Evidence of improved ferroelectric phase stabilization in Nd and Sc co-substituted BiFeO3 (original) (raw)
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Enhancement of magnetic and electrical properties in Sc substituted BiFeO3 multiferroic
Physica B: Condensed Matter, 2014
Polycrystalline BiFe 1 À x Sc x O 3 (x ¼ 0, 0.05, 0.1 and 0.15) compounds are prepared using solid state reaction. The XRD patterns show that all compounds are crystallized in rhombohedral structure with R3c space group. An induced weak ferromagnetism in Sc substituted BiFeO 3 due to suppression of spiral modulated spin structure is revealed. In addition, a spin glass like behaviour is observed from the zero field cooled (ZFC) and field cooled (FC) magnetization curves in the low temperature region. Further, the coupling between the ferroelectric and (anti) ferromagnetic orders is evident from the appearance of anomaly in the dielectric data near the magnetic Néel temperature (373 1C). The reduction of oxygen vacancies due to Sc substitution is evident from the ac conductivity data and the suppressed anomaly in dielectric data at 220 1C. The temperature dependence of ac conductivity is consistent with correlated barrier hopping (CBH) model. The temperature dependent ac conductivity and activation energies indicate that electronic conduction, oxygen vacancies movement and creation of defects are the prime contributors to the ac conductivity in measured temperature regions. The improved magnetic and electrical properties due to the structural modification are prominent for novel device applications.
Journal of Alloys and Compounds, 2015
The work presents a comparative study of the effects of divalent (Pb), trivalent (La) and tetravalent (Ti) substituents on the multiferroic properties of BiFeO 3. Both A and B-sites were substituted to obtain the compositions i.e. (Bi 1-x-y La x Pb y)(Fe 1-z Ti z)O 3 (x, y = 0, 0.1, 0.2 and z = 0, 0.05, 0.1, 0.15). Each of the substituent was particularly chosen i.e. Pb was chosen to keep the lone pair character which is the similar case as Bi ion. Additionally isovalent La was chosen to achieve single phase by reducing Bi volatization. Both these ions, on substitution, stabilized the crystal structure and suppressed the formation of extra phases which are unavoidable in pure BFO. All the Ti substituted and Bi 0.8 La 0.2 FeO 3 compositions exhibited rhombohedral perovskite (R3c) phase, while Bi 0.8 Pb 0.2 FeO 3 and Bi 0.8 La 0.1 Pb 0.1 FeO 3 exhibited cubic phase. Mössbauer measurements revealed that impurity phase in case of compositions with divalent and trivalent substituents, disappeared completely when Ti substituted Fe. For all the compositions Fe ions were found in +3 state. Higher temperature dielectric properties showed that all the compositions were ferroelectric with paraelectric transition lying well above the room temperature. Weak ferromagnetism was found in Ti substituted compositions where coercivity was found to increase as the Ti concentration increases. All the BFO samples substituted with Pb, exhibited a dielectric Highlights A-site substitution: to stabilize phase, and retain lone pair character. For all the compositions, +3 oxidation state of Fe ions was achieved. Anomalous dielectric anomaly was progressively suppressed with Ti substitution. An increase in coercivity has been achieved with increase in Ti concentration. Polarization and magnetization has been found to increase with Ti concentration.
Crystal structure and multiferroic properties of Gd-substituted BiFeO3
Applied Physics Letters, 2008
Room-temperature crystal structure, local ferroelectric, and magnetic properties of the Bi 1−x Gd x FeO 3 ͑x = 0.1, 0.2, 0.3͒ polycrystalline samples have been investigated by x-ray diffraction, piezoresponse force microscopy, and magnetometry techniques. Performed measurements have revealed a sequence of the composition-driven structural phase transitions R3c → Pn2 1 a ͑occurs at x ϳ 0.1͒ and Pn2 1 a → Pnma ͑takes place within the concentrational range of 0.2Ͻ x Ͻ 0.3͒. The latter structural transformation is attributed to the substitution-induced suppression of the polar displacements. Gd substitution has been shown to effectively induce the appearance of the spontaneous magnetization, thus indicating a promising way for improving multiferroic properties of antiferromagnetic BiFeO 3 .
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.
