Effect of Nb doping on the morphology and multiferroic behavior of Bi0.9La0.1FeO3 ceramics

Synthesis and study of the crystal structure, microstructure, local ferroelectric, and magnetic properties of the Bi0.9La0.1Fe1−xNbxO3+x (x≤0.02) perovskites have been carried out to shed light on the conditions underlying the appearance of doping-driven instability of the cycloidal antiferromagnetic order in the polar phase of bismuth ferrite. The light aliovalent substitution has not been found to change the rhombohedral symmetry specific to the parent Bi0.9La0.1FeO3. It has been proven that the doping removes the cycloidal modulation characteristic of the rhombohedral phase to stabilize a weak ferromagnetic ferroelectric state. The antiferromagnetic-weak ferromagnetic transition is accompanied by a dramatic decrease in the average size of crystal grains and ferroelectric domains. The magnetic and morphological transformations can be understood by taking into consideration the charge-compensating mechanism involving the formation of lattice defects in the donor-doped materials. The observation of a correlation between the magnetic and morphological evolution in the Bi0.9La0.1Fe1−xNbxO3+x series suggests that structural defects should be considered as an essential factor controlling the magnetic ground state in BiFeO3-based multiferroics.