|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||Q8, Evidence of Ferroelectricity Induced by Epitaxial Strain in Calcium Titanate Thin Films Grown by Molecular-Beam Epitaxy
||Charles M Brooks, Eftihia Vlahos, Michael D Biegalski, Carl-Johan Eklund, Craig J Fennie, Karin M Rabe, Venkatraman Gopalan, Darrell G Schlom
|On-Site Speaker (Planned)
||Charles M Brooks
CaTiO<sub>3</sub> has been predicted by first principles to have strain-induced ferroelectricity. With sufficient tensile strain the development of a polar instability is predicted to occur with polarization along a <110> pseudocubic direction relative to the primitive perovskite lattice vectors. Unlike the strain-induced ferroelectricity observed in SrTiO<sub>3</sub> for both compressive and tensile strains, only tensile strain is predicted to induce ferroelectricity in CaTiO<sub>3</sub> due to large oxygen-octahedron rotations present in the bulk equlibrium phase of CaTiO<sub>3</sub> . In accordance with these predictions, we report evidence of a ferroelectric transition in strained (100) CaTiO<sub>3</sub> films grown by molecular-beam epitaxy (MBE). When deposited on NdGaO<sub>3</sub> and LSAT (LaAlO<sub>3</sub>)<sub>0.3</sub>-(SrAl<sub>1/2</sub>Ta<sub>1/2</sub>O<sub>3</sub>)<sub>0.7</sub> substrates at epitaxially-induced tensile strains of 1.1% and 1.3% respectively, 20 nm thick films of CaTiO<sub>3</sub> exhibit characteristics consistent with ferroelectricity in both second harmonic generation (SHG) and dielectric measurements. At 20 K the CaTiO<sub>3</sub> film on LSAT has a remnant polarization of ~5ÁC/cm<sup>2</sup>. The film appears fully commensurate by x-ray diffraction with a substrate limited rocking curve full-width at half max of 9 arc seconds. Both capacitance vs. temperature and SHG intensity vs. temperature results agree that the paraelectric-to-ferroelectric transition occurs around 150 K. SHG also confirms the prediction of the polarization direction being along the psuedocubic perovskite <110> direction.  C.-J. Eklund, C.J. Fennie, and K.M. Rabe, Phys. Rev. B 79, 220101(R) (2009).