A facile synthesis of Al-doped BaTiO3 thin films by a hydrothermal-galvanic couple method on TiAlN film electrodes

Abstract

Al-doped barium titanate (ABT) thin films were produced by a facile hydrothermal-galvanic couple (HT-GC) method using ternary TiAlN seeding layers. TiAlN thin films serving as the working electrode were deposited onto Si substrates by reactive unbalanced magnetron sputtering. HT-GC synthesis was conducted in the alkaline solutions consisting of 0.5 M Ba(CH3COOH)2 and 2 M NaOH. Although no external power sources were applied, substantial galvanic currents occurred during the synthesis. X-ray diffraction patterns show that cubic ABT films were formed over TiAlN. Field-emission scanning electronic microscopy revealed ABT films exhibiting hemispherical grains over the nitride surface with single-layered structures. X-ray photoelectron spectroscopy verified Al doping in the obtained ABT coatings. Reaction paths and formation mechanisms of the ABT coatings were also proposed. Moreover, the ABT thin films possessed higher residual polarization (Pr) and piezoelectricity coefficient (d33) compared with un-doped BaTiO3 (BTO), deduced from polarization–electric field loops results. The deduced Pr-value for BTO thin films was 0.8 μC/cm2 and could be enhanced to 1.6 μC/cm2 for ABT thin films, meanwhile the value of d33 for BTO films was 13 ± 1 pC/N and increased to 18 ± 1 pC/N for ABT films. Such a facile synthesis of ABT thin films may bring in more technological applications such as piezoelectric and triboelectric materials in the hybrid nanogenerator, and non-volatile ferroelectric random access memory.