7 research outputs found
ferroelectric search distortion and workflow data and VASP files
<div>The zipped JSON files (distortion.json.gz and workflow_data.json.gz) contain details for each candidate from a search of the Materials Project database for ferroelectrics. These JSON files provide details of the symmetry analysis performed for each candidate and data generated by DFT calculations and post-processing from the workflow (respectively).</div><div><br></div>The zipped folders contain VASP input and output files for ferroelectric search of Materials Project
ferroelectric search misc. mongo databases
<div>These files are included for archiving purposes. They are not intended for the general user.</div><div><br></div>These are compressed tgz folders generated by mongodump for multiple mongodbs used to create the ferroelectric_dataset json files. <div><br></div><div>These databases include the distortion databases generated from Bilbao Crystallographic Server queries, the Fireworks launchpad database (merged from multiple databases), and the full VASP calculation database (merged from multiple).</div><div><br></div><div>loadDBs.sh is included to upload the mongodumps to a mongodb after the files are untarred (tar -xvzf filename.tgz).</div
ferroelectric search distortion and workflow data
These files contain details for each candidate from a search of the Materials Project database for ferroelectrics. These JSON files provide details of the symmetry analysis performed for each candidate and data generated by DFT calculations and post-processing from the workflow
Critical Role of Methylammonium Librational Motion in Methylammonium Lead Iodide (CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>) Perovskite Photochemistry
Raman and photoluminescence
(PL) spectroscopy are used to investigate dynamic structureâfunction
relationships in methylammonium lead iodide (MAPbI<sub>3</sub>) perovskite.
The intensity of the 150 cm<sup>â1</sup> methylammonium (MA)
librational Raman mode is found to be correlated with PL intensities
in microstructures of MAPbI<sub>3</sub>. Because of the strong hydrogen
bond between hydrogens in MA and iodine in the PbI<sub>6</sub> perovskite
octahedra, the Raman activity of MA is very sensitive to structural
distortions of the inorganic framework. The structural distortions
directly influence PL intensities, which in turn have been correlated
with microstructure quality. Our measurements, supported with first-principles
calculations, indicate how excited-state MA librational displacements
mechanistically control PL efficiency and lifetime in MAPbI<sub>3</sub>î¸material parameters that are likely important for efficient
photovoltaic devices
Discovery and Characterization of a Pourbaix-Stable, 1.8 eV Direct Gap Bismuth Manganate Photoanode
Solar-driven oxygen
evolution is a critical technology for renewably
synthesizing hydrogen- and carbon-containing fuels in solar fuel generators.
New photoanode materials are needed to meet efficiency and stability
requirements, motivating materials explorations for semiconductors
with (i) band-gap energy in the visible spectrum and (ii) stable operation
in aqueous electrolyte at the electrochemical potential needed to
evolve oxygen from water. Motivated by the oxygen evolution competency
of many Mn-based oxides, the existence of several Bi-containing ternary
oxide photoanode materials, and the variety of known oxide materials
combining these elements with Sm, we explore the BiâMnâSm
oxide system for new photoanodes. Through the use of a ferri/ferrocyanide
redox couple in high-throughput screening, BiMn<sub>2</sub>O<sub>5</sub> and its alloy with Sm are identified as photoanode materials with
a near-ideal optical band gap of 1.8 eV. Using density functional
theory-based calculations of the mullite Bi<sup>3+</sup>Mn<sup>3+</sup>Mn<sup>4+</sup>O<sub>5</sub> phase, we identify electronic analogues
to the well-known BiVO<sub>4</sub> photoanode and demonstrate excellent
Pourbaix stability above the oxygen evolution Nernstian potential
