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The complex metal oxides Ni 2 InSbO 6 (NISO) and Ni 2 ScSbO 6 (NSSO) have been prepared in the 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 Ni 3 TeO 6 (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 noncentrosymmetric 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 T N = 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, k y ,0] with k y = 0.036(1) (NSSO) and k y = 0.029(1) (NISO). The observed structural and magnetic properties of NISO and NSSO are discussed and compared with those of NTO.

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The crystal structure and physical properties of Bi3Pb2Nb2O11Cl, a member of the Sillen−Aurivillius phase intergrowth family, have been probed using powder neutron diffraction, high-resolution transmission electron microscopy (HRTEM), second harmonic generation (SHG) tests, and alternating current impedance methods. It is shown that this compound undergoes a diffuse ferroelectric type phase transition at T c ∼ 683 K. Although the powder neutron diffraction data show that the crystal structure has pseudo-tetragonal symmetry (parent space group P4/mmm, a p = 3.910 38(6) and c p = 18.8342(3) Å at 298 K), electron diffraction data clearly show a weak superlattice (a o ∼ b o ∼ (2)1/2 a p, c o = c p) compatible with a reduction of symmetry to orthorhombic, analogous to that observed in the related Aurivillius phases, such as SrBi2Ta2O9. Detailed analysis of the SHG data as a function of temperature suggests the existence of ordered polar nanodomains, compatible with the observation of “average” tetragonal symmetry in the neutron diffraction data. These observations, together with the presence of marked frequency dependence of T c, point toward a relaxor type ferroelectric behavior. The nature of the crystal structure, namely, a regular intergrowth of Aurivillius-like and Sillen-like blocks, [M2O2]/[MNb2O7]/[M2O2]/[Cl] [M = Bi, Pb], has been established from both Rietveld refinement of the powder neutron data and directly from HRTEM images. The observation of ferroelectricity in this material suggests the existence of a wider family of new ferroelectrics analogous to the Aurivillius phases.