Stabilization of highly polar BiFeO 3 like structure: a new interface design route for enhanced ferroelectricity in artificial perovskite superlattice

Stabilization of highly polar BiFeO 3 like structure: a new interface design route for enhanced ferroelectricity in artificial perovskite superlattice Speaker: Xifan Wu Temple University

Outline Part I. Introduction Ø Ferroelectricity (FE) and Octahedron rotations in perovskites Part II. Puzzling FE properties in BaTiO 3 /CaTiO 3 superlattice Ø Unexpected large FE and piezoelectricity Ø Interface reconstruction Part III. Stabilized BFO-like structure at interfaces of BTO/CTO Ø Model Hamiltonian fitted by DFT Part IV. Prediction of new FE materials based on the concept learned Ø Generating FE superlattice from nonpolar perovskites only Part V. Conclusion: Comparison among interface design approaches

Introduction: Octahedron rotations and FE in perovskites Perovskites only dominated by FE distortion: BaTiO 3, PbTiO 3, Ø Strong FE instability, polarization ~ 27 µc/cm 2 Ø Only FE structural distortion develops at room temperature Ø Without any oxygen octahedron rotations Г 4 (slater) FE mode

Introduction: Octahedron rotations and FE in perovskites Perovskites: oxygen octahedron rotations and tilts: more common CaTiO 3 (CTO)-like CTO of Pbnm In phase Rotation (a 0 a 0 c + ) Tilts (a - a - c 0 )

Introduction: Octahedron rotations and FE in perovskites Perovskites: oxygen octahedron rotations and tilts: more common CaTiO 3 (CTO)-like CTO of Pbnm Oxygen rotation suppress FE D. Vanderbilt and W. Zhong, Ferroelectrics 206, 181 (1997). N. A. Benedek and C. Fennie, J. Phys. Chem. C 117, 13339 (2013) In phase Rotation (a 0 a 0 c + ) Tilts (a - a - c 0 ) Suppressed FE Favored antipolar

Introduction: Octahedron rotations and FE in perovskites Perovskites: oxygen octahedron rotations and tilts: more common BiFeO 3 (BFO)-like BFO of R3C Out of phase Rotation (a 0 a 0 a - ) Strongly favored FE Ø Curie temperature ~ 1100 K Ø Neel temperature ~ 643 K Ø Polarization ~ 90 μc/ cm 2 Tilts (a - a - a 0 )

Introduction: Octahedron rotations and FE in perovskites CTO-like BFO-like Widespread! Relative rare! In phase Rotation (a 0 a 0 c + ) Out of phase Rotation (a 0 a 0 c - ) Tilts (a - a - c 0 ) Tilts (a - a - c 0 )

Puzzling FE in BaTiO3/CaTiO3 superlattices Polariza6on measurement S. S. A. Seo and H. N. Lee, Appl. Phys. LeE. 94, 232904 (2009). S. S. A. Seo et al Advanced Material (2007). Piezoelectricity measurement J. Y. Jo, et al, Phys. Rev. Lett. 104, 207601 (2010) Large Ferroelectricity and related properties: Ø d 33 = 54 pm/v in 2BaTiO 3 /4CaTiO 3 Ø Large polarization in nbatio 3 /ncatio 3 (n is small) STO substrate

Puzzling FE in BaTiO3/CaTiO3 superlattices DFT calculation: modeling of the structures FE distortion Octahedron Rotation a 0 a 0 c - Octahedron tilts a - a - c 0 Wang et al, Phys. Rev. X., 6, 011027 (2016)

Puzzling FE in BaTiO3/CaTiO3 superlattices DFT calculation: modeling of the structures DFT predictions are consistent with experiments d 33 (2BTO4CTO)/ d 33 (BTO ;ilm) ~ 0.98 (theory) ~ 1.0 (experiment)!!

Puzzling FE in BaTiO 3 /CaTiO 3 superlattices What we expect based on bulk properties of BTO and CTO dielectric slab model 1. J. B. Neaton and K. M. Rabe, Appl. Phys. LeE. 82, 1586-1588 (2003). p 3 (D) p 2 (D) A 1 TiO 3 A 2 TiO 3 p 1 (D) p 0 (D) p 1 (D) A 3 TiO 3 p 2 (D) P D p 3 (D)

Puzzling FE in BaTiO 3 /CaTiO 3 superlattices What we expect based on bulk properties of BTO and CTO dielectric slab model 1. J. B. Neaton and K. M. Rabe,Appl. Phys. LeE. 82, 1586-1588 (2003). p 3 (D) p 2 (D) A 1 TiO 3 p 1 (D) A 2 TiO 3 p 0 (D) p 1 (D) A 3 TiO 3 P D p 2 (D) p 3 (D) Interface effect can not be neglected!!

