A combinatorial nanoprecursor route for direct solid state chemistry: Discovery and electronic properties of new iron-doped lanthanum nickelates up to La4Ni2FeO10 − δ

We describe a simple nanoprecursor route for direct solid-state combinatorial synthesis and discovery of heterometallic materials compositions which are normally difficult to make in a single step. Using a combinatorial robot (incorporating a continuous hydrothermal reactor), co-precipitated nanoprecursors containing different amounts of La, Ni and Fe oxides were made. These samples were divided into two identical cloned libraries, which were heat-treated to bring about solid-state transformations at either 1348 K or 1573 K for 12 h. In each case, experimental conditions were designed to form the corresponding La4Ni3 − xFexO10 phases (x = 0.0–3.0) directly without comminution. Such materials are difficult to make without multiple heating and grinding steps. The heat-treated samples from each library were embedded into a wellplate and analysed by powder X-ray diffraction methods in order to elucidate trends in phase behaviour. Several hitherto unknown phase-pure Ruddlesden Popper type La4Ni3 − xFexO10 compositions were identified and their DC electrical conductivities measured.