Bi deficiency-tuned functionality in multiferroic Bi1-δFe0.95Mn0.05O3 films

Structural evolution and ferroelectric (FE)-to-antiferroelectric (AFE) transition behaviors were observed in Bi1-δFe0.95Mn0.05O3 (100)-textured films with a carefully controlled Bi deficiency concentration δ. Raman spectra revealed an orthorhombic structural transition induced by Mn substitution. The polarization-electric field hysteresis loops and capacitance-voltage loops of Bi1-δFe0.95Mn0.05O3 films clearly demonstrated antiferroelectric behavior with increasing δ. The responses of the domain structure of the Bi1-δFe0.95Mn0.05O3 film under positive and negative applied voltages directly suggested the coexistence of FE and AFE phases. The existence of (100) superstructure reflections and antiparallel displacements of the Bi atoms along the [100] direction observed by transmission electron microscopy unambiguously reveal the AFE phase. The chemical substitution-induced orthorhombic structural transition in BiFe0.95Mn0.05O3 film implies that as the δ concentration increases, the changes in Bi-O bonding and the stereochemical activity of Bi 6s lone pair affect both the ferroelectric distortion and the antiferrodistortive rotation and therefore drive the Bi1-δFe0.95Mn0.05O3 crystal lattice to form a PbZrO3-type orthorhombic phase with an AFE order. A continuing increase in Bi deficiency creates defect dipole complexes which produce an internal field leading to a preferred direction of the ferroelectric domain. The Bi deficiency in multiferroic BiFeO3 provides a new route by which to tune functionality.