Oak Ridge, TN, United States
Oak Ridge, TN, United States

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Balke N.,Center for Nanophase Materials science | Balke N.,Institute for Functional Imaging of Materials | Maksymovych P.,Center for Nanophase Materials science | Maksymovych P.,Institute for Functional Imaging of Materials | And 11 more authors.
ACS Nano | Year: 2015

Ferroelectricity in functional materials remains one of the most fascinating areas of modern science in the past several decades. In the last several years, the rapid development of piezoresponse force microscopy (PFM) and spectroscopy revealed the presence of electromechanical hysteresis loops and bias-induced remnant polar states in a broad variety of materials including many inorganic oxides, polymers, and biosystems. In many cases, this behavior was interpreted as the ample evidence for ferroelectric nature of the system. Here, we systematically analyze PFM responses on ferroelectric and nonferroelectric materials and demonstrate that mechanisms unrelated to ferroelectricity can induce ferroelectric-like characteristics through charge injection and electrostatic forces on the tip. We will focus on similarities and differences in various PFM measurement characteristics to provide an experimental guideline to differentiate between ferroelectric material properties and charge injection. In the end, we apply the developed measurement protocols to an unknown ferroelectric material. © 2015 American Chemical Society.

Boreyko J.B.,Center for Nanophase Materials science | Mruetusatorn P.,University of Tennessee at Knoxville | Sarles S.A.,University of Tennessee at Knoxville | Retterer S.T.,Center for Nanophase Materials science | And 2 more authors.
Journal of the American Chemical Society | Year: 2013

Droplet interface bilayers (DIBs) are a robust platform for studying synthetic cellular membranes; however, to date no DIBs have been produced at cellular length scales. Here, we create microscale droplet interface bilayers (μDIBs) at the interface between aqueous femtoliter-volume droplets within an oil-filled microfluidic channel. The uniquely large area-to-volume ratio of the droplets results in strong evaporation effects, causing the system to transition through three distinct regimes. First, the two adjacent droplets shrink into the shape of a single spherical droplet, where an augmented lipid bilayer partitions two hemispherical volumes. In the second regime, the combined effects of the shrinking monolayers and growing bilayer force the confined bilayer to buckle to conserve its mass. Finally, at a critical bending moment, the buckling bilayer fissions a vesicle to regulate its shape and mass. The μDIBs produced here enable evaporation-induced bilayer dynamics reminiscent of endo-and exocytosis in cells. © 2013 American Chemical Society.

Sahu G.,Center for Nanophase Materials science | Rangasamy E.,Center for Nanophase Materials science | Li J.,Oak Ridge National Laboratory | Chen Y.,Oak Ridge National Laboratory | And 3 more authors.
Journal of Materials Chemistry A | Year: 2014

Lithium-ion conducting solid electrolytes show potential to enable high-energy-density secondary batteries and offer distinctive safety features as an advantage over traditional liquid electrolytes. Achieving the combination of high ionic conductivity, low activation energy, and outstanding electrochemical stability in crystalline solid electrolytes is a challenge for the synthesis of novel solid electrolytes. Herein we report an exceptionally low activation energy (Ea) and high room temperature superionic conductivity via facile aliovalent substitution of Li3AsS4 by Ge, which increased the conductivity by two orders of magnitude as compared with the parent compound. The composition Li3.334Ge0.334As 0.666S4 has a high ionic conductivity of 1.12 mS cm -1 at 27 °C. Local Li+ hopping in this material is accompanied by a distinctive low activation energy Ea of 0.17 eV, being the lowest of Li+ solid conductors. Furthermore, this study demonstrates the efficacy of surface passivation of solid electrolyte to achieve compatibility with metallic lithium electrodes. © 2014 the Partner Organisations.

