Interlayer strain effects on the structural behavior of BiFeO3/LaFeO3 superlattices

Artificial (BiFeO3)0.5Λ/(LaFeO3)0.5Λ superlattices have been grown by pulsed laser deposition. The periodicity Λ was varied from 150 Å to 25 Å and the relative ratio between BiFeO3 (BFO) and LaFeO3 (LFO) is kept constant in each period. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy investigations indicate antiferroelectric-like structures for large periodicity (Λ ≥ 76 Å), while Pnma LaFeO3-like structures are observed for small periodicity Λ ≤ 50 Å. Room temperature magnetic measurements were obtained by vibrating sample magnetometry and suggest antiferromagnetic ordering with weak ferromagnetism. Temperature dependent x-ray diffraction studies show an important shift of paraelectric-antiferroelectric phase transition scaling with BFO thickness. Strain and size effects explain this behavior and discussion is also made on the possible role of the oxygen octahedral rotation/tilt degree of freedom

Structural, vibrational, and dielectric investigations of Ba0.925Bi0.05(Ti0.95-x Zr (x) )Sn0.05O3 ceramics

26th International Materials Research Congress (IMRC), Cancun, MEXICO, AUG 20-25, 2017International audienceCeramics of Ba0.925Bi0.05(Ti0.95-x Zr (x) )Sn0.05O3 (0.05 x 0.30) were prepared by conventional solid-state reaction technique. The effects of the Zr4+ addition to the structural and dielectric properties were investigated. The room temperature X-ray study has allowed to evidence a tetragonal symmetry up to x = 0.10, and beyond it to a cubic single phase. Thermal dielectric study at different frequencies has revealed two different behaviors, a normal ferroelectric for x ae 0.10, and a relaxor character for the rest of the solid solution. High temperature Raman spectra corroborates the arguments of the phase transition revealed by dielectric results. In addition, a remarkable line broadening was observed in Raman spectra, which can be attributed to a certain disorder in the structure lattice. The low Zr-composition was found to exhibit a flat epsilon (r) `(T) curve with stable dielectric permittivity in a large range of temperature, promising for the X7R specifications

Resistive Switching Hysteresis in Thin Films of Bismuth Ferrite

International audienceWe have studied the resistive switching (RS) phenomenon in series of BiFeO3 thin films of thickness of 40 ? 154~nm deposited by PLD technique on conducting Nb-doped substrate of SrTiO3 and with Pt top electrodes. It was found that 154~nm film demonstrates the interface-provided I?V characteristic of Schottky diode when the applied voltage does not exceed the threshold value Vd = 1.3 V. The RS phenomenon appears as the current hysteresis loop during the 0 ? Vm ? 0 ? ?Vm ? 0 voltage sweep cycle, provided that the maximal stop-voltage Vm is larger than Vd. For thinner films neither diode-like I?V behavior nor substantial RS effect were observed. The results are interpreted in terms of the filamentary model of the mobile oxygen vacancies

Phonon and Magnon Excitations in Raman Spectra of an Epitaxial Bismuth Ferrite Film

International audienceAn epitaxial film of bismuth ferrite BiFeO3 on a MgO(001) single crystal substrate has been pre pared by pulsed laser deposition using SrTiO3 and SrRuO3 buffer layers. At room temperature, the polariza tion characteristics of the Raman spectra of the BiFeO3 film under study suggest a monoclinic symmetry. The high temperature (295\textendash1100 K) investigations of the Raman spectra have been performed in the frequency range 20 cm\textendash1 < ν < 1600 cm\textendash1. Particular attention has been paid to the high frequency region with a band observed at 610 cm\textendash1, which corresponds to the maximum density of states of the magnon branch at the Bril louin zone boundary, and an intense band in the second order Raman spectra with the maximum at ~1250 cm\textendash1, which corresponds to the density of states of two magnon excitations. It has been found that the inten sity of the band at ~1250 cm\textendash1 decreases linearly with an increase in the temperature and, above 650 K, this band is absent. The extrapolation of the temperature dependence of the integrated intensity of the band at 1250 cm\textendash1 suggests that this film undergoes an antiferromagnetic phase transition at a temperature of ~670 K