163 research outputs found
Enhancing Ionic Conductivity of Bulk Single Crystal Yttria-Stabilized Zirconia by Tailoring Dopant Distribution
We present an ab-initio based kinetic Monte Carlo model for ionic
conductivity in single crystal yttria-stabilized zirconia. Ionic interactions
are taken into account by combining density functional theory calculations and
the cluster expansion method and are found to be essential in reproducing the
effective activation energy observed in experiments. The model predicts that
the effective energy barrier can be reduced by 0.15-0.25 eV by arranging the
dopant ions into a super-lattice.Comment: Submitted to Phys. Rev. Lett. on 8/3/2010 (in review
Size-dependent spinodal and miscibility gaps for intercalation in nano-particles
Using a recently-proposed mathematical model for intercalation dynamics in
phase-separating materials [Singh, Ceder, Bazant, Electrochimica Acta 53, 7599
(2008)], we show that the spinodal and miscibility gaps generally shrink as the
host particle size decreases to the nano-scale. Our work is motivated by recent
experiments on the high-rate Li-ion battery material LiFePO4; this serves as
the basis for our examples, but our analysis and conclusions apply to any
intercalation material. We describe two general mechanisms for the suppression
of phase separation in nano-particles: (i) a classical bulk effect, predicted
by the Cahn-Hilliard equation, in which the diffuse phase boundary becomes
confined by the particle geometry; and (ii) a novel surface effect, predicted
by chemical-potential-dependent reaction kinetics, in which
insertion/extraction reactions stabilize composition gradients near surfaces in
equilibrium with the local environment. Composition-dependent surface energy
and (especially) elastic strain can contribute to these effects but are not
required to predict decreased spinodal and miscibility gaps at the nano-scale
Frequency Dependent Dynamical Electromechanical Response of Mixed Ionic-Electronic Conductors
Frequency dependent dynamic electromechanical response of the mixed
ionic-electronic conductor film to a periodic electric bias is analyzed for
different electronic and ionic boundary conditions. Dynamic effects of mobile
ions concentration (stoichiometry contribution), charge state of acceptors
(donors), electron concentration (electron-phonon coupling via the deformation
potential) and flexoelectric effect contribution are discussed. A variety of
possible nonlinear dynamic electromechanical response of MIEC films including
quasi-elliptic curves, asymmetric hysteresis-like loops with pronounced memory
window and butterfly-like curves are calculated. The electromechanical response
of ionic semiconductor is predicted to be a powerful descriptor of local
valence states, band structure and electron-phonon correlations that can be
readily measured in the nanoscale volumes and in the presence of strong
electronic conductivity.Comment: 36 pages, 10 figures, accepted to J. Appl. Phy
The violent youth of bright and massive cluster galaxies and their maturation over 7 billion years
In this study, we investigate the formation and evolution mechanisms of the brightest cluster galaxies (BCGs) over cosmic time. At high redshift (z ∼ 0.9), we selected BCGs and most massive cluster galaxies (MMCGs) from the Cl1604 supercluster and compared them to low-redshift (z ∼ 0.1) counterparts drawn from the MCXC meta-catalogue, supplemented by Sloan Digital Sky Survey imaging and spectroscopy. We observed striking differences in the morphological, colour, spectral, and stellar mass properties of the BCGs/MMCGs in the two samples. High-redshift BCGs/MMCGs were, in many cases, star-forming, late-type galaxies, with blue broad-band colours, properties largely absent amongst the low-redshift BCGs/MMCGs. The stellar mass of BCGs was found to increase by an average factor of 2.51 ± 0.71 from z ∼ 0.9 to z ∼ 0.1. Through this and other comparisons, we conclude that a combination of major merging (mainly wet or mixed) and in situ star formation are the main mechanisms which build stellar mass in BCGs/MMCGs. The stellar mass growth of the BCGs/MMCGs also appears to grow in lockstep with both the stellar baryonic and total mass of the cluster. Additionally, BCGs/MMCGs were found to grow in size, on average, a factor of ∼3, while their average Sérsic index increased by ∼0.45 from z ∼ 0.9 to z ∼ 0.1, also supporting a scenario involving major merging, though some adiabatic expansion is required. These observational results are compared to both models and simulations to further explore the implications on processes which shape and evolve BCGs/MMCGs over the past ∼7 Gyr
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