Nanoscale Switching Characteristics of Nearly Tetragonal BiFeO₃ Thin Films

Abstract

We have investigated the nanoscale switching properties of strain-engineered BiFeO 3 thin films deposited on LaAlO 3 substrates using a combination of scanning probe techniques. Polarized Raman spectral analysis indicate that the nearly-tetragonal films have monoclinic (Cc) rather than P4mm tetragonal symmetry. Through local switching-spectroscopy measurements and piezoresponse force microscopy we provide clear evidence of ferroelectric switching of the tetragonal phase but the polarization direction, and therefore its switching, deviates strongly from the expected (001) tetragonal axis. We also demonstrate a large and reversible, electrically-driven structural phase transition from the tetragonal to the rhombohedral polymorph in this material which is promising for a plethora of applications.

Crystallization engineering as a route to epitaxial strain control

“…When grown on (001)LaAlO 3 by PLD, due to a high lattice mismatch and corresponding epitaxial strain, BiFeO 3 becomes tetragonal and exhibits a different ferroelectric behavior than its rhombohedral modification. 16 In our case, however, we show that epitaxial BiFeO 3 films produced by ALD and subsequent annealing on (001)LaAlO 3 exhibit a strain relaxation and periodic misfit dislocations not present in epitaxial films formed by higher temperature methods, where crystallization occurs during deposition. Because in the ALD experiments, Bi-Fe-O thin films are grown from metal-organic precursors, they typically contain carbon atoms as impurity species.…”

Electric control of straight stripe conductive mixed-phase nanostructures in La-doped BiFeO3

“…This is a different feature from the pure BFO, in which the out-of-plane PFM shows a strong signal at the phase boundaries rather than the Electric control of straight stripe conductive mixed-phase nanostructures K-E Kim et al constituent phase areas. 29 The R 0 -phase region exhibits an B15% higher out-of-plane piezoresponse than the T-phase region. With the assumption that the piezoresponse is proportional to ferroelectric polarization, it is presumed that the ferroelectric polarization of T-phase (P T ) within the mixed-phase area has a magnitude of B120 mC cm À2 and orients itself to a direction rotated by a polar angle of 151 from the normal and by an azimuthal angle of 301 from an in-plane direction o1004.…”

Prediction of variation in d-orbital occupancy in strain induced tetragonal phase of BiFeO3 thin film

“…Due to thermal expansion and lattice mismatch between the BFO film and the substrates, different states of compressive or tensile strains can be generated by employing different substrates, resulting in different structural phases, from rhombohedral like monoclinic phase or tetragonal-like monoclinic phase, to a fully relaxed bulk like rhombohedral one. [30][31][32][33][34][35][36][37][38][39][40][41] One of the most promising findings is the prediction of a metastable state in strained BFO thin film with P4 mm symmetry. [42][43][44][45][46][47][48] Out of the variety of above reported phases, we considered the strain induced tetragonal (P4mm) (T) phase in BiFeO 3 (BFO) observed in thin films on an STO (001) substrate having the misfit strain ∼1.4% in our first principles study.…”