Structure-property relationship of Ba2+ and Ti4+doped multiferroic bismuth ferrite

Abstract

The main focus of this research was to correlate the microstructure with multiferroic properties of Bi1-xBaxFe1-yTiyO3 (x = 0.1, y = 0.0; x = 0.2, y = 0.0; x = 0.3, y = 0.0; and x = 0.3, y = 0.1) samples. The role of doping Ba at Bi-site and Ti at Fe-site on the microstructure and multiferroic properties of BiFeO3 ceramic has been investigated in this research. Single phase Bi1-xBaxFe1-yTiyO3 were synthesized by the conventional solid-state reaction method. The Bi1-xBaxFe1-yTiyO3 dried pellets were calcined at 800oC for 2 hours followed by sintering in the temperature range of 850-900oC. Phase analysis by X–ray diffraction (XRD) confirmed the formation of single phase distorted R3c structure. Increase in unit cell volume with increasing doping concentration has also been reported by XRD analysis. Percentage theoretical density above 95% was achieved for all compositions in this research. Microstructural investigation using the field emission scanning electron microscope (FESEM) showed that, increased doping concentration dramatically reduced the average grain size of Bi1-xBaxFe1-yTiyO3 due to the strong pinning effect of dopants. Ba and Ti doped BFO showed superior values of dielectric constant and ferromagnetic properties. The best values of room temperature dielectric constant (~2885) at 1 kHz frequency was attained by Bi0.7Ba0.3Fe0.9Ti0.1O3 samples having average grain size in the range of 1.0-1.05 μm. The lack of oxygen vacancies in this sample provided high resistivity and thereby resulted in high dielectric constant. At higher temperatures a considerable increase in the dielectric constant of Bi0.9Ba0.1FeO3 and Bi0.7Ba0.3FeO3 samples occurred due to space charge polarization. However, in Bi0.8Ba0.2FeO3 and Bi0.7Ba0.3Fe0.9Ti0.1O3 the stability of dielectric constant with temperature was considerably improved due to lack of oxygen vacancy in these samples. Moreover, DTA analysis revealed the shift of peak for ferroelectric transition (TC) towards higher temperatures with increased doping concentration, which reached 866oC for Bi0.7Ba0.3Fe0.9Ti0.1O3. As expected from the XRD results the remnant magnetization also increased with doping concentration and reached 0.9 emu/gram for Bi0.7Ba0.3Fe0.9Ti0.1O3. This increase in remnant magnetization can be attributed to the increased distortion with increasing doping concentration. Maximum coercivity (~2.5kOe) was attained by single Ba doped Bi1-xBaxFe1-yTiyO3 (x = 0.1, y = 0.0; x = 0.2, y = 0.0; x = 0.3, y = 0.0) samples. However the decrease in coercivity to 1.8kOe in Bi0.7Ba0.3Fe0.9Ti0.1O3 sample can be attributed to the easiness of spin flipping in this sample due to substitution of Fe-site with Ti having different valance.