Effects of Interfaces on the Structure and Novel Physical Properties in Epitaxial Multiferroic BiFeO3 Ultrathin Films

Abstract

In functional oxide films, different electrical/mechanical boundaries near film surfaces induce rich phase diagrams and exotic phenomena. In this paper, we review some key points which underpin structure, phase transition and related properties in BiFeO3 ultrathin films. Compared with the bulk counterparts, we survey the recent results of epitaxial BiFeO3 ultrathin films to illustrate how the atomic structure and phase are markedly influenced by the interface between the film and the substrate, and to emphasize the roles of misfit strain and depolarization field on determining the domain patterns, phase transformation and associated physical properties of BiFeO3 ultrathin films, such as polarization, piezoelectricity, and magnetism. One of the obvious consequences of the misfit strain on BiFeO3 ultrathin films is the emergence of a sequence of phase transition from tetragonal to mixed tetragonal & rhombohedral, the rhombohedral, mixed rhombohedral & orthorhombic, and finally orthorhombic phases. Other striking features of this system are the stable domain patterns and the crossover of 71° and 109° domains with different electrical boundary conditions on the film surface, which can be controlled and manipulated through the depolarization field. The external field-sensitive enhancements of properties for BiFeO3 ultrathin films, including the polarization, magnetism and morphotropic phase boundary-relevant piezoelectric response, offer us deeper insights into the investigations of the emergent properties and phenomena of epitaxial ultrathin films under various mechanical/electrical constraints. Finally, we briefly summarize the recent progress and list open questions for future study on BiFeO3 ultrathin films.

Thickness-Dependent Evolution of Piezoresponses and Stripe 90° Domains in (101)-Oriented Ferroelectric PbTiO3 Thin Films

“…On the one hand, although misfit dislocations evolve at the PTO/LSAT(101) interfaces (Figure a), the PTO film near the interface is still not fully relaxed because of the gradual relaxation as shown in Figure d, which promotes the formation of c domains with out-of-plane components of polarization vectors, such as the present c 1 / c 2 domains. On the other hand, the stability of domain structures in ferroelectric films also depends on the electrostatic boundary conditions. , If the film has a uniform out-of-plane polarization, it will bring a large depolarization field, which could be reduced or screened by free charges from metallic electrodes, adsorbed ions, ionic point defects on the ferroelectric film surface, reduction of ferroelectric polarization, polarization rotation toward in-plane direction, or by formation of domains with inverse out-of-plane components of polarization vectors. , In the present work, the formation of alternating c 1 / c 2 domains exhibiting alternate upward and downward P s (Figure f) reduces the depolarization field in PTO films, which is similar to the formation of 109° domains in (001)-oriented BiFeO 3 films . Our experiment results are also consistent with previous theoretical calculations that c 1 and c 2 domains with out-of-plane components of polarization vectors are stable under large compressive strains …”

Surface Modification and Enhancement of Ferromagnetism in BiFeO3 Nanofilms Deposited on HOPG

“…Recently, the demand for the use of multiferroics in various fields and products of nanoelectronics has been growing steadily. One of the most interesting compounds in the form of a thin film is bismuth ferrite (BFO) because of its electric [ 1 ], magnetic [ 2 ], piezo [ 3 , 4 ], ferroelectric [ 5 ], dielectric [ 6 ], memristive [ 7 , 8 ] and optical [ 9 , 10 , 11 , 12 ] properties. In addition, BiFeO 3 /reduced graphene oxide composites have excellent photocatalytic characteristics due to improved light absorption, an increase in the number of reactive centers and a low rate of recombination of electron–hole pairs [ 13 ].…”

Ferroelectric monoclinic phases in strained K0.70Na0.30NbO3 thin films promoting selective surface acoustic wave propagation

“…[120][121][122] However, the amount of experimental studies available is still comparably low: (Sr,Ba)TiO 3 , [123] BaTiO 3 , [124] BiFeO 3 . [119,125] On the one hand, this lack of experimental studies might be caused by the low availability of suitable substrate materials, which allow for a systematic tailoring of strain conditions. On the other hand, the profound and fun-7.1.…”