Puzzling FE properties in BaTiO 3 /CaTiO 3 superlattice: Interface effect In-phase rotation Out-of-phase rotation In-plane P Out-of-plane P Antipolar mode Tilts Large Zero Strain induced in-plane P 6 BTO/6CTO on STO substrate Wang et al, Phys. Rev. X., 6, 011027 (2016) Large anti polar distortion Large Dominated by strained bulk CaTiO3

Puzzling FE properties in BaTiO 3 /CaTiO 3 superlattice: Interface effect In-phase rotation Out-of-phase rotation In-plane P Out-of-plane P Antipolar mode Tilts Zero Zero Zero Zero Zero 6 BTO/6CTO on STO substrate Dominated by strained bulk BaTiO 3 Wang et al, Phys. Rev. X., 6, 011027 (2016)

Outline In-phase rotation Out-of-phase rotation In-plane P Out-of-plane P Antipolar mode Tilts Dielectric slab model 6 BTO/6CTO on STO substrate Wang et al, Phys. Rev. X., 6, 011027 (2016)

Puzzling FE properties in BaTiO 3 /CaTiO 3 superlattice: Interface effect In-phase rotation Out-of-phase rotation In-plane P Out-of-plane P Antipolar mode Tilts 6 BTO/6CTO on STO substrate Wang et al, to be published in Phys. Rev. X.

Puzzling FE properties in BaTiO 3 /CaTiO 3 superlattice: Interface effect In-phase rotation Out-of-phase rotation In-plane P Out-of-plane P Antipolar mode Tilts suppressed Induced Induced Enhanced P suppressed suppressed 6 BTO/6CTO on STO substrate Wang et al, Phys. Rev. X., 6, 011027 (2016)

Octahedron rotations in perovskites high-resolution (amplitude contrast) transmission electron microscopy Simulated TEM based on DFT theory By Jianguo Wen and Dean Miller, Argonne Viewed from [110] direction Wang et al, to be published in Phys. Rev. X.

Model Hamiltonian fitted by DFT Model Hamiltonian CTO-like CTO on SrTiO3 substrate In phase Rotation (a 0 a 0 c + ) Tilts (a - a - c 0 ) R z i :in phase rotation N. A. Benedek and C. Fennie, Why are there so few perovskite ferroelectrics, J. Phys. Chem. C 117, 13339 (2013). R z o :out of phase rotation R xy :OOR tilt AFE xy :in plane antipolar FE xy :in plane FE FE z :out of plane FE Wang et al, Phys. Rev. X., 6, 011027 (2016)

Model Hamiltonian fitted by DFT Model Hamiltonian BFO-like CTO on SrTiO3 substrate Out of phase Rotation (a 0 a 0 c - ) Tilts (a - a - c 0 ) R z i :in phase rotation J.L. Blok, K.M. Rabe, D. Vanderbilt, D.H.A. Blank, and G. Rijnders, Phys. Rev. B 84, 205413 (2011). R z o :out of phase rotatio R xy :OOR tilt AFE xy :in plane antipolar FE xy :in plane FE FE z :out of plane FE Wang et al, to be published in Phys. Rev. X.

Model Hamiltonian fitted by DFT Ground state strained CaTiO 3 : CTO-like Metastable strained CaTiO 3 : BFO-like Assuming the oxygen octahedron rota6on and 6lt are tunable parameters Wang et al, Phys. Rev. X., 6, 011027 (2016)

Model Hamiltonian fitted by DFT Phase stabilities of ground state CTO CTO-like phase and metastable CTO BFO-like Natural ground state E>0 CTO- like stable E<0 BFO- like stable Tilts Rota6on Wang et al, Phys. Rev. X., 6, 011027 (2016)

Model Hamiltonian fitted by DFT In-phase rotation Out-of-phase rotation In-plane P Out-of-plane P Antipolar mode Tilts Stabilized BFO-like phase 1. Moderately suppressed tilting and rotation 2. Electric and mechanical boundary conditions Wang et al, Phys. Rev. X., 6, 011027 (2016)

Interface approach: Generating FE from nonpolar perovskites only A BO3 Out of phase rotation tilt In phase rotation cubic-like non polar perovskite Xifan Wu - - EFRC annual review Wang et al, Phys. Rev. X., 6, 011027 (2016)

Interface approach: Generating FE from nonpolar perovskites only A BO3 A BO3 Out of phase rotation tilt In phase rotation cubic-like non polar perovskite CTO-like non polar perovskite Xifan Wu - - EFRC annual review Wang et al, Phys. Rev. X., 6, 011027 (2016)

Interface approach: Generating FE from nonpolar perovskites only A BO3 A BO3 Out of phase rotation tilt 1A BO3/1A BO3 In phase rotation cubic-like non polar perovskite CTO-like non polar perovskite Xifan Wu - - EFRC annual review Wang et al, Phys. Rev. X., 6, 011027 (2016) BFO-like polar phase

Acknowledgement Ø Hongwei Wang (postdoc of Temple Physics) Ø Jianguo Wen (TEM, Argonne) Ø Dean Miller (TEM, Argonne) Ø Qibin Zhou (Rutgers Physics) Ø Karin M. Rabe (Rutgers Physics) Ø Mohan Chen (Princeton, Engineering) Ø Ho-Nyung Lee (Thin-film, Oak Ridge)