Crystal structure refinement, dielectric and magnetic properties of Sm modified BiFeO3 multiferroic
Journal of Molecular Structure, 2015
SrFe 12 O 19 (SFO), Sr 0.5 Ca 0.5 Fe 12 O 19 (SCFO) and Sr 0.5 Pb 0.5 Fe 12 O 19 (SPFO) hexaferrites have been synthesized by a conventional solid state reaction technique. Powder X-ray diffraction and Rietveld refinement confirm the presence of M-type hexagonal phase in prepared samples. However in SCFO, secondary phase was also present with main phase. Analysis of Nyquist's plots of SFO hexaferrite revealed the contribution of many electrically active regions corresponding to bulk mechanism, distribution of grain boundaries and electrode processes also. Both conductivity and electric modulus formalisms have been employed to study the relaxation dynamics of charge carriers. A perfect overlapping of the normalized plots of modulus isotherms on a single 'super curve' for all the studied temperatures reveals a temperature independence of dynamic processes involved in conduction and for relaxation. In SPFO sample coercivity is reduced effectively but accompanied with increase in magnetization, which is requirement for hexaferrites to be used as magnetic recording media.
2013
Here we studied the effect of homovalent Pr 3+ and Y 3+ substitution on the crystal structure, dielectric, electronic polarization and magnetic properties of the BiFeO 3 multiferroic ceramic. The samples were synthesized by the conventional solid-state reaction method. Pure phase formation of Pr doped BiFeO 3 (BFO) has been obtained, while Y 3+ doped BFO has shown a few impurity peaks. It has shown that the crystal structure of the compounds is described within the space group R3c. Pr 3+ modified BFO has shown an anomaly in the ε r vs. T plot around and a Néel temperature 'T N ' ∼ 370 • C. P -E hysteresis loops have shown higher value of remnant polarization for Pr 3+ modified BFO. Magnetic properties of ceramics are determined by the ionic radius of the substituting element. Experimental results propose that the increase in the radius of A-site ion leads to effective suppression of the spiral spin structure of BiFeO 3 , resulting in the appearance of net magnetization.
Ferroelectrics, 2018
Multiferroic materials with magnetoelectric properties, due to their coupling between the electrical and magnetic properties have attracted the attention of many researchers. Perovskite structured materials based on BiFeO 3 are a class of materials largely considered in these studies. In this work, Bi 1-x Nd x Fe 0.99 Co 0.01 O 3 (x ¼ 0.05, 0.10 and 0.20) compositions were synthesized aiming a better understanding of the crystal and electronic structure role in ferroic properties of these materials. Structural studies were made by X-ray diffraction and Rietveld refinement; evidencing the rhombohedral symmetry of the samples with space group R3c. Electron density calculations were performed by the maximum entropy method. These studies showed that Nd 3þ substitution causes distortions in the unit cell, which have influence on the magnetic properties. Also, the electron density maps showed the bonds between the iron and oxygen ions did not changed a lot. But the Minimum Electron Density observations were enough to conclude that the ferroelectric and the dielectric properties of Bi 1-x Nd x Fe 0.99 Co 0.01 O 3 compositions would be modified with the Nd 3þ substitution.
Enhanced magnetization and improved insulating character in Eu substituted BiFeO3
Journal of Applied Physics, 2014
The polycrystalline Bi 1Àx Eu x FeO 3 (x ¼ 0, 0.05, and 0.1) ceramics were synthesized by conventional solid-state route. X-ray diffraction studies and Raman measurements revealed that the compounds crystallized in rhombohedral structure with R3c space group. In addition, a nominal percentage of orthorhombic phase was observed in 10 mol. % Eu substituted BiFeO 3 . Appearance of weak ferromagnetism and significant increase in N eel temperature T N in the substituted compounds were discussed on the basis of structural distortions. Enhanced remnant magnetization of 75 memu/g and large coercive field of 6.4 k € Oe were observed in 10 mol. % Eu substituted BiFeO 3 . Equivalent circuit model was employed to estimate the grain and grain boundary contributions towards the electrical parameters such as resistance and conductivity. Non-Debye type of relaxation was confirmed from impedance and electric modulus studies. The obtained frequency variation of ac conductivity at different temperature obeys Jonscher's power law and is consistent with the correlated barrier hopping model. Temperature variations of ac conductivity explained that electronic hopping, oxygen vacancies movement, and/or creation of defects contribute to conduction in all the compounds. V C 2014 AIP Publishing LLC. [http://dx.