SYNTHESIS AND CHARACTERIZATION OF A NEW COMPOUND WITH ALTERNATING MNO22- AND ZN2AS22- LAYERS - BA2MNZN2AS2O2

A new mixed transition metal pnictide oxide, Ba2MnZn2As2O2, is reporte d. Ba2MnZn2As2O2 has been prepared in quantitative yield from heating stoichiometric amounts of BaO with the elements, which are pressed int o a pellet, placed in an Al2O3 boat, and sealed in a fused silica ampu le, at 1000 degrees C. This compound is an ordered variant of the Sr2M n3As2O2 structure type and crystallizes in the tetragonal space group I4/mmm (Z = 2). Single-crystal X-ray data (130 K) were refined (a = 4. 2317(3) Angstrom, c = 19.443(2) Angstrom R1 = 2.96%, wR2 = 6.84%). The structure is made up from square planar MnO2 layers with layers of Zn 2As2 tetrahedra interspersed by alkaline earth cations such that the f ormula may be written as Ba-2(MnO2)(Zn2As2). Rietveld refinement (a = 4.24257(8) Angstrom, c = 19.5087(7) Angstrom, R-wp = 9.26%, R-p = 6.44 %) of powder neutron diffraction data obtained at room temperature pro vides unambiguous evidence for this ordered model in the case of Ba2Mn Zn2As2O2. Magnetic studies in the temperature range 5 less than or equ al to T/K less than or equal to 300 show antiferromagnetic ordering at 38 K with spin glasslike behavior at low temperatures.