Ferroelectric BaTiO3/BaZrO3 superlattices: X-ray diffraction, Raman spectroscopy, and polarization hysteresis loops

Abstract

Artificial superlattices (SLs) consisting of ferroelectric BaTiO3 (BT) and paraelectric BaZrO3 (BZ) have been growth by a pulsed laser deposition technique. The epitaxial BT and BZ layers with a periodicity from 16 Å to 1056 Å were sequentially deposited on (001) MgO substrate buffered with an oxide conducting layer of La1/2Sr1/2CoO3. The out-of-plane lattice parameters of the SLs constituents were determined by modeling of the x-ray diffractograms. The results indicate that the polar c-axis of the BT layers lies in the plane of the substrate and BZ layers exhibit enhanced tetragonal distortion which is induced by the mismatch between the alternating BZ and BT layers. The Raman data reinforces this interpretation and suggest a monoclinic phase in BT layers and polar phase in BZ layers. The Raman spectra give evidence of coupling between the constituent layers and a narrowing of the Raman peaks is attributed to a reduction in the disorder of the Ti4+ ions due to the epitaxial strain. This strain is responsible for the upward frequency shift in the soft modes, especially, the E(1TO) mode, which is markedly altered with respect to its analogs in BT-bulk crystal and BT thin film. Ferroelectric hysteresis loops measurements, confirmed the x-ray diffraction and Raman results, and revealed a clear ferroelectric behavior for the constrained SLs (32 Å≤Λ≤256 Å) while a weak ferroelectricity is observed for the large periods (Λ=500 Å and 1056 Å). This is attributed to the strain-induced ferroelectricity in BZ layers for the constrained SLs.

Phase Diagram of BiFeO3/LaFeO3 Superlattices: Antiferroelectric‐Like State Stability Arising from Strain Effects and Symmetry Mismatch at Heterointerfaces

“…Using the Bragg formula for SLs we have calculated an average out-of-plane lattice parameter for each superlattice from the 2 value of the most intense satellite peak. [9][10][11][12][13][14][15] These results are presented in Figure 1 and show a linear decrease of the average out-of-plane lattice parameter with increasing x. Such gradual behaviour has also been observed for out-of-plane lattice parameter of Bi 1-x La x FeO 3 single films.…”

“…[8] According to this model competing distortion and octahedral tilt ordering (a such as superconductor/ferromagnetic, relaxor/ferroelectric and paraelectric/ferroelectric. [9][10][11][12][13][14][15][16] In particular polarization rotation has been observed along with a MPB in PbTiO 3 /CaTiO 3 superlattices. [16] In this work we have artificially introduced competition between R3c and structural behaviour that strongly depends on the composition and temperature.…”

“…Structural competition at the 5 interfaces is probed via the synthesis of superlattices with varying ratio of BFO and LFO in the period ((BiFeO 3 ) (1-x) /(LaFeO 3 ) x with =8-9nm kept fixed and x varying from 0.25 to 0.8 with a total of 25 bilayers). For instance the superlattice BFO 0.5 /LFO 0.5 shows the same ratio of BFO and LFO in the period (same thickness of about 4-4.5nm half the wavelength/periodicity ; similar notation/terminology were used in references [10][11][12][13][14][15]. The architectures of the two sets of SLs are given in the supporting information.…”

Strain analysis of multiferroic BiFeO3-CoFe2O4 nanostructures by Raman scattering

“…[10][11][12][13][14][15] Most Raman scattering studies of composite-type thin films in the literature concern thin film superlattices. [16][17][18][19] Micro-Raman spectra were recorded using a 488.0 nm laser line through a LabRam…”

Characteristics of BaTiO 3 /(Ba,Sr)TiO 3 Superlattices Synthesized by Pulsed Laser Deposition

“…2 uc/2uc). Similar studies were carried out in other 293 systems, such as: BT/BaZr0 3 [5], PbZr0 3 /PbTi0 3 [6], PbZr0 3 /BaZr0 3 [7]. However few studies have been done to study the effect of manipulation of the degree of strain by changing the composition of one of the constituents of the SLs and investigate the effect on their structural, electrical, and ferroelectric properties.…”