Influence of Transition Metal Ion Doping on Structural and Dielectric Properties of Sol-gel Synthesized Bismuth Ferrite Nanoceramics

Bismuth layered ferroelectric materials are promising candidates for sensors, actuators and nonvolatile random access memory devices. In addition to these potential candidates, a rhombohedrally distorted perovskite structured bismuth ferrite (BFO) material with space group R3c has also been well recognized owing to the coexistence of ferroelectric and antiferromagnetic properties which are advantageous in high density FeRAM devices. The main recede of the BFO material is low electrical resistivity attributed to the valence fluctuations of Fe ions (Fe3+ to Fe2+) that hampers the magnitude of remnant magnetization at 300K. In order to enhance the physical properties and also to prevent impurity phases during the processing of bismuth ferrite compound, chemical substitution of transition metal ion (Mn) on to Fe site in the crystal lattice of BFO is very essential in order to suit this material especially for memory devices. In the present work, a series of BiMn x Fe 1-x O 3 (x = 0, 0.03, 0.05 and 0.10) ceramics were synthesized via low temperature sol-gel route and subsequently the structural, microstructural, optical and dielectric properties were carried out on these samples by using X-ray diffractometer (XRD), scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR) and LCR meter respectively. The Bragg peaks in the XRD patterns confirmed the monophasic perovskite BFO structure in all the compositions and merging of (104) and (110) peaks indicate the structural modification which could be attributed to the ionic radii difference of Mn and Fe. The SEM micrographs revealed the existence of nanosized granular shaped grains with negligible porosity and also there is a gradual reduction in the granular size with increase in Mn-doping concentration. The FTIR spectral analysis of these nanoceramic samples showed the strong absorption bands in the wavenumber range of 450-600cm−1 which corroborated the perovskite structure of BFO material. Interestingly, the dielectric constant measured in the frequency range of 20Hz – 1MHz at 300K is higher for Mn doped ceramics than undoped BFO samples. A low frequency dielectric dispersion is evident in the frequency dependence plot of the dielectric constant of these samples.