Metal-insulator transition in RNiO₃ nanotubes

Full text: Strongly correlated RNiO₃ compounds have been extensively studied due to their sharp metal-insulator transition, which critical temperature T_MI can be tuned with the rare earth size. This work describes physical characterization of RNiO₃ (R= Pr, Nd, Sm) nanostructures, which were prepared using the pore-filling wetting technique. In this procedure, stoichiometric polymeric precursor solutions with RNi- O were prepared and commercial mesoporous anodic aluminum oxide templates were immersed in these polymeric resins. The samples were dried and heat treated at 700°C in low oxygen pressure. After the heat treatment, the template were dissolved by using a 4 M KOH solution, the nanostructured oxide were then separated, and washed with water using several successive centrifuging-washing steps. Samples were characterized by X-ray diffraction, scanning electron microscopy (SEM) and magnetization measurements M(T) as a function of temperature. X-ray diffraction patterns of the RNiO₃ nanotubes revealed that all samples are polycrystalline and crystallize in an orthorhombically distorted perovskite structure (Pbnm space group symmetry). The SEM images of these samples show samples with ultrafine grains assembled in nanotubes. Analysis of these images revealed samples with external diameters ranging from 200 to 300 nm and with lengths close to 5 μm. The electrical transport properties and M(T) measurements will be performed to verify a metal insulator transition and an antiferromagnetic ordering in these samples, both electrical and magnetic transitions should occur around 145 K, 200 K and ~400 K for the PrNiO₃, NdNiO₃ and SmNiO₃, respectively. Finally, it will be evaluate the possibility to apply these RNiO₃ 1D oxides to build pressure and memory devices through a field effect transistor set up. (author)