Synthesis and Characterization of a New Compound with Alternating MnO 2 2 - and Zn 2 As 2 2 - Layers: Ba 2 MnZn 2 As 2 O 2

A new mixed transition metal pnictide oxide, Ba 2 MnZn 2 As 2 O 2, is reported. Ba 2 MnZn 2 As 2 O 2 has been prepared in quantitative yield from heating stoichiometric amounts of BaO with the elements, which are pressed into a pellet, placed in an Al 2 O 3 boat, and sealed in a fused silica ampule, at 1000 °C. This compound is an ordered variant of the Sr 2 Mn 3 As 2 O 2 structure type and crystallizes in the tetragonal space group I 4/ mmm ( Z = 2). Single-crystal X-ray data (130 K) were refined ( a = 4.2317(3) Å, c = 19.443(2) Å, R 1 = 2.96%, wR 2 = 6.84%). The structure is made up from square planar MnO 2 layers with layers of Zn 2 As 2 tetrahedra interspersed by alkaline earth cations such that the formula may be written as Ba 2 (MnO 2 )(Zn 2 As 2 ). Rietveld refinement ( a = 4.24257(8) Å, c = 19.5087(7) Å, R wp = 9.26%, R p = 6.44%) of powder neutron diffraction data obtained at room temperature provides unambiguous evidence for this ordered model in the case of Ba 2 MnZn 2 As 2 O 2 . Magnetic studies in the temperature range 5 ≤ T / K ≤ 300 show antiferromagnetic ordering at 38 K with spin glasslike behavior at low temperatures.