Mild hydrothermal synthesis of BiFeO₃ films on BiFeO₃ seed-layer-coated indium tin oxide substrates and their piezo-related applications

This paper reports the development of a facile hydrothermal approach to grow pure BiFeO₃ (BFO) films on BFO seed-layer-coated indium tin oxide/glass substrates in mild conditions. The results indicate that the seed layer and no involvement of complex agents were crucial for the mild condition [small amount of NaOH (approximately 1 g); 180 °C] because of homogeneous nucleation and growth of the BFO films. The phase and crystallinity of the BFO films were studied through X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction. The stoichiometric BFO films were ascertained using electron-probe energy-dispersive spectroscopy. The band gap of the BFO films was approximately 2.6 eV. The induced piezopotential of approximately 2.0 mV at a stress of approximately 0.6 GPa indicated the piezoelectric property of the obtained BFO films. The associated piezotronic properties were determined from the asymmetric current–voltage characteristics. The piezophotocatalytic efficiency for methylene blue degradation under visible light irradiation was approximately three times higher than for photocatalysis without stress.