Effect of A and B-site substitution with Pb, La and Ti on phase stabilization and multiferroic properties of BiFeO3

The work presents a comparative study of the effects of divalent (Pb), trivalent (La) and tetravalent (Ti) substituents on the multiferroic properties of BiFeO3 (BFO). Both A and B-sites were substituted to obtain the compositions i.e. (Bi1-x-yLaxPby)(Fe1-zTiz)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 Bi0.8La0.2FeO3 compositions exhibited rhombohedral perovskite (R3c) phase, while Bi0.8Pb0.2FeO3 and Bi0.8La0.1Pb0.1FeO3 exhibited cubic phase. Mossbauer 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. High 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 anomaly in the temperature range, 100 degrees C <= T <= 250 degrees C. A systematic reduction in the intensity of the dielectric anomaly peak was observed as a function of Ti concentration which indicates that the anomaly is related to the conductivity and is element specific. However, Mossbauer data revealed absence of Fe2+ state, which ensured that it was not related with the presence of Fe2+ ions. Saturation polarization was found to increase as Ti concentration increased from 0% to 10%. (C) 2015 Elsevier B.V. All rights reserved.