Structural Characterization of BiFeO₃ Thin Films by Reciprocal Space Mapping

Abstract

High-resolution X-ray diffraction reciprocal space mapping (HRXRD-RSM) was applied for the structural characterization of epitaxial BiFeO3 thin film grown on SrRuO3-coated (001) SrTiO3 single crystal substrate with a variety of film thicknesses ranging from 15 to 500 nm. Distinguishing monoclinic structure from rhombohedral or tetragonal structures was accomplished with a set of HRXRD-RSMs measured for several hkl diffraction conditions. The BiFeO3 thin films showed both monoclinic and tetragonal structures depending on film thickness. Tetragonal structure was observed for film thicknesses below 50 nm and was highly strained due to epitaxial strain, while films with film thickness thicker than 50 nm showed monoclinic structure. No BiFeO3 thin films showed bulk rhombohedral structure. This structural change in BiFeO3 thin film may play an important role in the enhanced ferroelectricity observed.

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

“…Both our results and the results of previous works focusing on this R-phase (Ref. [25,26,27]) reveal similar lattice parameters and monoclinic distortions. RSM of the 001-diffraction condition of this film (Fig.…”

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

“…An insulating band gap of 2.6 eV was obtained consistent with the range of band gaps (1.7-2.7 eV) obtained for bulk BFO. 43 The magnetic moment on Fe atom was found to be 4.13µ B close to the experimentally observed value of 3.75 µ B 65 and that on oxygen and bismuth was 0.04µ B and 0.004µ B respectively. The net magnetic moment per magnetic sublattice was found to be 3.96µ B .…”

“…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.…”

Untilting BiFeO3: The influence of substrate boundary conditions in ultra-thin BiFeO3 on SrTiO3

“…In particular, ultra-thin BiFeO 3 films grown on (001) SrTiO 3 substrates with a SrRuO 3 buffer layer showed evidence for a transition to tetragonal symmetry. 11,18,19 Also, it has been reported that BiFeO 3 films grown on (001) SrTiO 3 can have a tetragonal structure with a giant c/a ratio, resulting from the higher strain induced by a Bi 2 O 3 layer, which can be formed between the film and the substrate. 20 In this paper, we report on the thickness dependence of the BiFeO 3 thin film structure in the ultra-thin regime under moderate compressive strain from (001) SrTiO 3 substrates.…”