11 research outputs found
DFT data associated with Set of Small Ordered Structures (SSOS) paper by Kuner, Rothchild, Asta, and Chrzan (2024). https://doi.org/10.1016/j.commatsci.2024.112924
This repository contains a summary of all DFT data used in the paper (https://doi.org/10.1016/j.commatsci.2024.112924), including input parameters, significant outputs, etc.</p
Ab Initio Calculation of Proton Transport in DyPO<sub>4</sub>
Proton mobilities in xenotime-structured
DyPO<sub>4</sub> have
been investigated through first-principles calculations based on electronic
density functional theory. The calculated mobility is shown to be
highly anisotropic, consistent with the tetragonal symmetry of the
xenotime crystal structure. Due to the presence of one-dimensional
channels along the <i>c</i>-axis, the hopping rate is significantly
enhanced along this direction. Specifically, the activation energy
for hopping along the <i>a</i>- and <i>b</i>-axes
is computed to be 0.45 eV away from aliovalent dopant impurities,
while the calculated energy barrier within the channels that run along
the <i>c</i>-axis is 0.15 eV. The corresponding hopping
rates along the <i>c</i>-axis channels are more than 2 orders
of magnitude larger than those calculated previously for the monoclinic
monazite-structured LaPO<sub>4</sub> compound. The effects of aliovalent
dopants on proton migration have also been investigated, considering
the case of Ca<sup>2+</sup> substitution for Dy<sup>3+</sup>. These
calculations reveal a dopant-proton binding energy of approximately
0.4 eV and an increase in the hopping barriers near the dopant by
up to 0.2 eV. These dopant effects were found to be relatively localized,
with minimal changes to the energetics of the protons obtained more
than approximately 5 Ã… away from the aliovalent impurity
A database to enable discovery and design of piezoelectric materials
This JSON-file contains metadata pertaining to the compounds studied in this work and the associated calculated piezoelectric properties
Actinide Dioxides in Water: Interactions at the Interface
A comprehensive understanding of chemical interactions
between water and actinide dioxide surfaces is critical for safe operation
and storage of nuclear fuels. Despite substantial previous research,
understanding the nature of these interactions remains incomplete.
In this work, we combine accurate calorimetric measurements with first-principles
computational studies to characterize surface energies and adsorption
enthalpies of water on two fluorite-structured compounds, ThO<sub>2</sub> and CeO<sub>2</sub>, that are relevant for understanding
the behavior of water on actinide oxide surfaces more generally. We
determine coverage-dependent adsorption enthalpies and demonstrate
a mixed molecular and dissociative structure for the first hydration
layer. The results show a correlation between the magnitude of the
anhydrous surface energy and the water adsorption enthalpy. Further,
they suggest a structural model featuring one adsorbed water molecule
per one surface cation on the most stable facet that is expected to
be a common structural signature of water adsorbed on actinide dioxide
compounds
Computational and Experimental Investigation of Ti Substitution in Li<sub>1</sub>(Ni<sub><i>x</i></sub>Mn<sub><i>x</i></sub>Co<sub>1–2<i>x</i>–<i>y</i></sub>Ti<sub><i>y</i></sub>)O<sub>2</sub> for Lithium Ion Batteries
Aliovalent
substitutions in layered transition-metal cathode materials
has been demonstrated to improve the energy densities of lithium ion
batteries, with the mechanisms underlying such effects incompletely
understood. Performance enhancement associated with Ti substitution
of Co in the cathode material Li<sub>1</sub>(Ni<sub><i>x</i></sub>Mn<sub><i>x</i></sub>Co<sub>1–2<i>x</i></sub>)ÂO<sub>2</sub> were investigated using density functional theory
calculations, including Hubbard-U corrections. An examination of the
structural and electronic modifications revealed that Ti substitution
reduces the structural distortions occurring during delithiation due
to the larger cation radius of Ti<sup>4+</sup> relative to Co<sup>3+</sup> and the presence of an electron polaron on Mn cations induced
by aliovalent Ti substitution. The structural differences were found
to correlate with a decrease in the lithium intercalation voltage
at lower lithium concentrations, which is consistent with quasi-equilibrium
voltages obtained by integrating data from stepped potential experiments.
Further, Ti is found to suppress the formation of a secondary rock
salt phase at high voltage. Our results provide insights into how
selective substitutions can enhance the performance of cathodes, maximizing
the energy density and lifetime of current Li ion batteries
Cerium Substitution in Yttrium Iron Garnet: Valence State, Structure, and Energetics
The garnet structure is a promising
nuclear waste form because
it can accommodate various actinide elements. Yttrium iron garnet,
Y<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub> (YIG), is a model composition
for such substitutions. Since cerium (Ce) can be considered an analogue
of actinide elements such as thorium (Th), plutonium (Pu), and uranium
(U), studying the local structure and thermodynamic stability of Ce-substituted
YIG (Ce:YIG) can provide insights into the structural and energetic
aspects of large ion substitution in garnets. Single phases of YIG
with Ce substitution up to 20 mol % (Y<sub>3–<i>x</i></sub>Ce<sub><i>x</i></sub>Fe<sub>5</sub>O<sub>12</sub> with 0 ≤ <i>x</i> ≤ 0.2) were synthesized
through a citrate–nitrate combustion method. The oxidation
state of Ce was examined by X-ray absorption near edge structure spectroscopy
(XANES); the oxidation state and site occupancy of iron (Fe) as a
function of Ce loading also was monitored by <sup>57</sup>Fe–Mössbauer
spectroscopy. These measurements establish that Ce is predominantly
in the trivalent state at low substitution levels, while a mixture
of trivalent and tetravalent states is observed at higher concentrations.
Fe was predominately trivalent and exists in multiple environments.
