Emergent room temperature polar phase in CaTiO3 nanoparticles and single crystals
Mariola O. Ramirez,
Tom T. A. Lummen,
Irene Carrasco,
Eftihia Barnes,
Ulrich Aschauer,
Dagmara Stefanska,
Arnab Sen Gupta,
Carmen de las Heras,
Hirofumi Akamatsu,
Martin Holt,
Pablo Molina,
Andrew Barnes,
Ryan C. Haislmaier,
Przemyslaw J. Deren,
Carlos Prieto,
Luisa E. Bausá,
Nicola A. Spaldin,
Venkatraman Gopalan
Affiliations
Mariola O. Ramirez
Departamento Física de Materiales, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid 28049, Spain
Tom T. A. Lummen
Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Irene Carrasco
Advanced Technology Institute, Department of Electrical and Electronic Engineering, University of Surrey, Guildford GU2 7XH, United Kingdom
Eftihia Barnes
Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Ulrich Aschauer
Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland
Dagmara Stefanska
Institute of Low Temperature and Structure Research, Polish Academy of Science, Wroclaw, Poland
Arnab Sen Gupta
Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Carmen de las Heras
Departamento Física de Materiales, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid 28049, Spain
Hirofumi Akamatsu
Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Martin Holt
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA
Pablo Molina
Departamento Física de Materiales, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid 28049, Spain
Andrew Barnes
Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Ryan C. Haislmaier
Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Przemyslaw J. Deren
Institute of Low Temperature and Structure Research, Polish Academy of Science, Wroclaw, Poland
Carlos Prieto
Instituto de Ciencia de Materiales de Madrid, ICMM, (CSIC), C/Sor Juana Inés de la Cruz 3, Madrid 28049, Spain
Luisa E. Bausá
Departamento Física de Materiales, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid 28049, Spain
Nicola A. Spaldin
Materials Theory, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
Venkatraman Gopalan
Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Polar instabilities are well known to be suppressed on scaling materials down to the nanoscale, when the electrostatic energy increase at surfaces exceeds lowering of the bulk polarization energy. Surprisingly, here we report an emergent low symmetry polar phase arising in nanoscale powders of CaTiO3, the original mineral named perovskite discovered in 1839 and considered nominally nonpolar at any finite temperature in the bulk. Using nonlinear optics and spectroscopy, X-ray diffraction, and microscopy studies, we discover a well-defined polar to non-polar transition at a TC = 350 K in these powders. The same polar phase is also seen as a surface layer in bulk CaTiO3 single crystals, forming striking domains with in-plane polarization orientations. Density functional theory reveals that oxygen octahedral distortions in the surface layer lead to the stabilization of the observed monoclinic polar phase. These results reveal new ways of overcoming the scaling limits to polarization in perovskites.
