Realization of rhombohedral, mixed, and tetragonal like phases of BiFeO3 and ferroelectric domain engineering using a strain tuning layer on LaAlO3(001) substrate

Abstract

BiFeO3 (BFO), a room temperature multiferroic, undergoes a series of structural transformations under varying strain conditions by utilizing appropriate substrates for a specific strain condition. In this study, epitaxial thin films of BFO were grown on La0.7Sr0.3MnO3±δ (LSMO), a strain tuning layer on LaAlO3[LAO (001)] substrates, using pulsed laser ablation. LSMO layers of varying thicknesses from 2 nm to 20 nm were grown followed by a BFO layer of a fixed thickness (20 nm). A strained layer of ∼2 nm thick LSMO stabilizes the tetragonal like phase of BFO. Increasing the thickness of the LSMO layer to 10 nm results in a mixed phase with rhombohedral (R) and tetragonal (T) domains, and a further increment of the LSMO layer thickness to 20 nm stabilizes the rhombohedral phase of BFO. The tetragonal phase with weak monoclinic distortion possessed 180° domains with dominant out-of-plane polarization components. However, the mixed phase (R + T) possessed various plausible polarization components in both out-of-plane and in-plane directions. Further, a thermodynamically consistent model based on the phase field approach was implemented to investigate the role of strain on the formation of domain patterns with various polarization components and piezoelectric coefficients. The simulated domain structure exhibited a similar transformation on the dominant polarization components as observed in experiments across different phases of BFO. Our simulations show that the elastic constraint along the z-direction enhances the tetragonality of BFO. The piezoelectric (d33) coefficient was found to be ∼46 pm/V for the 20 nm mixed phase BFO, which was nearly a 200% increment compared to the single phase BFO thin films on LAO.

Metastable Tetragonal BiFeO3 Stabilized on Anisotropic a-Plane ZnO

“…Our results firmly show that the strain engineering of BFO is not only limited to the isotropic conditions but also can be extended to the vast anisotropic strain region. For instance, alloying with CdO is effective in tuning the lattice constants of ZnO, which may favor the T–R transition through strain engineering . Furthermore, the stress-induced phase transition has been reported in a variety of materials, , and the anisotropic strain engineering proposed here offers an alternative pathway for phase manipulations and function designs in these systems.…”

Domain wall-localized phonons in BiFeO3: spectrum and selection rules

“…The parameters of the model were adopted from ref. 43 . To obtain the equilibrium configuration, we minimize the free energy R fd 3 r in Eq.…”

A phase field model combined with genetic algorithm for polycrystalline hafnium zirconium oxide ferroelectrics

“…We introduce a set of displacements to solve the heterogeneous strain such that δ ij = 1/2(u i,j + u j,i ). The mechanical equilibrium condition given by σ ij,j = 0, is solved using the phase field microelasticity method [45][46][47] (explained in the Supporting Information, Section S1). We do not solve elastic energy in the three dimensional GA calculations because of it's complexity and high computational cost.…”