Structural, magnetic, vibrational and impedance properties of Pr and Ti codoped BiFeO3 multiferroic ceramics (original) (raw)
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Structural, magnetic and dielectric properties of Pr-modified BiFeO3 multiferroic
JALCOM (2013)
The structural, vibrational, magnetic and dielectric properties of polycrystalline BiFeO3 and Bi0.95Pr0.05FeO3 are investigated by combining X-ray diffraction, Raman scattering spectra, magnetometry and dielectric measurements. Structural symmetry with rhombohedral R3c phase is revealed for both parent and 5% Pr substitution at Bi site, serving no chemical pressure and causes no structural transition from R3c to any other phase is identified from x-ray diffraction patterns and Raman scattering spectra. The shifting of phonon modes towards higher frequency side is attributed to lower atomic mass of Pr ion as compared to Bi ion. The magnetic measurements at room temperature indicate that Pr substitution induces ferromagnetism and discerns large and non-zero remnant magnetization as compare to pristine BiFeO3. Both dielectric permittivity and loss factor of Bi0.95Pr0.05FeO3 strongly decreases with increased frequency. Significant role of hopping of oxygen ion vacancies in Bi0.95Pr0.05FeO3 is inferred from modulus spectra and ac conductivity analysis.
Journal of Alloys and Compounds, 2018
In this work, a few compositions in the system (1-x) BiFeO 3-(x)Pb(Zr 0.52 Ti 0.48)O 3 named as (1-x)BFO-(x)PZT with range 0.0 ≤ x ≤ 0.40 were synthesized by sol-gel route. Rietveld analysis of X-ray diffraction data has revealed single phase formation of all these compositions. An effort has been made to correlate the results using our studies on microstructural, electrical and optical properties of solid solution compounds. Temperature dependent dielectric constant and loss has been found to be improved with increasing dopant concentration (PZT) in BiFeO 3. Temperature dependent conductivity behavior revealed that an Arrhenius type of thermally activated process in the low temperature region, followed by small polaron hopping and oxygen vacancy (singly and doubly) at intermediate and high temperature. Optical studies showed absorption of light in the visible region, with a blue shift in energy band gap with increasing concentration of PZT in BiFeO 3 ceramics. Fourier transform infrared spectra showed that strong band corresponds to the Fe-O stretching and O-Fe-O bending vibrations.
Effect of Pr substitution on structural and electrical properties of BiFeO3 ceramics
Material Chenistry and Physics
"Investigation on structural, vibrational, dielectric and ferroelectric properties of Bi1xPrxFeO3 (x ¼ 0.0, 0.15, 0.25) ceramic samples has been carried out. Room temperature Rietveld-refined X-ray diffraction pattern shows the crystal structure of Bi1xPrxFeO3 is rhombohedral for x ¼ 0 and triclinic for x ¼ 0.15, 0.25. The changes in Raman normal modes with increasing doping concentration infer the structural transformation is due to Pr substitution at A-site in BiFeO3. Raman spectra also reveal suppression of ferroelectric behavior due to Pr doping. The dielectric parameters, namely, dielectric permittivity (ε0) and loss tangent (tan (d)) were evaluated as a function of frequency at room temperature. The ferroelectric polarization reduces in Pr doped bulk BFO samples due to structural change."
Journal of Alloys and Compounds, 2010
The role of doping Ta in Fe-site on the phase, microstructure and dielectric properties of Bi 0.8 La 0.2 FeO 3 (BLFO) has been investigated in this research. Single phase Bi 0.8 La 0.2 Fe 1x Ta x O 3 (BLFTO) ceramics with x = 0.0, 0.01, 0.03 and 0.05 were synthesized by conventional solid-state reaction method. The BLFTO dried pellets were calcined at 800 o C for 2 hours and then sintered at 1000 o C for 2 hours. Phase analysis by X-ray diffraction (XRD) indicated formation of single phase distorted R3c structure. Microstructural investigation using the field emission scanning electron microscope (FESEM) showed that addition of Ta dramatically reduced the average grain size of Bi 0.8 La 0.2 FeO 3 due to its strong pinning effect from 10.6 µm in Bi 0.8 La 0.2 FeO 3 to 0.92µm in Bi 0.8 La 0.2 Fe 0.95 Ta 0.05 O 3. Ta doped BLFO showed superior values of dielectric constant (> 2000) at room temperature. At higher temperature a considerable increase in the dielectric constant of Bi 0.8 La 0.2 FeO 3 samples occurred due to space charge polarization. However, in Ta-substituted ceramics the stability of dielectric constant with temperature considerably improved. DTA analysis revealed that the peak for ferroelectric transition (T C ) shifted towards higher temperatures for the Tasubstituted BLFO and reached 870 o C for x=0.05.
In the present study, the electrical properties of BiFeO 3 ceramic specimens prepared by solid-state sin-tering method by using two thermal treatment strategies are comparatively investigated. The room temperature XRD pattern shows perovskite single-phase, in the limit of XRD accuracy, for BiFeO 3 ceramic prepared by single-step method. For two-step sintering method sample small amounts of secondary Bi 2 Fe 4 O 9 phases were identified. The ceramics show a non-homogeneous microstructure, consisting of ceramic grains with irregular morphology and interconnected porosity mainly in the grain boundary regions in the case of two-step sintering sample. The most interesting feature is the conduction anomaly observed on the conductivity in the low-frequency range close to dc-conductivity. The Arrhenius plot of the dc-conductivity determined at the lowest frequency vs. 1/T shows two distinct linear regions separated by the mentioned temperature range of (189e244) K, for which the dc conductivity could not be determined from the present impedance spectroscopy data only. It is clear that in the mentioned temperature range (for both samples), a conduction anomaly takes place.