Wang Y.,Griffith University | Sumpter B.G.,Center for Nanophase Materials science | Huang J.,Center for Nanophase Materials science | Zhang H.,Griffith University | And 4 more authors.
Journal of Physical Chemistry C | Year: 2015

Organic/inorganic hybrid perovskite materials are highly attractive for dye-sensitized solar cells as demonstrated by their rapid advances in energy conversion efficiency. In this work, the structures, energetics, and electronic properties for a range of stoichiometric surfaces of the orthorhombic perovskite CH3NH3PbI3 are theoretically studied using density functional theory. Various possible spatially and constitutionally isomeric surfaces are considered by diversifying the spatial orientations and connectivities of surface Pb-I bonds. The comparison of surface energies for the most stable configurations identified for all surfaces shows that the stabilities of stoichiometric surfaces are mainly dictated by the coordination numbers of surface atoms, which are directly correlated with the number of broken bonds. Additionally, Coulombic interactions between I anions and organic countercations on the surface also contribute to the stabilization. Electronic properties are compared between the most stable (100) surface and the bulk phase, showing generally similar features except for the lifted band degeneracy and the enhanced bandgap energy for the surface. These studies on the stoichiometric surfaces serve as a first step toward gaining a fundamental understanding of the interfacial properties in the current structural design of perovskite based solar cells, in order to help facilitate further breakthroughs in solar conversion efficiencies. (Figure Presented). © 2014 American Chemical Society.

Rangasamy E.,Center for Nanophase Materials science | Li J.,Oak Ridge National Laboratory | Sahu G.,Center for Nanophase Materials science | Dudney N.,Oak Ridge National Laboratory | Liang C.,Center for Nanophase Materials science
Journal of the American Chemical Society | Year: 2014

In a typical battery, the inert electrolyte functions solely as the ionic conductor without contribution to the cell capacity. Here we demonstrate that the most energy-dense Li-CFx battery delivers a capacity exceeding the theoretical maximum of CFx with a solid electrolyte of Li 3PS4 (LPS) that has dual functions: as the inert electrolyte at the anode and the active component at the cathode. Such a bifunctional electrolyte reconciles both inert and active characteristics through a synergistic discharge mechanism of CFx and LPS. The synergy at the cathode is through LiF, the discharge product of CFx, which activates the electrochemical discharge of LPS at a close electrochemical potential of CFx. Therefore, the solid-state Li-CFx batteries output 126.6% energy beyond their theoretic limits without compromising the stability of the cell voltage. The additional energy comes from the electrochemical discharge of LPS, the inert electrolyte. This bifunctional electrolyte revolutionizes the concept of conventional batteries and opens a new avenue for the design of batteries with unprecedented energy density. © 2014 American Chemical Society.

He K.,University of Houston | Babaye Khorasani F.,University of Houston | Retterer S.T.,Center for Nanophase Materials science | Thomas D.K.,Oak Ridge National Laboratory | And 2 more authors.
ACS Nano | Year: 2013

The diffusive dynamics of dilute dispersions of nanoparticles of diameter 200-400 nm were studied in microfabricated arrays of nanoposts using differential dynamic microscopy and single particle tracking. Posts of diameter 500 nm and height 10 μm were spaced by 1.2-10 μm on a square lattice. As the spacing between posts was decreased, the dynamics of the nanoparticles slowed. Moreover, the dynamics at all length scales were best represented by a stretched exponential rather than a simple exponential. Both the relative diffusivity and the stretching exponent decreased linearly with increased confinement and, equivalently, with decreased void volume. The slowing of the overall diffusive dynamics and the broadening distribution of nanoparticle displacements with increased confinement are consistent with the onset of dynamic heterogeneity and the approach to vitrification. © 2013 American Chemical Society.

Balke N.,Center for Nanophase Materials science | Jesse S.,Center for Nanophase Materials science | Kim Y.,Oak Ridge National Laboratory | Adamczyk L.,Oak Ridge National Laboratory | And 3 more authors.
ACS Nano | Year: 2010

We have developed a scanning probe microscopy approach to explore voltage-controlled ion dynamics in ionically conductive solids and decouple transport and local electrochemical reactivity on the nanometer scale. Electrochemical strain microscopy allows detection of bias-induced ionic motion through the dynamic (0.1-1 MHz) local strain. Spectroscopic modes based on low-frequency (∼1 Hz) voltage sweeps allow local ion dynamics to be probed locally. The bias dependence of the hysteretic strain response accessed through first-order reversal curve (FORC) measurements demonstrates that the process is activated at a certain critical voltage and is linear above this voltage everywhere on the surface. This suggests that FORC spectroscopic ESM data separates local electrochemical reaction and transport processes. The relevant parameters such as critical voltage and effective mobility can be extracted for each location and correlated with the microstructure. The evolution of these behaviors with the charging of the amorphous Si anode in a thin-film Li-ion battery is explored. A broad applicability of this method to other ionically conductive systems is predicted. © 2010 American Chemical Society.

