Resumen de Sustainable materials by electrodeposition and sputter deposition methods
This thesis dissertation includes the synthesis and characterization of sustainable materials including bismuth (Bi), bismuth ferrite (BiFeO3) and copper-based shape memory alloys. Electrodeposition and sputter deposition were employed as the synthesis techniques. Electrodeposition was used in order to obtain micron and submicron sized Bi particles from an aqueous electrolyte and BiFeO3 films when electrodeposition from dimethylformamide bath was followed by heat treatment of the resulting coatings in open air. Sputter deposition was applied to produce copper-aluminium-nickel (Cu–Al–Ni) shape memory alloys. Two approaches were followed to obtain the Cu–Al–Ni thin films. In one of the methods applied, multilayers of Cu-Ni and Al were first sputtered, followed by heat treatment and quenching in iced water while, in the other method, epitaxial growth of austenitic Cu–Al–Ni on MgO substrate was obtained by sputter deposition along with in-situ heat treatment. Morphological characterization of the samples was carried out by scanning electron microscopy (SEM). X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for structural characterization. For the investigation of magnetic properties of the bismuth ferrite films, vibrating sample magnetometry (VSM) was implemented. In order to observe the martensitic transformation behaviour in the sputter deposited Cu–Al–Ni films, electrical resistivity measurements with respect to temperature were carried out. The morphology of the Bi particles was investigated as a function of the bath composition, substrate activity and the applied potential. In all cases, it was seen that as the absolute value of the applied potential increased, an evolution in the particle morphology from hexagons to dendrites was observed. Moreover, Bi particles were more uniformly distributed over the substrate when sodium gluconate was added to the electrolyte. The characterization studies for the BiFeO3 films prepared by electrodeposition and subsequent heat treatment revealed that rhombohedral BiFeO3 (interesting for its multiferroic character) formed around 600 °C. At lower and higher temperatures, secondary binary and ternary oxide phases were encountered. The observed weak ferromagnetic-like behaviour in the film annealed at 600 °C is mainly ascribed to nanostructuration which, in turn, favours the occurrence of spin canting in the BiFeO3 phase. In the free-standing Cu–Al–Ni films prepared by sputter deposition and subsequent heat treatment, it was observed that a gradual change in the film composition (i.e. decrease in the Al content and an increase in the Ni content) resulted in a shift in the room temperature phase formation from martensite to austenite. The obtained films exhibited a randomly oriented polycrystalline structure. On the other hand, for the austenitic Cu–Al–Ni film grown at high temperature on MgO substrates, a (200) textured growth of the film was observed due to the epitaxial relationship between the film and the substrate. The electrical resistance change vs. temperature measurements revealed that martensitic transformation was observed in the textured austenite film whereas it was not observed in the randomly oriented austenite film. The potential of the materials investigated throughout this Thesis as sustainable candidates in micro- and nanosystems is outlined.
