr(2)CrO(3)CrAs incorporates Cr(3+) in CrO(5) square-pyramidal coordination in [Sr(2)CrO(3)](+) layers and Cr(2+) ions in CrAs(4) tetrahedra in [CrAs](−) layers and crystallizes in the space group P4/nmm. Powder neutron diffraction data reveal antiferromagnetic ordering in both compounds. In Sr(2)CrO(3)CrAs the Cr(2+) moments in the [CrAs](−) layers exhibit long-range ordering, while the Cr(3+) moments in the [Sr(2)CrO(3)](+) layers only exhibit short-range ordering. However, in Sr(2)CrO(2)Cr(2)OAs(2), both the Cr(2+) moments in the CrO(4)As(2) environments and the Cr(3+) moments in the CrO(2)As(4) polyhedra are long-range-ordered below 530(10) K. Above this temperature, only the Cr(3+) moments are ordered with a Néel temperature slightly in excess of 600 K. A subtle structural change is evident in Sr(2)CrO(2)Cr(2)OAs(2) below the magnetic ordering transitions.