Combinatorial discovery of morphotropic phase boundary in a lead-free high $T_{c}$ piezoelectric perovskite Bi$_{1-x}$(RE)$_{x}$FeO$_{3}$

We have recently discovered a morphotropic phase boundary (MPB) in Bi$_{1-x}$Sm$_{x}$FeO$_{3}$ which has a simple perovskite structure. We have systematically investigated compositionally varied Sm doped BiFeO$_{3}$ thin films using the combinatorial approach and found that ferroelectric properties and piezoelectric properties show pronounced enhancement at the MPB. The samples were fabricated by combinatorial pulsed laser deposition on SrTiO$_{3}$ (001) substrates with a SrRuO$_{3}$ buffer layer. The boundary is a rhombohedral to pseudo-orthorhombic structural transition which exhibits a ferroelectric to antiferroelectric transition at approximately Bi$_{0.86}$Sm$_{0.14}$FeO$_{3}$ with intrinsic d$_{33}$ comparable to those of PbZr$_{0.52}$Ti$_{0.48}$O$_{3}$ thin films. Transmission electron microscopy (TEM) reveals presence of nanodomains at the MPB. TEM also reveals onset and formation of antiferroelectric domains as the composition is swept near the MPB, where electron diffraction patterns show systematic structural tilt transitions of the system as a function of Sm doping. Finally, we report on structural transitions and ferroelectric properties in other Bi$_{1-x}$(RE)$_{x}$FeO$_{3}$ systematically studied by the composition spread technique. This work is supported by NSF MRSEC, ARO, and the W. M. Keck Foundation. Research at UNSW is supported by DEST Australia, Australian Research Council Grant DP 0666231 and ARNAM Travel Grant.