Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response

Abstract

BiFeO3 is one of the most promising multiferroic materials but undergoes two major drawbacks: low dielectric susceptibility and high dielectric loss. Here we report high in-plane dielectric permittivity (ε’ ∼2500) and low dielectric loss (tan δ < 0.01) obtained on Bi0.95Y0.05FeO3 films epitaxially grown on SrTiO3 (001) by pulsed laser deposition. High resolution transmission electron microscopy and geometric phase analysis evidenced nanostripe domains with alternating compressive/tensile strain and slight lattice rotations. Nanoscale mixed phase/domain ensembles are commonly found in different complex materials with giant dielectric/electromechanical (ferroelectric/ relaxors) or magnetoresistance (manganites) response. Our work brings insight into the joined role of chemical pressure and epitaxial strain on the appearance of nanoscale stripe structure which creates conditions for easy reorientation and high dielectric response, and could be of more general relevance for the field of materials science where engineered materials with huge response to external stimuli are a highly priced target.

Rolling dopant and strain in Y-doped BiFeO3 epitaxial thin films for photoelectrochemical water splitting

“…S2 ), for comparison purposes. As it was already observed in our previous work, the addition of the small ionic radius Y atoms to the BFO structure has a significant effect on the Y-BFO/STO thin films, especially on the “quality” of the epitaxial film expressed by its mosaic structure through crystalline lateral coherence lengths breaking 28 .…”

“…The peculiar crystallographic nanostructure of Y-BFO films with the nanostripe regions rolling throughout the film’s thickness, as revealed in the previous paper, can induce the energy band bending towards the film-electrolyte interface due to high built-in potential and mobility towards external stimuli, e.g. applied electric field, and/or incident light 28 . The evolution of PEC measured photocurrents with the epitaxial strain relaxation, in contrast with the previous published papers on undoped BFO, is presented for the first time for Y-doped BFO thin films.…”

“…To gain additional structural information about the influence of small atomic radius Y dopant, X-ray diffraction peak broadening was analyzed as a function of films thickness via Williamson-Hall-type (W-H) approaches 28 – 31 . A traditional W-H treatment applied to the 2 θ-ω scans of the symmetric (00 l ) reflections allows the extractions of the vertical correlation length (L ll ) and of the heterogeneous strain, (ε ┴ ) along the c-axis, which causes the broadness of these peaks.…”

“…In a previous paper we have emphasized the concomitant influence of small ionic radius Y 3+ doping and epitaxial strain on the dielectric behavior of BFO epitaxial thin films 28 . It was pointed out that the small ionic radius Y dopant had rolled the host BFO structure into an alternation of compressive and tensile nanostripe domain.…”

Thickness-Dependent Photoelectrochemical Water Splitting Properties of Self-Assembled Nanostructured LaFeO3 Perovskite Thin Films

“…The use of perovskite materials in solar energy harvesting by water splitting has a swift evolution lately, mainly due to the fact that the limitations of binary oxide semiconductors (TiO 2 , Fe 2 O 3 or WO 3 ), such as reduced band gap values or poor electrical charge transport properties seem to be unsolvable [ 9 , 10 , 11 ]. The possibility of tuning their intrinsic functional aspects such as dielectric, ferroelectric, or optical properties by employing strategies, such as epitaxial strain engineering or chemical doping, is the most interesting attribute of perovskite materials [ 12 , 13 , 14 , 15 , 16 , 17 ].…”