Production of LaCaMnO nanowires and nanoparticles by sol-gel method and their properties

The perovskite manganites are well-known compounds for their colossal magnetoresistive (CMR) properties. So far perovskite manganites have been fabricated as a bulk, thin or thick film form by employing many different techniques such as conventional solid state reaction, electroless plating, chemical vapor deposition and sol-gel. Nanoparticles and nanowires of perovskite manganites have recently been shown to exhibit strikingly different phases and properties compared to those of their bulk counterparts. These quasi one dimensional materials have attracted much attention due to their significant technological applications in optical, electrical and magnetic devices.In this thesis, densely packed LaCaMnO nanowires were synthesized within a porous anodic aluminum oxide (AAO) template by means of sol-gel method using nitrate as raw the material and ethylene glycol as the chelating agent. Firstly, The AAO templates were prepared by the conventional two-step anodic oxidation procedure Different times of anodic oxidation and wet etching were investigated to find conditions suitable for the production of ordered high-density nanopores of various diameters.Secondly, a system has been designed for nanowire production. The sol-gel synthesis and template preparation of nanomaterials for densely packed LaCaMnO nanowires has been combined. The gel formed at 192 °C was slowly filled to nanoporous using vacuum pump. Then it has been annealed in air atmosphere at 400 °C for 2 hours and then 700 °C for 2 hours. Also residual part of the gel from the filtered nanoporous was annealed in air atmosphere at 700 °C, 1073 °C and 1400 °C.The scanning electron microscopy (SEM), field emission electron microscopy (FESEM) and atomic force microscopy (AFM) images showed that nanowires are almost parallel and their diameter is around 200 nm. Energy dispersive X-ray analysis(EDX) was done to confirm the structure of nanowires and nanoparticles of desired composition. It was observed from the reduced hysteressis curves, that the magnetic behavior of the LaCaMnO nanowire arrays was strongly dependent pH of solution. On the contrary of nanoparticles, it was found that nanowires produced at pH3 show ferromagnetic properties at room temperature.KEYWORDS: nanopores, AAO, nanoparticles, nanowires, sol-gel, perovskite manganites, ferromagnetic,