Combinatorial discovery of a lead-free morphotropic phase boundary in a thin-film piezoelectric perovskite

Abstract

We report on the discovery of a lead-free morphotropic phase boundary in Sm doped BiFeO 3 with a simple perovskite structure using the combinatorial thin film strategy. The boundary is a rhombohedral to pseudo-orthorhombic structural transition which exhibits a ferroelectric (FE) to antiferroelectric (AFE) transition at approximately Bi 0.86 Sm 0.14 FeO 3 with dielectric constant and out-of-plane piezoelectric coefficient comparable to those of epitaxial (001) oriented Pb(Zr,Ti)O 3 (PZT) thin films at the MPB. The discovered composition may be a strong candidate of a Pb-free piezoelectric replacement of PZT.

Nanoscale Structure and Mechanism for Enhanced Electromechanical Response of Highly Strained BiFeO3 Thin Films

“…[4] Recently, it has been observed that MPB-like features can also exist in appropriately strained, chemically simple materials. [5,6,7] For instance, it has been shown that BiFeO 3 , which possesses a strong electrical polarization (~90-100 μC/cm 2 ) and is a candidate for the replacement of lead-based ferroelectrics, [8,9] can exhibit a strain-induced structural phase transition which gives rise to enhanced electromechanical response. [7] Using epitaxial thin film growth, X-ray reciprocal space mapping (RSM), atomic (AFM) and piezoresponse (PFM) force microscopy we report the nanoscale structural evolution of such strain-induced phase boundaries in BiFeO 3 .…”

Phase coexistence near a morphotropic phase boundary in Sm-doped BiFeO3 films

“…The growth conditions and parameters are detailed elsewhere. 6 Wavelength dispersive x-ray spectroscopy maps over a 100ϫ 100 m 2 area showed homogenous composition within Ϯ1%, and extensive TEM studies using HR-TEM and high angle annular dark field scanning TEM have not revealed macroscale composition inhomogeneity. 7,9 This composition allows us to straddle the MPB as depicted in the temperature-composition phase diagram 10 in Fig.…”

“…6 At this critical doping, the film has features of a morphotropic phase boundary ͑MPB͒ solid solution, consisting of a cell-doubled orthorhombic Pnma phase beyond the MPB and a PbZrO 3 ͑PZO͒-like structural phase in local regions below the MPB. [6][7][8] Electron and laboratory x-ray diffraction studies in Ref. 7 show a superlattice peak at 1/2-order along b in pseudocubic notation that appears to be uniquely associated with the orthorhombic phase.…”

“…[3][4][5][6] Recent comprehensive investigations of Sm-doped BFO ͑BSFO͒ thin films over various compositions discovered a critical composition of 14% Sm-concentration at room temperature. 6 At this critical doping, the film has features of a morphotropic phase boundary ͑MPB͒ solid solution, consisting of a cell-doubled orthorhombic Pnma phase beyond the MPB and a PbZrO 3 ͑PZO͒-like structural phase in local regions below the MPB. [6][7][8] Electron and laboratory x-ray diffraction studies in Ref.…”

Combinatorial thin film composition mapping using three dimensional deposition profiles

“…[1][2][3][4][5] Techniques for the synthesis of combinatorial libraries of materials include solution based methods, 6 advanced manufacturing, and physical vapor deposition. [7][8][9][10][11][12] Among these techniques, combinatorial sputtering provides an opportunity to carefully tune the properties of materials using various parameters such as source voltage, gas pressure, reactive gases, and deposition geometry, making this technique particularly amenable to synthesis of carefully designed, high-quality composition libraries.…”