Structure and magnetic properties of the α-NaFeO2-type honeycomb compound Na3Ni2BiO6.

We present the structure and magnetic properties of Na3Ni2BiO6, which is an ordered variant of the α-NaFeO2 structure type. This layered compound has a 2:1 ordering of (Ni(2+)/Bi(5+))O6 octahedra within the a-b plane and sodium in octahedra between the layers. The structure is presented in the space group C2/m, determined through a combination of single crystal X-ray, powder neutron, and powder X-ray diffraction. Temperature dependent magnetic susceptibility measurements show Na3Ni2BiO6 to display long-range antiferromagnetic ordering below 11 K, despite the dominance of ferromagnetic interactions above TN as indicated by a positive Weiss constant. Heat capacity measurements and low-temperature neutron diffraction support the magnetic ordering and are consistent with a TN of 10.4 K. A magnetic phase can be refined with (010) antiferromagnetic ordering along the b-axis in the honeycomb layer and moments aligned parallel to c. The compounds Na3Mg2BiO6 and Na3Zn2BiO6, synthesized as nonmagnetic analogues of Na3Ni2BiO6, are briefly described.