High pressure Raman investigations of multiferroic BiFeO₃

Abstract

We have reported a Raman scattering investigation of bismuth ferrite (BiFeO(3)) under high pressure up to 50 GPa. Distinct changes in the Raman spectra show evidence for three pressure-induced structural transitions. The abrupt frequency redshifts of the Raman modes near 300 cm(-1) at around 3 GPa are attributed to the modulation of the FeO(6) octahedral tilts. The disappearance of the modes below 250 cm(-1) at 8.6 GPa, together with the enhancement of the two modes in the range of 300-400 cm(-1), indicate the phase transition from the rhombohedral to orthorhombic symmetry. Afterward, the E-3 and E-4 modes disappear at 44.6 GPa, pointing to the occurrence of the orthorhombic-cubic phase transition, which is consistent with the previous postulate that an orthorhombic-cubic transition takes place across the metal-insulator transition at high pressures.

Multiple high-pressure phase transitions in BiFeO3

“…Very recently, Kozlenko et al [49] have reported a powder neutron diffraction study and identified a high-pressure orthorhombic phase with space group P bam between 3 and 8.6 GPa, distinct from the phases previously seen. In parallel, Raman spectroscopy has also been used to investigate phase transitions [37,44]. Both studies revealed two phase transitions in the low-pressure range, but at somewhat different pressures, about 3 and 9 GPa.…”

“…Despite literature re- ports on the effect of high-pressure on BFO, the actual symmetries in the low-pressure regime remain controversial and the very-high pressure regime has not been properly investigated (see ref. [37][38][39][40][41][42][43][44][45] and following section). Here, we investigate BFO by using Raman spectroscopy and synchrotron X-ray diffraction on both powder and single crystals up to the very high-pressure of 55 GPa, a regime only rarely explored in functional oxides beside some notable exceptions [12,39,46,47].…”

Pressure induced para-antiferromagnetic switching in BiFeO3–PbTiO3 as determined using in-situ neutron diffraction

“…An orthorhombic-cubic transition was observed at 44.6 GPa using Raman scattering. 17 A study of PbTiO 3 showed a number of structural phase transitions above 11 GPa. 18 Ahart 19 and Wu 20 showed the presence of a morphotropic phase boundary for PbTiO 3 as a function of pressure, with passage from tetragonal at low pressure to rhombohedral at high pressure, with an intermediate monoclinic phase.…”

Improved magnetization and reduced leakage current in Sm and Sc co-substituted BiFeO3

“…30 The E mode at 276 cm À1 in BFO shifts to 278 cm À1 indicates destabilization of B-site cations due to the change in internal chemical pressure with the substitution of Sc which in turn causes octahedral tilts 8,31 and hence leads to the structural changes. The co-substitution of Sm and Sc causes disorder in their respective sites which are reflected in terms of increase in the FWHM of Raman modes.…”

“…The decrease in the dielectric constant in the BSFSO compound indicates the reduction of the oxygen vacancies upon substitution. 31 The reduction of oxygen vacancies with the substitution of Sm and Sc in BFO is anticipated because of stronger bond enthalpy of Sm-O and Sc-O bonds, respectively, than that of Bi-O and Fe-O bonds. 26 …”