Highly (001)-Textured Tetragonal BiFeO 3 Film and Its Photoelectrochemical Behaviors Tuned by Magnetic Field Haomin Xu, † Yuanhua Lin,* ,† Takashi Harumoto, ‡ Ji Shi,* ,‡ and Cewen Nan † † State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, People’s Republic of China ‡ Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8552, Japan * S Supporting Information ABSTRACT: Highly (001)-textured BiFeO 3 film in tetragonal phase (T-BFO) with a giant c/a ratio was first obtained on quartz/polycrystalline ITO substrate. Our results indicate that the polycrystalline ITO layer with small surface roughness is a critical point to control the growth of T-BFO structure. It should be ascribed to the fact that a Bi-rich phase interlayer (∼5 nm) could be formed on ITO, which acted as a crystal seed layer and thus induced the growth of (001)-textured T-BFO structure. The observed weak room temperature ferromagnetism should be attributed to Fe valence change. Open circuit potential measurements under 360 μW/cm 2 full spectra irradiation show that the open circuit potential and the lifetime of photo-induced carriers increased under applied magnetic field, which reveals that the applied magnetic field can manipulate the photo electrochemical behaviors of BFO film. Our findings offer a simple way to fabricate highly (001)-textured T-BFO film, which make it desirable to obtain extensive applications for these oriented BFO films. KEYWORDS: tetragonal BiFeO 3 , polycrystalline substrate, magnetic controlled, photo-induced electron, lifetime ■ INTRODUCTION Bismuth ferrite (BiFeO 3 , BFO) has been widely studied as a room temperature single phase multiferroic material (T c ∼ 1103 K, theoretical polarization is around 100 μC/cm 2 at room temperature (RT), T N ∼ 647 K, G-type antiferromagnetic structure, display week ferromagnetism in RT due to 62 nm spin). 1-3 In the past decades, the ferroelectric and ferromagnetic properties of BFO have been widely studied. 4-6 Meanwhile, BFO is also a chemically stable semiconductor with small band gap (2.1-2.7 eV), and has been proven to have intriguing photoferroelectric, photocatalytic, and photoelec- trochemical (PEC) properties. 7-11 All the findings imply the promising potential applications of BFO films in the fields of energy conversion, environmental protection, and multifunc- tional electric device manufacture, and it is of great significance to further study the interaction between multiferroic and photoinduced properties of BFO. It has been found that the properties including ferroelectric, antiferromagnetic, and photo- electric properties of BFO films are highly sensitive to the film texture as well as the phase composition. For example, up to now, it has been proved that (001)-oriented tetragonal BFO (T-BFO) performs better electronic properties; R-BFO and T- BFO has different band gaps; crystal and domain orientation of BFO can cause spatial selective of the photochemical activity. 12-16 All of these results show that it makes great sense to further study the textured BFO as well as its properties. Generally, in conventional ways only on textured bottom layer can textured BFO layers grow, which require high cost single crystal substrates or complex fabrication process. 1,4,17 Chemical solution deposition is one of the most commonly used chemical methods, still needing single crystal substrates or a seeding layer. 18,19 It is of great importance to find a way to obtain textured BFO films much more easily and with lower cost. Among all the phases existing in the epitaxial BFO thin films, the tetragonal phase with giant c/a ratio is of particular interest as it was predicted to exhibit giant polarization of around 150 μC cm -2 due to first principles calculation (FPC). It is predicated that this kind of BFO phase is a stable state and could be formed on polycrystalline substrates with the presence of a properly controlled buffer layer, and it is worthwhile to figure out a way to implement this predicition. 20-22 In this paper, we used the metal oxide Sn-doped In 2 O 3 (ITO) as the conductive bottom layer, low cost high-temperature quartz as the substrates, and successfully fabricated BFO films with (001)-preferred orientation in tetragonal phase with a giant c/a ratio around 1.22. People have studied PEC properties and external electric field controlled PEC properties (i.e., the polarization effect on PEC properties) of T-BFO before, 23 but few studies about magnetically controlled PEC behaviors have been reported due to the equipment limit especially the Received: May 30, 2017 Accepted: August 17, 2017 Published: August 17, 2017 Research Article www.acsami.org © 2017 American Chemical Society 30127 DOI: 10.1021/acsami.7b07644 ACS Appl. Mater. Interfaces 2017, 9, 30127-30132