engleski

Study of barium titanate on transparent titania nanotubes arrays

BaTiO3 (BTO) has been a extensively investigated material over the past 60 years due to its attractive properties, such as mechanical and chemical stability and ferroelectricity at room temperature. Due its high dielectric constant and low-loss, BTO has been used in a wide range of applications, including multilayer ceramic capacitors, gate dielectrics, piezoelectric devices, waveguide modulators, IR detectors, and for holographic memories. The dielectric properties of BTO are controlled by purity and microstructure which are dependent on the methods of preparation Moreover, it was shown recently that BTO nanostructures have humidity sensing properties [1, 2]. In this work BaTiO3 on TiO2 nanotubes arrays (BTO@TNT) were synthesized by hydrothermal processing of transparent titania based precursor, TiO2 nanotube arrays (TNT), with the aim to prepare transparent humidity sensor. TNT were prepared by anodization of titanium thin films deposited on glass by magnetron sputtering. To obtain the thin film TNT the Ti thin films were anodized in an ethylene glycol electrolyte, containing ammonium fluoride and water until it become semi-transparent. To increase the transparency of the TNT thin films and to obtain the TiO2 anatase crystalline phase, the samples were annealed at 450°C for 2 h in air. Hydrothermal synthesis of BTO on TNT (BTO@TNT) was conducted for 2 h at 200 °C in 20 mL of aqueous solutions containing 15, 20, 30 or 40 mM Ba(OH)2. The samples were subsequently annealed in air at 450 °C for 2 h. Structural properties were investigated by XRD, SEM, EDX, TEM, HRTEM, SAED and Raman spectroscopy (RS), transparency and optical properties by UV- Vis, while humidity sensing was studied by electric measurements using impendence spectroscopy (IS). The BTO was observed by XRD and RS only in samples prepared using solutions with 30 or 40 mM Ba(OH)2. SEM measurements of that samples show nanocubes/nanoparallelepiped at the surface of TNT (Fig. 1a) indicating BTO (in cubic/tetragonal structure). In samples prepared with lower concentration of Ba(OH)2, BTO was not observed by XRD and RS, although nanoobjects containing high percentage of Ba was observed by SEM and EDS at the surface of TNT indicating unfinished reaction toward formation of BTO (Fig 1b). IS measurements show response for samples prepared with higher concentration of Ba(OH), but transparency of these samples was lower. Therefore, optimisation will be discussed in the view of structure and morphology of formed BTO@TNT.

barium titanate ; transparent titania nanotubes arrays ; SEM ; XRD ; raman spectroscopy

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