High temperature oxide melt solution calorimetry was used to determine
the enthalpy of formation of these Ce-substituted YIGs. The thermodynamic
analysis demonstrated that, although there is an entropic driving
force for the substitution of Ce for Y, the substitution reaction
is enthalpically unfavorable. The experimental results are complemented
by electronic structure calculations performed within the framework
of density functional theory (DFT) with Hubbard-<i>U</i> corrections, which reproduce the observed increase in the tendency
for tetravalent Ce to be present with a higher loading of Ce. The
DFT+<i>U</i> results suggest that the energetics underlying
the formation of tetravalent Ce involve a competition between an unfavorable
energy to oxidize Ce and reduce Fe and a favorable contribution due
to strain-energy reduction. The structural and thermodynamic findings
suggest a strategy to design thermodynamically favorable substitutions
of actinides in the garnet system
Bistable Amphoteric Native Defect Model of Perovskite Photovoltaics
The past few years
have witnessed unprecedented rapid improvement
of the performance of a new class of photovoltaics based on halide
perovskites. This progress has been achieved even though there is
no generally accepted mechanism of the operation of these solar cells.
Here we present a model based on bistable amphoteric native defects
that accounts for all key characteristics of these photovoltaics and
explains many idiosyncratic properties of halide perovskites. We show
that a transformation between donor-like and acceptor-like configurations
leads to a resonant interaction between amphoteric defects and free
charge carriers. This interaction, combined with the charge transfer
from the perovskite to the electron and hole transporting layers results
in the formation of a dynamic <i>n-i-p</i> junction whose
photovoltaic parameters are determined by the perovskite absorber.
The model provides a unified explanation for the outstanding properties
of the perovskite photovoltaics, including hysteresis of <i>J–V</i> characteristics and ultraviolet light-induced degradation
Computational Study of Halide Perovskite-Derived A<sub>2</sub>BX<sub>6</sub> Inorganic Compounds: Chemical Trends in Electronic Structure and Structural Stability
The electronic structure and energetic
stability of A<sub>2</sub>BX<sub>6</sub> halide compounds with the
cubic and tetragonal variants
of the perovskite-derived K<sub>2</sub>PtCl<sub>6</sub> prototype
structure are investigated computationally within the frameworks of
density-functional-theory (DFT) and hybrid (HSE06) functionals. The
HSE06 calculations are undertaken for seven known A<sub>2</sub>BX<sub>6</sub> compounds with A = K, Rb, and Cs; and B = Sn, Pd, Pt, Te,
and X = I. Trends in band gaps and energetic stability are identified,
which are explored further employing DFT calculations over a larger
range of chemistries, characterized by A = K, Rb, Cs, B = Si, Ge,
Sn, Pb, Ni, Pd, Pt, Se, and Te; and X = Cl, Br, I. For the systems
investigated in this work, the band gap increases from iodide to bromide
to chloride. Further, variations in the A site cation influences the
band gap as well as the preferred degree of tetragonal distortion.
Smaller A site cations such as K and Rb favor tetragonal structural
distortions, resulting in a slightly larger band gap. For variations
in the B site in the (Ni, Pd, Pt) group and the (Se, Te) group, the
band gap increases with increasing cation size. However, no observed
chemical trend with respect to cation size for band gap was found
for the (Si, Sn, Ge, Pb) group. The findings in this work provide
guidelines for the design of halide A<sub>2</sub>BX<sub>6</sub> compounds
for potential photovoltaic applications
A Combined Experimental-Computational Study on the Effect of Topology on Carbon Dioxide Adsorption in Zeolitic Imidazolate Frameworks
We report CO<sub>2</sub> adsorption data for four zeolitic
imidazolate
frameworks (ZIFs) to 55 bar, namely ZIF-7, ZIF-11, ZIF-93, and ZIF-94.
Modification of synthetic conditions allows access to different topologies
with the same metal ion and organic link: ZIF-7 (ZIF-94) having <b>sod</b> topology and ZIF-11 (ZIF-93) having the <b>rho</b> topology. The varying topology, with fixed metal ion and imidazolate
functionality, makes these systems ideal for studying the effect of
topology on gas adsorption in ZIFs. The experiments show that the
topologies with the smaller pores (ZIF-7 and 94) have larger adsorptions
than their counterparts (ZIF-11 and 93, respectively) at low pressures
(<1 bar); however, the reverse is true at higher pressures where
the larger-pore structures have significantly higher adsorption. Molecular
modeling and heat of adsorption measurements indicate that while the
binding potential wells for the smaller-pore structures are deeper
than those of the larger-pore structures, they are relatively narrow
and cannot accommodate multiple CO<sub>2</sub> occupancy, in contrast
to the much broader potential wells seen in the larger pore structures
Morphology-Independent Stable White-Light Emission from Self-Assembled Two-Dimensional Perovskites Driven by Strong Exciton–Phonon Coupling to the Organic Framework
Hybrid
two-dimensional (2D) lead halide perovskites have been employed
in optoelectronic applications, including white-light emission for
light-emitting diodes (LEDs). However, until now, there have been
limited reports about white-light-emitting lead halide perovskites
with experimental insights into the mechanism of the broadband emission.
Here, we present white-light emission from a 2D hybrid lead chloride
perovskite, using the widely known phenethylammonium cation. The single-crystal
X-ray structural data, time-resolved photophysical measurements, and
density functional theory calculations are consistent with broadband
emission arising from strong exciton–phonon coupling with the
organic lattice, which is independent of surface defects. The phenethylammonium
lead chloride material exhibits a remarkably high color rendering
index of 84, a CIE coordinate of (0.37,0.42), a CCT of 4426, and photostability,
making it ideal for natural white LED applications