We report the synthesis of undoped and Sc3+-doped BiFeO3 nanoparticles using the sonochemical technique.
X-ray diffraction reveals that all samples are single phase with no
impurities detected. EDX analysis was done to confirm the extent of
Sc3+ doping in the samples. The size and morphology of
the nanoparticles have been analyzed using transmission electron microscopy
(TEM). XPS studies were done to check the presence of Fe2+ ions in the samples. The BiFeO3 nanoparticles show a
weak ferromagnetic behavior at room temperature, which is quite different
from the linear M–H relationship
reported for bulk BiFeO3. The substitution of Sc ions for
Bi enhances the ferromagnetic as well as ferroelectric properties
of this system, which is mainly attributed to the antiferromagnetic
core and ferromagnetic surface of the nanoparticles, together with
the mild structural distortion. Temperature and field dependence of
magnetization curves reveal the frustrated magnetic behavior of this
system. The leakage current is considerably reduced, and electric
polarization increases significantly in the case of BiFe0.95Sc0.05O3 nanoparticles. Magnetoelectric coupling
was observed in the BiFe0.95Sc0.05O3 sample. Thus, it can be inferred that Sc3+-doped BiFeO3 nanoparticles show promise as good multiferroic materials.
This paper introduces a new robust method for the removal of background tissue fluorescence from Raman spectra. Raman spectra consist of noise, fluorescence and Raman scattering. In order to extract the Raman scattering, both noise and background fluorescence must be removed, ideally without human intervention and preserving the original data. We describe the rationale behind our robust background subtraction method, determine the parameters of the method and validate it using a Raman phantom against other methods currently used. We also statistically compare the methods using the residual mean square (RMS) with a fluorescence-to-signal (F/S) ratio ranging from 0.1 to 1000. The method, 'adaptive minmax', chooses the subtraction method based on the F/S ratio. It uses multiple fits of different orders to maximize each polynomial fit. The results show that the adaptive minmax method was significantly better than any single polynomial fit across all F/S ratios. This method can be implemented as part of a modular automated real-time diagnostic in vivo Raman system.
Ferroelectric thin films of BaxSr1−xTiO3 with compositional gradients normal to the growth surface have been formed by the successive deposition and annealing of films having step-variable Ba to Sr ratios. By suitably tailoring the magnitude and sense of the gradient in Ba to Sr ratio, directional potentials can be built into the structures yielding a new, but controllable, hysteresis phenomenon. Slater’s empirical model for ferroelectric materials has been extended to also describe thin films with polarization gradients normal to the growth surface, i.e., graded ferroelectric devices. This model accounts for several aspects of these structures, including: the broadness of the permittivity plots with temperature, the formation of a spontaneous potential upon oscillatory field excitation, offsets in the hysteresis graphs along the displacement axis with directions which are gradient dependent, and the electric field dependence of that offset.
Structural and magnetic properties of polycrystalline BiFeO3, Bi0.9Ca0.1FeO2.95, Bi0.9Ba0.05Ca0.05FeO2.95, and Bi0.9Ba0.1FeO2.95 ceramic samples were studied to establish the effects of doping in BiFeO3 on the magnetic property. X-ray diffraction data of the undoped and doped BiFeO3 samples were refined to a rhombohedral structure with space group R3c. X-ray photoelectron spectroscopy study showed the formation of a single-phase in both the undoped and doped BiFeO3 ceramics with Fe in the 3+ valence state. Ca doped and Ba-Ca co-doped BiFeO3 ceramic samples show weak ferromagnetic ordering at room temperature. This observation makes Ca doped and Ba-Ca co-doped BiFeO3 samples an interesting material system for magnetoelectric coupling studies.
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