Research Square (Research Square), 2021
0.9Bi 1 − x Nd x FeO 3-0.1PbTiO 3 solid solution where x = 0.05, 0.10, 0.15 and 0.20 were success fully synthesized by the standard solid-state reaction method. The effect of Nd 3+ ion substitution on structural, micro structural, ferroelectric, magnetic, dielectric and magneto-electric properties of 0.9BiFeO 3-0.1PbTiO 3 have been investigated. The XRD analysis for the samples under study revealed distorted rhombohedral structure with R3C space group. 0.9Bi 1 − x Nd x FeO 3-0.1PbTiO 3 where x = 0.05, 0.10, 0.15 and 0.20 i.e. (BNFPT)x compounds crystallised as single-phase materials with the same structure as the parent BiFeO3 compound.. The SEM study revealed the uniform grain scattering for all prepared samples. Raman spectroscopy showed disappearance of some Raman modes indicated a structural phase transition with substitution of Nd dopants at Bi site and also con rmed the distorted rhombohedral perovskite structure of (BNFPT) x compounds with R3c symmetry. Dielectric measurements showed magnetoelectric coupling around Neel temperature in all the samples and also improved dielectric properties with addition of dopants in BiFeO 3 (BFO) compound. All the prepared samples exhibit weak ferro-magnetic character at room temperature. However, the variation in linear behavior and enhancement in magnetization is found at 5 K which shows gradual increase in remnant magnetization from 0.00785 emu/g to 0.37513 emu/g with increase in Nd doping for all (BNFPT) x samples. Nd doping reduces leakage current by three orders of magnitude, from 10 − 4 to 10 − 7. Ferroelectric study revealed the pinning effect in hysteresis loops with low remnant polarization.
Ceramics International, 2015
Eu substituted BiFeO 3 (Bi 1 À x Eu x FeO 3 ; x ¼0-0.15) polycrystalline ceramics were synthesized by a solid state reaction method. Rietveld refinement of X-ray diffraction patterns reveals that samples crystallize in R3c structure for x r0.10 and (R3c þPn2 1 a) phases coexist for x Z 0.12-0.15. The magnetic measurements show weak ferromagnetic nature of Eu substituted BiFeO 3 samples due to ferromagnetic coupling between Eu 3 þ and Fe 3 þ ions. The remnant magnetization is found to increase from 0.0003 emu/g for x ¼ 0.00 to 0.087 emu/g for x ¼ 0.15. The gradual change in line shape of electron spin resonance spectra has been attributed to local distortion induced by Eu substitution. UV-visible absorption spectra in the spectral range 1.12-3.5 eV were dominated by two charge transfer transitions and two doubly degenerate d-d transitions. The optical band gap is found to decrease from 2.25 to 2.16 eV with increasing Eu concentration. Improved dielectric properties with enhancement in frequency independent region of dielectric constant and loss have been observed.
Journal of Alloys and Compounds, 2011
Polycrystalline Bi1−xBaxFe1−yMyO3 (M = Co and Mn; x = 0.1, y = 0.1) were synthesized by solid-state route method to study the compositional driven structural transformations in multiferroics. Room temperature X-ray diffraction patterns confirmed the formation of perovskite structure. Rietveld-refined crystal structure parameters revealed the existence of rhombohedral R3c symmetry for both the samples. The samples were found to be nearly free from any other secondary phases. Raman analysis reveals that Ba atom substitutes Bi site and Mn and Co atom substitutes Fe site into the BiFeO3 with the shifting of phonon modes. The red shift is attributed to Co or Mn doping where as blue shift occurs from Ba doping. The differential scanning calorimetry reveals the corresponding Neel temperature 370 °C and 326 °C for Co and Mn doped samples. Ba and Co substitution with x = 0.1 and y = 0.1 has not affected the Neel temperature of the parent BiFeO3 as well of Ba and Mn substitution. The variation of frequency dispersion in permittivity and loss pattern due to A-site and B-site substitution in BiFeO3 was observed in the dielectric response curve.
Materials Science and Engineering: B, 2011
Polycrystalline (1−x)BiFeO 3-xBaTiO 3 (x = 0.00, 0.10, 0.20 and 0.30) ceramics have been prepared via mixed oxide route. The effect of BaTiO 3 substitution on the dielectric, ferroelectric and magnetic properties of the BiFeO 3 multiferroic perovskite was studied. From XRD analysis it revealed that BaTiO 3 substitution does not affect the crystal structure of the (1−x)BiFeO 3-xBaTiO 3 system up to x = 0.30. Improved dielectric properties were observed in the prepared system. An anomaly in the dielectric constant (ε) was observed in the vicinity of the antiferromagnetic transition temperature. Experimental results suggest that in the (1−x)BiFeO 3-xBaTiO 3 system, the increase of BaTiO 3 concentration leads to the effective suppression of the spiral spin structure of BiFeO 3 , resulting in the appearance of net magnetization. The dependence of dielectric constant and loss tangent on the magnetic field is a evidence of magnetoelectric coupling in (1−x)BiFeO 3-xBaTiO 3 system. The impedance analysis suggests the presence of a temperature dependent electrical relaxation process in the material, which is almost similar for all the concentrations in the present studies. The electrical conductivity has been observed to increase with rise in temperature showing a typical negative temperature coefficient of the resistance (NTCR) behaviors analogous to a semiconductor and suggests a non-Debye type of electrical relaxation.