Temperature‐dependent Raman scattering studies of polycrystalline BiFeO₃ bulk ceramics

Abstract

This work reports the temperature-dependent Raman scattering study of mutiferroic BiFeO 3 (BFO) bulk ceramics in a wide temperature range of 93-843 K. The polycrystalline samples are sintered at four different temperatures and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry, differential scanning calorimetry (DSC), and optical microscopy. The microstructure shows remarkable changes in terms of grain size and domain pattern as the sintering temperature increases. The DSC curves show prominent exothermic peaks at 645 K, the antiferromagnetic-paramagnetic phase transition temperature. The Raman spectra of all the four specimens reveal strong anomalies in the vicinity of the Neel temperature, which can be attributed to the multiferroic nature of BFO. The Raman scattering studies also reveal considerable spectral changes at a temperature range of 140-200 K in all the specimens, which can be inferred to a further spin-reorientation transition exhibited in BFO at a cryogenic temperature.

Dielectric anomalies due to grain boundary conduction in chemically substituted BiFeO3

“…From Figure 4(a), we can observe the following features in Raman spectra with increase of temperature: (i) reduction in the peak intensity, (ii) lower frequency values (see dotted line in Figure 4(a)), (iii) marked widening of the peaks, and (iv) pronounced decrease in the intensity of Raman modes (this effect is more pronounced in high wavenumber peaks (>400 cm À1 ), which disappears near T N $ 620 K). Similar observations were reported by other researchers in bulk and single-crystal BFO, 25,48,50 and they attributed this effect to thermal broadening and thermal disorder.…”

“…Table III. From this table, we can observe that a similar number of modes were reported for BFO at 93 K and at RT by Kothari et al 46 and Rout et al 25 It was noted that the Raman spectra of BNFM at low temperature (83 K) and RT (Figure 4(a) and Table III) are very similar, supporting the idea that the rhombohedral (R3c space group) structure is retained in Nd, Mn co-doped BFO ceramics; similar results were obtained by Haumont et al 48 for BFO single-crystals. Singh et al 49 have reported A 1 and low frequency E modes corresponding to Bi-O bonds, whereas higher frequency E modes are related to Fe-O bonds.…”

“…In these XRD patterns, no extra splitting can be observed in characteristic rhombohedral peaks; thus, it can be concluded that there is no phase transition occurring from rhombohedral to tetragonal or other phases with co-doping of Nd and Mn in A and B sites of BFO. 25 Most of the diffraction peaks in this XRD pattern of BNFM shift slightly towards higher angle compared to those of BFO due to slight lattice compression by chemical doping of Nd and Mn at A and B sites. The Rietveld refinement of BNFM ceramics has been carried out by considering the rhombohedrally distorted perovskite structure with space group R3c, initial lattice parameters and atomic positions for the simulation were taken from those reported elsewhere.…”

Structure, magnetic, and thermal properties of Nd1−xLaxCrO3 (≤x≤1.0)

“…Similar observations have been reported for some other perovskite compounds. [22][23][24][25] Features of the B 2g ͑7͒, A g ͑4͒, and A g ͑3͒ modes are associated with the vibration of oxygen ions. Their frequencies decrease with increasing La content, because of the increase in the RE-O and Cr-O force constants.…”

Spin and lattice excitations of aBiFeO3thin film and ceramics

“…Probing IR-active low-energy excitations is hindered by a lack of sufficiently large single crystals. Raman-active phonons of the rhombohedral R3c BiFeO 3 structure have been reported for single crystals, [6][7][8] polycrystalline ceramics, [9][10][11] and thin films, 12,13 however, there is a significant discrepancy between the claimed phonon frequencies and symmetry representations. A possible explanation for such inconsistences between the various experimental results is the presence of oblique phonon modes, which show a continuous variation of frequency along the phonon propagation vector with respect to the crystallographic axis of the probed specimen.…”