Marin Cernea

Preparation and characterization of Ce-doped BaTiO3 thin films by r.f. sputtering

Ce-doped BaTiO3 thin films prepared on silicon-platinium by r.f. sputtering has been investigated. BaTiO3 doped with 5.5 mol%CeO2 thin film was deposited at 550°C substrate temperature in an Ar atmosfere. The crystal structure and shape were examined by X-ray diffraction and scanning electron microscopy with EDAX. Analysis by X-ray diffraction patterns show that the crystalline film with a cubic structure of BaTiO3, was obtained. The surface morphology (roughness, the grain size and the droplet size) of the thin film surface was examined by atomic force microscopy (AFM). The grain size is about 160 nm, the droplet size is about 0.675 μm and the roughness is 36.88 nm. EDAX analysis established a composition of the film to be identical with that of the target (BaTiO3 doped with 5.5 mol%CeO2). The broad peak in the capacitance versus temperature curve at the Curie point indicate that the r.f. sputtered Ce-doped BaTiO3 film is ferroelectric. The values of the capacitance of the thin film at 1 KHz were found to be 86 pF and the loss dielectric was tan δ = 0.0875. The film exibits a dielectric anomaly peak at 23°C showing ferroelectric to paraelectric phase transition.

Electrical investigations of holmium-doped BaTiO 3 derived from sol-gel combustion

Holmium-doped BaTiO 3 with composition Ba 0.97 Ho 0.03 TiO 3 was prepared by sol-gel combustion method. A molar ratio of citrate/nitrate (CA / NO 3 − = 1.3) was used to prepare nanopowders of (Ba,Ho)TiO 3 . The structure and microstructure of (Ba,Ho)TiO 3 powders and ceramics were investigated. The ceramics exhibit a dielectric constant of about 4400 and dielectric loss (tan δ = 0.267) at 10 Hz, and at the Curie temperature ( T c = 132 °C). The remanent polarization and the coercive field of Ba 0.97 Ho 0.03 TiO 3 ceramics, at 1 kHz, were P r = 6 μC/cm 2 and E C = 0.75 kV/cm. The dielectric and ferroelectric behavior of the holmium-doped BaTiO 3 is influenced by the amphoteric character of Ho 3+ ions.

Development and Biocompatibility Evaluation of Photocatalytic TiO2/Reduced Graphene Oxide-Based Nanoparticles Designed for Self-Cleaning Purposes

Graphene is widely used in nanotechnologies to amplify the photocatalytic activity of TiO2, but the development of TiO2/graphene composites imposes the assessment of their risk to human and environmental health. Therefore, reduced graphene oxide was decorated with two types of TiO2 particles co-doped with 1% iron and nitrogen, one of them being obtained by a simultaneous precipitation of Ti3+ and Fe3+ ions to achieve their uniform distribution, and the other one after a sequential precipitation of these two cations for a higher concentration of iron on the surface. Physico-chemical characterization, photocatalytic efficiency evaluation, antimicrobial analysis and biocompatibility assessment were performed for these TiO2-based composites. The best photocatalytic efficiency was found for the sample with iron atoms localized at the sample surface. A very good anti-inhibitory activity was obtained for both samples against biofilms of Gram-positive and Gram-negative strains. Exposure of human skin and lung fibroblasts to photocatalysts did not significantly affect cell viability, but analysis of oxidative stress showed increased levels of carbonyl groups and advanced oxidation protein products for both cell lines after 48 h of incubation. Our findings are of major importance by providing useful knowledge for future photocatalytic self-cleaning and biomedical applications of graphene-based materials.