Synthesis and Characterisation of Complex Oxychalcogenides

Mixed-anion compounds like oxychalcogenides, where there are both oxide anions and chalcogen anions (S-Te) create quite a rare class of materials which is gaining increasing attention. The anions have different sizes and chemical requirements which promise ordering of the oxide crystallographically, whereby their structures can be described as a mixture of 2-D structural building blocks (e.g. perovskite, fluorite, or rock-salt) stacked on top of each other along a given

which are absent in Mn2O or Co2O systems, implying that they are exclusively to the Fe2O layers and could be sensitive to the distance between Fe2O layers. Isovalent doping LaGaOS2 with Nd and Ce ions onto the La site gave limited solid solutions. From the diffuse reflectance spectroscopy data, Nd-doping and Ce-doping the parent compound gave no significant change in optical band gaps and

the colour change observed in colour in Nd-doped samples are presumably due to f-f transitions. This work suggests that LaGaOS2 has a quite limited compositional flexibility in its structure and that it is not easy to modify its electronic structure using chemical pressure. Electron doping BiCuOSe with Ce (onto the Bi3+ site) and F ions (onto the O2- site) gave limited solid solutions. BiCuOSe had some Cu vacancies. The Ce-doped samples contained Ce4+ ions. Electron doping BiCuOSe with F gave metallic compounds, while doping BiCuOSe with Ce gave compounds with both semiconducting and metallic behaviour. The semiconducting behaviour may be due to impurities.