Dielectric anomalies due to grain boundary conduction in chemically substituted BiFeO3
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We describe systematic studies on Nd and Mn co-doped BiFeO3, i.e., (Bi0.95Nd0.05) (Fe0.97Mn0.03)O3 (BNFM) polycrystalline electroceramics. Raman spectra and X-ray diffraction patterns revealed the formation of rhombohedral crystal structure at room temperature, and ruled out structural changes in BiFeO3 (BFO) after low percentage chemical substitution. Strong dielectric dispersion and a sharp anomaly around 620K observed near the Neel temperature (TN similar to 643K of BFO) support strong magneto-dielectric coupling, verified by the exothermic peak in differential thermal data. Impedance spectroscopy disclosed the appearance of grain boundary contributions in the dielectric data in the region, and their disappearance just near the Neel temperature suggests magnetically active grain boundaries. The resistive grain boundary components of the BNFM are mainly responsible for magneto-dielectric coupling. Capacitive grain boundaries are not observed in the modulus spectra and the dielectric behavior deviates from the ideal Debye-type. The ac conduction studies illustrate short-range order with ionic translations assisted by both large and small polaron hopping. Magnetic studies indicate that the weak antiferromagnetic phase of BNFM ceramics is dominated by a strong paramagnetic response (unsaturated magnetization even at applied magnetic field of 7 T). The bulk BNFM sample shows a good in-plane magnetoelectric coupling (ME) coefficient.
Kumari , S , Ortega , N , Kumar , A , Pavunny , S P , Hubbard , J W , Rinaldi , C , Srinivasan , G , Scott , J F & Katiyar , R S 2015 , ' Dielectric anomalies due to grain boundary conduction in chemically substituted BiFeO 3 ' Journal of Applied Physics , vol 117 , no. 11 , 114102 . DOI: 10.1063/1.4915110
Journal of Applied Physics
© 2015 AIP Publishing LLC. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://dx.doi.org/10.1063/1.4915110
This work was supported by the DOE Grant DE-FG02-08ER46526 and NSF (Fellowship EPS 01002410). N. Ortega acknowledges financial support from the NSF-RII Grant R10701525 and Dr. Ashok Kumar was supported by DOD Grant W911NF-11-1-0204. The authors thank Josue Ortiz Morales (MCC) for his help in the XPS measurements.