LuGaO3: A Polar Hexagonal Perovskite

Abstract

Designing functional materials is a promising route to enhance modern technologies. Here, an unreported hexagonal perovskite, LuGaO₃, is successfully synthesized in thin-film form, and its structure is characterized and compared to isostructural LuFeO₃, along with solid solutions of the two (LuFe_xGa_1–xO₃, for x = 0.25–0.75). The addition of gallium was found to degrade the structural quality of LuFeO₃, rendering the hexagonal phase nearly unobservable in pure LuGaO₃. Extensive growth experiments (and thermodynamic phase diagrams for related systems) suggest a tendency for LuGaO₃ to decompose into Lu₂O₃ and Lu₃Ga₅O₁₂. In turn, unconventionally high synthesis pressures (500–2000 mTorr) during pulsed-laser deposition are required to stabilize the hexagonal phase. While device-based measurements demonstrate an obvious ferroelectric hysteresis for LuFeO₃, the addition of gallium (seemingly) quenches any observable ferroelectric polarization while also lowering the leakage and dielectric constant. Second-harmonic-generation measurements and piezoresponse force microscopy, however, indicate that LuGaO₃ is polar and can be switched under an electric field. This discrepancy with device-based measurements warrants further study, upon improving the structural quality, before ferroelectricity can be claimed unequivocally. These findings demonstrate that designer materials can be synthesized, but further refinement to predictive approaches is needed to bring them more in-line with experimental reality.