Rock-salt NiO and Ni0.7Zn0.3O nanoparticles were investigated by x-ray diffraction, atomic-force microscopy, and magnetic measurements. Nanoparticle diameters varied from 8 to 30 nm depending on reaction conditions. There are two main magnetization contributions, the field-induced spin canting of the antiferromagnetic sublattices and the magnetization rotation caused by uncompensated spins interacting with the magnetic field. The former is a bulk effect, modified by the presence of Zn, whereas the latter is a nanoscale effect that increases with decreasing particle size. The relative contributions of the two effects depend on particle size with a critical size of about 18 nm resulting in bulklike behavior.

Metal nitrides have potential in energy applications because of their physical and optical properties. Nanoparticle composites of titanium nitride (TiN) and titanium dioxide (TiO2) were investigated for their photocatalytic hydrogen (H2) evolution activity via methanol reformation. Physical mixing of the nanoparticulate TiO2 and TiN was employed to prevent the oxy-nitride formation and particle aggregation observed in thermal preparations. This convenient combination of TiO2 and TiN demonstrated a substantial synergistic effect with enhanced activity (9.4 μmol/h TiO2–TiN vs 1.8 μmol/h TiO2) under combined UV/vis light. Irradiation under only UV light resulted in a similar enhancement factor compared to using combined UV/vis light, demonstrating that the enhanced activity of the composites occurs essentially for UV-driven photocatalysis. No activity/enhancement was observed with only visible light irradiation; however, minor enhancement was observed when switching between UV and UV/vis irradiation, suggesting a contribution from the TiN plasmon. We propose that the plasmonic contribution is dependent on the band gap excitation of TiO2, which reduces the degree of band bending at the TiO2/TiN interface. This promotes the migration of hot electrons from TiN away from the TiO2/TiN interface to be used for H2 evolution.

Fe4Si2Sn7O16 has a unique crystal structure that contains alternating layers of Fe(2+) ions octahedrally coordinated by O (oxide layer) and Sn (stannide layer), bridged by SiO4 tetrahedra. The formula can be written as FeFe3Si2Sn7O16 to emphasise the distinction between the layers. Here, we report the changes in structure and properties as iron is selectively replaced by manganese in the oxide layer. Solid-state synthesis was used to produce polycrystalline samples of Fe(Fe3-xMnx)Si2Sn7O16 for x≤ 2.55, the structures of which were characterised using high-resolution synchrotron X-ray and neutron powder diffraction. Single-crystal samples were also grown at x = 0.35, 0.95, 2.60 and characterised by single crystal X-ray diffraction. We show that manganese is doped exclusively into the oxide layer, and that this layer contains exclusively magnetically active high-spin M(2+) transition metal cations; while the stannide layer only accommodates non-magnetic low-spin Fe(2+). All samples show clear evidence of geometrically frustrated magnetism, which we associate with the fact that the topology of the high-spin M(2+) ions in the oxide layer describes a perfect kagomé lattice. Despite this frustration, the x = 0 and x = 2.55 samples undergo long-range antiferromagnetic ordering transitions at 3.0 K and 2.5 K, respectively.