  The complex metal oxides Ni2InSbO6 (NISO) and Ni2ScSbO6 (NSSO) have been
prepared in form of polycrystalline powders by a solid state reaction route.
The crystal structure and magnetic properties of the compounds were
investigated using a combination of X-ray and neutron powder diffraction,
electron microscopy, calorimetric and magnetic measurements. The compounds
adopt a trigonal structure, space group R3, of the corundum related Ni3TeO6
(NTO) type. Only one of the octahedral Ni positions (Ni(2)) of the NTO
structure was found to be occupied by In (Sc). NTO has non-centrosymmetric
structure and is ferroelectric below 1000 K, dielectric and second harmonic
measurements suggest that also NISO and NSSO are correspondingly ferroelectric.
Magnetization measurements signified antiferromagnetic ordering below TN=60 K
(NSSO) and 76 K (NISO). The magnetic structure is formed by two
antiferromagnetically coupled incommensurate helices with the spiral axis along
the b-axis and propagation vector k = [0, ky,0] with ky= 0.036(1) (NSSO) and
ky= 0.029(1) (NISO). The observed structural and magnetic properties of NISO
and NSSO are discussed and compared with those of NTO.
