TY - JOUR
T1 - Large tetragonality and room temperature ferroelectricity in compressively strained CaTiO3 thin films
AU - Haislmaier, Ryan C.
AU - Lu, Yanfu
AU - Lapano, Jason
AU - Zhou, Hua
AU - Alem, Nasim
AU - Sinnott, Susan B.
AU - Engel-Herbert, Roman
AU - Gopalan, Venkatraman
N1 - Publisher Copyright:
© 2019 Author(s).
PY - 2019/5/1
Y1 - 2019/5/1
N2 - Ferroelectricity and piezoelectricity are desirable for a variety of higherature applications such as actuators and sensors in heat engines, higherature manufacturing, and space technologies; however, the material candidates are currently limited. Here, we demonstrate that CaTiO3, the prototype perovskite mineral, abundantly found in the Earth, which as a nonpolar material in bulk form, becomes a higherature ferroelectric oxide under compressive strain when grown as a thin film. A strain-phaseerature diagram of CaTiO3 films is created by growing films on various substrates with different in plane strains in order to map out the polar behavior for compressive and tensile strain. Using temperature dependent optical second harmonic generation analysis, we show that tensile strained films exhibit predominantly in-plane polarization with orthorhombiclike point group symmetry with a phase transition below room temperature. On the other hand, compressively strained CaTiO3 films exhibit a near-tetragonal unit cell with a c/a ratio of 1.03, larger than that of classic ferroelectric, e.g., BaTiO3 (c/a ∼1.01). These films exhibit a robust and switchable out-of-plane polarization at room temperature, with a ferroelectric transition temperature up to ∼800 K. Density functional theory calculations reveal that compressive strain gives rise to a large out-of-plane displacement of Ti-cations inside the TiO6 octahedral cages and is the major contributor to the calculated polarization of ∼9 μC/cm2. Given that nearly half of the perovskites exhibit the bulk symmetry of CaTiO3, compressive strain tuning of this perovskite family may prove to be a fertile ground for the discovery of strain-induced piezoelectrics and ferroelectrics at higheratures.
AB - Ferroelectricity and piezoelectricity are desirable for a variety of higherature applications such as actuators and sensors in heat engines, higherature manufacturing, and space technologies; however, the material candidates are currently limited. Here, we demonstrate that CaTiO3, the prototype perovskite mineral, abundantly found in the Earth, which as a nonpolar material in bulk form, becomes a higherature ferroelectric oxide under compressive strain when grown as a thin film. A strain-phaseerature diagram of CaTiO3 films is created by growing films on various substrates with different in plane strains in order to map out the polar behavior for compressive and tensile strain. Using temperature dependent optical second harmonic generation analysis, we show that tensile strained films exhibit predominantly in-plane polarization with orthorhombiclike point group symmetry with a phase transition below room temperature. On the other hand, compressively strained CaTiO3 films exhibit a near-tetragonal unit cell with a c/a ratio of 1.03, larger than that of classic ferroelectric, e.g., BaTiO3 (c/a ∼1.01). These films exhibit a robust and switchable out-of-plane polarization at room temperature, with a ferroelectric transition temperature up to ∼800 K. Density functional theory calculations reveal that compressive strain gives rise to a large out-of-plane displacement of Ti-cations inside the TiO6 octahedral cages and is the major contributor to the calculated polarization of ∼9 μC/cm2. Given that nearly half of the perovskites exhibit the bulk symmetry of CaTiO3, compressive strain tuning of this perovskite family may prove to be a fertile ground for the discovery of strain-induced piezoelectrics and ferroelectrics at higheratures.
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U2 - 10.1063/1.5090798
DO - 10.1063/1.5090798
M3 - Article
AN - SCOPUS:85065795927
SN - 2166-532X
VL - 7
JO - APL Materials
JF - APL Materials
IS - 5
M1 - 051104
ER -