ABSTRACT
The difference is important and is due to the different arrangement of oxygen atoms, which determines the oxidation state of the cations. These important details were only discovered with neutron diffraction, since the x-ray scattering power of the heavy bismuth and thallium atoms masks the weak scattering from oxygen. Hervieu et al. report that some of the substituted compounds contain quite complicated superstructures that remain to be explained. The thallium oxide layers are not naturally commensurable with the copper oxide layers, and this results in superstructures which while not in themselves important for superconductivity, mean that dopants can be more easily accommodated. The relative volatility of thallium oxide also means that the materials are sensitive to the oxidation–reduction conditions of preparation.
