Nanoscale Structure and Mechanism for Enhanced Electromechanical Response of Highly Strained BiFeO₃ Thin Films

Abstract

The nanostructural evolution of the strain-induced structural phase transition in BiFeO 3 is examined. Using high-resolution X-ray diffraction and scanning-probe microscopy-based studies we have uniquely identified and examined the numerous phases present at these phase boundaries and have discovered an intermediate monoclinic phase in addition to the previously observed rhombohedral-and tetragonallike phases. Further analysis has determined that the so-called mixed-phase regions of these films are not mixtures of rhombohedral-and tetragonal-like phases, but intimate mixtures of highly-distorted monoclinic phases with no evidence for the presence of the rhombohedral-like parent phase. Finally, we propose a mechanism for the enhanced electromechanical response in these films including how these phases interact at the nanoscale to produce large surface strains.

Persistent Photoconductivity in Strained Epitaxial BiFeO3 Thin Films

“…4 Subsequent studies revealed that the tetragonal-like phase is actually a monoclinic phase which can be subcategorized as the M c phase. 5,6 With an increase in film thickness, another variant of monoclinic structure begins to evolve in the form of lamellas/stripes which are embedded in the matrix of the original M c phase. 5 The possibility to electrically switch between these two phases, thereby producing efficient electromechanical responses, makes the strained system of BFO a rather attractive lead-free alternative for several applications.…”

“…5,6 With an increase in film thickness, another variant of monoclinic structure begins to evolve in the form of lamellas/stripes which are embedded in the matrix of the original M c phase. 5 The possibility to electrically switch between these two phases, thereby producing efficient electromechanical responses, makes the strained system of BFO a rather attractive lead-free alternative for several applications. 7 Additionally, BFO is a wide band gap (≈ 2.7 eV) oxide semiconductor which allows electronic applications, like resistive switching.…”

Tetragonal BiFeO3 on yttria-stabilized zirconia

“…8,15,16 However, experimental results up to date have never observed a real tetragonal phase of pure BFO, or to be precise, the phase has been confirmed as a monoclinic phase with several possible space groups of Cc, Cm, Pm, or Pc symmetry. 10,12,17 Such low-symmetry phases (here labeled as tetragonal-like phase) usually serve as a structural intermediate between rhombohedral and tetragonal phases, which is easily observed in morphotropic phase boundaries (MPBs) of perovskite ferroelectrics. [9][10][11][12][13][18][19][20] structure closest to pure tetragonal has been observed in a very thin film (∼7 nm), reported by Pailloux et al 21 Another way is using the modification such as the substitution of Bi ions by Ba ions.…”

“…[1][2][3][4][5][6][7][8] Recently, through an assistance of strain engineering in thin film process, BFO exhibits a rich variety of phases including rhombohedral, monoclinic, and orthorhombic structures. [9][10][11][12][13][14] Numerous efforts have also been made to reveal the fundamental understanding of correlation between structure and electric/magnetic order parameters. In the past decade, a great research interest has notably focused on discovering the pseudo-tetragonal phase with large axial ratio (c/a) of ∼1.25 that can be only epitaxially stabilized on the substrate with compressive misfit strain greater than 4.5%.…”

Temperature-driven evolution of hierarchical nanodomain structure in tetragonal-like BiFeO3 films

“…Recently, there has been particular interest in the crystal [2][3][4][5][6][7][8] and domain structures [9,10] of the tetragonal-like (T-like) BFO thin films as well as their relationships to electric and magnetic properties [11][12][13][14][15]. The T-like BFO, which can be stabilized by strain, was theoretically predicted to have a giant polarization value of about 150 μC/cm 2 [16].…”