from pH 4.5 to 15. Our suite of experimental and computational characterization
indicates that BiMn<sub>2</sub>O<sub>5</sub> is a complex oxide with
the necessary optical and chemical properties to be an efficient,
stable solar fuel photoanode
Ferroelectricity in Pb<sub>1+δ</sub>ZrO<sub>3</sub> Thin Films
Antiferroelectric
PbZrO<sub>3</sub> is being considered for a wide
range of applications where the competition between centrosymmetric
and noncentrosymmetric phases is important to the response. Here,
we focus on the epitaxial growth of PbZrO<sub>3</sub> thin films and
understanding the chemistryâstructure coupling in Pb<sub>1+δ</sub>ZrO<sub>3</sub> (δ = 0, 0.1, 0.2). High-quality, single-phase
Pb<sub>1+δ</sub>ZrO<sub>3</sub> films are synthesized via pulsed-laser
deposition. Although no significant lattice parameter change is observed
in X-ray studies, electrical characterization reveals that while the
PbZrO<sub>3</sub> and Pb<sub>1.1</sub>ZrO<sub>3</sub> heterostructures
remain intrinsically antiferroelectric, the Pb<sub>1.2</sub>ZrO<sub>3</sub> heterostructures exhibit a hysteresis loop indicative of
ferroelectric response. Further X-ray scattering studies reveal strong
quarter-order diffraction peaks in PbZrO<sub>3</sub> and Pb<sub>1.1</sub>ZrO<sub>3</sub> heterostructures indicative of antiferroelectricity,
while no such peaks are observed for Pb<sub>1.2</sub>ZrO<sub>3</sub> heterostructures. Density functional theory calculations suggest
the large cation nonstoichiometry is accommodated by incorporation
of antisite Pb<sub>Zr</sub> defects, which drive the Pb<sub>1.2</sub>ZrO<sub>3</sub> heterostructures to a ferroelectric phase with <i>R</i>3<i>c</i> symmetry. In the end, stabilization
of metastable phases in materials via chemical nonstoichiometry and
defect engineering enables a novel route to manipulate the energy
of the ground state of materials and the corresponding material properties
Reducing Coercive-Field Scaling in Ferroelectric Thin Films <i>via</i> Orientation Control
The desire for low-power/voltage
operation of devices is driving
renewed interest in understanding scaling effects in ferroelectric
thin films. As the dimensions of ferroelectrics are reduced, the properties
can vary dramatically, including the robust scaling relationship between
coercive field (<i>E</i><sub>c</sub>) and thickness (<i>d</i>), also referred to as the JanovecâKayâDunn
(JKD) law, wherein <i>E</i><sub>c</sub> â <i>d</i><sup>â2/3</sup>. Here, we report that whereas (001)-oriented
heterostructures follow JKD scaling across the thicknesses range of
20â330 nm, (111)-oriented heterostructures of the canonical
tetragonal ferroelectric PbZr<sub>0.2</sub>Ti<sub>0.8</sub>O<sub>3</sub> exhibit a deviation from JKD scaling wherein a smaller scaling exponent
for the evolution of <i>E</i><sub>c</sub> is observed in
films of thickness Ⲡ165 nm. X-ray diffraction reveals that
whereas (001)-oriented heterostructures remain tetragonal for all
thicknesses, (111)-oriented heterostructures exhibit a transition
from tetragonal-to-monoclinic symmetry in films of thickness â˛
165 nm as a result of the compressive strain. First-principles calculations
suggest that this symmetry change contributes to the deviation from
the expected scaling, as the monoclinic phase has a lower energy barrier
for switching. This structural evolution also gives rise to changes
in the <i>c</i>/<i>a</i> lattice parameter ratio,
wherein this ratio increases and decreases in (001)- and (111)-oriented
heterostructures, respectively, as the films are made thinner. In
(111)-oriented heterostructures, this reduced tetragonality drives
a reduction of the remanent polarization and, therefore, a reduction
of the domain-wall energy and overall energy barrier to switching,
which further exacerbates the deviation from the expected scaling.
Overall, this work demonstrates a route toward reducing coercive fields
in ferroelectric thin films and provides a possible mechanism to understand
the deviation from JKD scaling