Systematic investigation of morphotropic phase boundaries in rare-earth doped BiFeO3

We have investigated structural and ferroelectric properties of BiFeO$_{3}$ doped with rare-earth (RE) elements La, Sm, Gd, Dy, Lu using thin film composition spreads. Previously, we had reported on discovery of a morphotropic phase boundary in (Bi,Sm)FeO$_{3}$.[1] Thin film composition spreads of (Bi,RE)FeO$_{3}$ were fabricated by combinatorial pulsed laser deposition. From scanning xray diffraction, rhombohedral to pseudo-orthorhombic structural transitions are observed. The composition at which the structural transition takes place changes with radii of the RE element: the smaller the ion, the smaller the substitution concentration. This shows that the chemical pressure effect is the cause of the transition. The ferroelectric - antiferroelectric transition is observed for RE doped BiFeO$_{3}$ with smaller radii than the Bi$^{3+}$ ion at the compositions which coincide with the structural transition for each RE dopant. The detailed correlation between the structural properties and ferroelectric and piezoelectric properties will be discussed. This work is supported by DMR, NSF DMR, ARO and the W. M. Keck Foundation.\\[3pt][1] S. Fujino et al., APL 92, 202904 (2008).