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Structural and electrical properties of hydrothermally synthesized BaTiO3 and BaTiO3/TiO2 nanostructures

BaTiO3 (BTO), is a well-known and widely investigated dielectric material. It is mainly used in capacitors due to its high dielectric constant. The dielectric properties of BTO are controlled by purity and microstructure which are dependent on the methods of preparation. Recent advances in nanotechnology such as MLCC, MEMS, DRAM have resulted in miniaturization of devices [1, 2]. In this work barium titanate nanostructures were synthesized by hydrothermal processing of titanium based precursor in aqueous solution of BaCl2 and NaOH. Several titanium based precursors were used: TiO2 nanopowder, titanate nanotubes (H2Ti3O7), and TiO2 nanotubes array prepared by anodisation of titanium foils. Structural and compositional properties were investigated by XRD, SEM, EDX, TEM, HRTEM, SAED and Raman spectroscopy (ex–situ and in-situ), while electric measurements were studied by impendence spectroscopy. In the case of synthesis from TiO2 nanopowder precursors, obtained BaTiO3 nanoparticles were found to be about 50 nm in size (Fig. 1a and 1b), while in the case of H2Ti3O7 nanotubes precursor the average size of the particles are somewhat larger. In both cases TiNT, homogenous particles in tetragonal phase were formed. In the case of hydrothermal treatment of TiO2 nanotubes array precursor (Fig. 2a), BaTiO3/TiO2 composites were obtained, where BTO formed the film at the TiO2 nanotubes array (Fig. 2b). Tetragonal phase of BFO, having 4mm symmetry with c/a axis ratio close to one, is hard or impossible to distinguish from cubic phase by using standard diffraction techniques, so the phase purity and the structure were studied by Raman spectroscopy (RS) as a main technique [3]. In situ low and high temperature RS was used for study of ferroelectric phase transitions from tetragonal to cubic phase. TEM and HRTEM techniques were used to study structure and morphology of all prepared samples. The surface electrical conductivity (Fig. 3a and 3b) and dielectric constant will be discussed in the relation to RS measurements.

BTO-TiO2 heterostructure; persistent photoconductivity; phase transitions

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