Ferroelectric Phase Transition in Individual Single-Crystalline BaTiO₃ Nanowires

Abstract

We report scanned probe characterizations of the ferroelectric phase transition in individual barium titanate (BaTiO3) nanowires. Variable-temperature electrostatic force microscopy is used to manipulate, image, and evaluate the diameter-dependent stability of ferroelectric polarizations. These measurements show that the ferroelectric phase transition temperature (TC) is depressed as the nanowire diameter (dnw) decreases, following a 1/dnw scaling. The diameter at which TC falls below room temperature is determined to be approximately 3 nm, and extrapolation of the data indicates that nanowires with dnw as small as 0.8 nm can support ferroelectricity at lower temperatures. We also present density functional theory (DFT) calculations of bare and molecule-covered BaTiO3 surfaces. These calculations indicate that ferroelectricity in nanowires is stabilized by molecular adsorbates such as OH and carboxylates. These adsorbates are found to passivate polarization charge more effectively than metallic electrodes, explaining the observed stability of ferroelectricity in small-diameter BaTiO3 nanowires.

Ferroelectrics at the nanoscale

“…In a noteworthy study by Spanier et al [18], the influence of the depolarising field on the stability of written domains in BaTiO 3 nanowires was investigated. Domains were written perpendicular to the axis of a series of nanowires, by applying a voltage through a scanning probe microscopy tip, as has been done in previous nanoscale polarisation studies [19][20][21].…”

“…Another interpretation of the data obtained by Spanier et al might be that the drive for polar reorientation to lie parallel to the nanowire axis dominates behaviour in smaller diameter nanowires. In the as-grown state, the lack of EFM Figure 3 (online colour at: www.pss-a.com) Curie temperature inferred from loss of electric field microscopy contrast from 'bits' written into BaTiO 3 nanowires, such that their polarisation was perpendicular to the nanowire axis [18]. Inset shows that the extent to which T C is suppressed varies linearly with the inverse of the nanowire diameter (i.e.…”

“…This is primarily due to the ability of the ferroelectric to minimize or eliminate depolarising fields by either the formation of 180° domains [15,16], reorientation of polarisation [17,22,25] or the influence of compensating charges readily available under atmospheric conditions [18,29].…”

Ultrafast Photovoltaic Response in Ferroelectric Nanolayers

“…This period is determined by a trade-off between the energy of the uncompensated depolarization field and the domain walls [8]. At higher temperatures, the volatile adsorbate species that stabilize the monodomain phase [1,5] are removed. The periodicity of the stripe domains gives rise to in-plane satellites, displaced by ∆Q r = 2π/Λ, which appear as a ring of Page 5 of 17 diffuse scattering around the Bragg peak.…”

X-ray photoelectron diffraction study of relaxation and rumpling of ferroelectric domains in BaTiO3(001)

“…The second step was then to optimize the values of N + , N − , and N in , the proportions of each ferroelectric domain type. Here, we present the results of method (2). First, the linear combination of N + , N − , and N in is found using the bulk atomic structure in the ferroelectric phase.…”