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Summary: Ab initio study of ferroelectricity in BaTiO3 nanowires
G. Pilania, S. P. Alpay, and R. Ramprasad*
Chemical, Materials, and Biomolecular Engineering, Institute of Materials Science, University of Connecticut,
Storrs, Connecticut 06269, USA
Received 15 January 2009; revised manuscript received 19 May 2009; published 24 July 2009
We present a density-functional theory study of finite-size effects in stoichiometric and nonstoichiometric
BaTiO3 nanowires of varying cross-sectional sizes and sidewall terminations. The tendencies for axial, trans-
verse, and toroidal ferroelectric polarization instabilities in these nanowires have been characterized and pos-
sible driving forces underlying these behaviors have been identified. The critical size for ferroelectricity via
polarization along the nanowire axis is determined to be 12 Å, regardless of the stoichiometry or nanowire
sidewall terminations. The sidewall terminations alter the manner in which axial polarization manifests; for
instance, in nonstoichiometric BaO-terminated nanowires, a "core-shell-type" polarization results beyond the
critical size, while in all other cases, roughly uniform polarization along the same direction was observed
across the entire cross section. A tendency for transverse polarization i.e., normal to the nanowire axis occurs
in nanowires with a cross-sectional size of 16 Å displaying TiO2-terminated sidewall facets. This tendency is
accompanied by a toroidal or vortex polarization state, with the toroidal moment along the nanowire axis, to
mitigate the depolarizing fields due to transverse polarization.
DOI: 10.1103/PhysRevB.80.014113 PACS number s : 77.80. e, 77.22.Ej, 77.84.Dy
I. INTRODUCTION
Owing to their potentially high dielectric constant and
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