Metastable perovskite phases - multiferroics in the BiFeO3 - BiScO3 - LaFeO3 - LaScO3 system
Department of Materials and Ceramic Engineering, University of Aveiro. Portugal
Perovskite bismuth ferrite is one of the most studied multiferroics since this compound can be obtained using the conventional preparation methods. BiFeO3 is ferroelectric until TС=1083 K, while the antiferromagnetic phase transition occurs at TN=643 K. The temperatures of both transitions are too high and far from each other which makes difficult a beneficial use of the lattice-magnetic coupling effect.
Recently, we initiated a systematic study of the quasi-quadruple BiFeO3–BiScO3–LaFeO3–LaScO3 perovskite system. Three end members of this system, BiFeO3, LaFeO3 and LaScO3, can be obtained using the conventional methods, while a bulk perovskite BiScO3 phase can be synthesized under the high-pressure conditions only. One of the ideas of exploration of the Bi1-xLaxFe1-yScyO3 system is to control the temperatures of the magnetic and the polar transitions. In this system, all the constituent cations are trivalent that makes possible to vary the parameters x and y independently. Hence, one can decrease the temperature of polar transition by means of a replacement of bismuth by lanthanum and decrease the temperature of magnetic transition through an iron-to-scandium substitution. Such substitutions were found to result in formation of new structural phases in both the as-prepared and the annealed compositions with unique combinations of polar, magnetic and elastic order parameters.