Ievlev A.V.,Center for Nanophase Materials science | Ievlev A.V.,Oak Ridge National Laboratory | Alikin D.O.,Ural Federal University | Morozovska A.N.,Ukrainian Academy of Sciences | And 6 more authors.
ACS Nano | Year: 2015

Polarization switching in ferroelectric materials is governed by a delicate interplay between bulk polarization dynamics and screening processes at surfaces and domain walls. Here we explore the mechanism of tip-induced polarization switching at nonpolar cuts of uniaxial ferroelectrics. In this case, the in-plane component of the polarization vector switches, allowing for detailed observations of the resultant domain morphologies. We observe a surprising variability of resultant domain morphologies stemming from a fundamental instability of the formed charged domain wall and associated electric frustration. In particular, we demonstrate that controlling the vertical tip position allows the polarity of the switching to be controlled. This represents a very unusual form of symmetry breaking where mechanical motion in the vertical direction controls the lateral domain growth. The implication of these studies for ferroelectric devices and domain wall electronics are discussed. © 2014 American Chemical Society.

Feng G.,Clemson University | Huang J.,Center for Nanophase Materials science | Sumpter B.G.,Center for Nanophase Materials science | Meunier V.,Rensselaer Polytechnic Institute | Qiao R.,Clemson University
Physical Chemistry Chemical Physics | Year: 2011

Room-temperature ionic liquids (RTILs) have received significant attention as electrolytes due to a number of attractive properties such as their wide electrochemical windows. Since electrical double layers (EDLs) are the cornerstone for the applications of RTILs in electrochemical systems such as supercapacitors, it is important to develop an understanding of the structure-capacitance relationships for the EDLs of these systems. Here we present a theoretical framework termed "counter-charge layer in generalized solvents" (CGS) for describing the structure and capacitance of the EDLs in neat RTILs and in RTILs mixed with different mass fractions of organic solvents. Within this framework, an EDL is made up of a counter-charge layer exactly balancing the electrode charge, and of polarized generalized solvents (in the form of layers of ion pairs, each of which has a zero net charge but has a dipole moment - the ion pairs thus can be considered as a generalized solvent) consisting of all RTILs inside the system except the counter-ions in the counter-charge layer, together with solvent molecules if present. Several key features of the EDLs that originate from the strong ion-ion correlation in RTILs, e.g., overscreening of electrode charge and alternating layering of counter-ions and co-ions, are explicitly incorporated into this framework. We show that the dielectric screening in EDLs is governed predominantly by the polarization of generalized solvents (or ion pairs) in the EDL, and the capacitance of an EDL can be related to its microstructure with few a priori assumptions or simplifications. We use this framework to understand two interesting phenomena observed in molecular dynamics simulations of EDLs in a neat IL of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF 4]) and in a mixture of [BMIM][BF4] and acetonitrile (ACN): (1) the capacitance of the EDLs in the [BMIM][BF4]/ACN mixture increases only slightly when the mass fraction of ACN in the mixture increases from zero to 50% although the dielectric constant of bulk ACN is more than two times higher than that of neat [BMIM][BF4]; (2) the capacitance of EDLs near negative electrodes (with BMIM+ ion as the counter-ion) is smaller than that near positive electrodes (with BF4 - as the counter-ion) although the closest approaches of both ions to the electrode surface are nearly identical. © the Owner Societies 2011.

Lin W.,Center for Nanophase Materials science | Li Q.,Center for Nanophase Materials science | Sales B.C.,Oak Ridge National Laboratory | Jesse S.,Center for Nanophase Materials science | And 3 more authors.
ACS Nano | Year: 2013

The relationship between atomically defined structures and physical properties in functional materials remains a subject of constant interest. We explore the interplay between local crystallographic structure, composition, and local superconductive properties in iron chalcogenide superconductors. Direct structural analysis of scanning tunneling microscopy data allows local lattice distortions and structural defects across an FeTe0.55Se 0.45 surface to be explored on a single unit-cell level. Concurrent superconducting gap (SG) mapping reveals suppression of the SG at well-defined structural defects, identified as a local structural distortion. The strong structural distortion causes the vanishing of the superconducting state. This study provides insight into the origins of superconductivity in iron chalcogenides by providing an example of atomic-level studies of the structure-property relationship. © 2013 American Chemical Society.

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