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 (CH₃NH₃PbI₃) Perovskite Photochemistry

Raman and photoluminescence (PL) spectroscopy are used to investigate dynamic structure–function relationships in methylammonium lead iodide (MAPbI₃) perovskite. The intensity of the 150 cm^–1 methylammonium (MA) librational Raman mode is found to be correlated with PL intensities in microstructures of MAPbI₃. Because of the strong hydrogen bond between hydrogens in MA and iodine in the PbI₆ 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 MAPbI₃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 Bi–Mn–Sm oxide system for new photoanodes. Through the use of a ferri/ferrocyanide redox couple in high-throughput screening, BiMn₂O₅ 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 Bi³⁺Mn³⁺Mn⁴⁺O₅ phase, we identify electronic analogues to the well-known BiVO₄ 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 BiMn₂O₅ is a complex oxide with the necessary optical and chemical properties to be an efficient, stable solar fuel photoanode

Ferroelectricity in Pb_1+δZrO₃ Thin Films

Antiferroelectric PbZrO₃ 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 PbZrO₃ thin films and understanding the chemistry–structure coupling in Pb_1+δZrO₃ (δ = 0, 0.1, 0.2). High-quality, single-phase Pb_1+δZrO₃ 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 PbZrO₃ and Pb_1.1ZrO₃ heterostructures remain intrinsically antiferroelectric, the Pb_1.2ZrO₃ heterostructures exhibit a hysteresis loop indicative of ferroelectric response. Further X-ray scattering studies reveal strong quarter-order diffraction peaks in PbZrO₃ and Pb_1.1ZrO₃ heterostructures indicative of antiferroelectricity, while no such peaks are observed for Pb_1.2ZrO₃ heterostructures. Density functional theory calculations suggest the large cation nonstoichiometry is accommodated by incorporation of antisite Pb_Zr defects, which drive the Pb_1.2ZrO₃ 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>_c) and thickness (<i>d</i>), also referred to as the Janovec–Kay–Dunn (JKD) law, wherein <i>E</i>_c ∝ <i>d</i>^–2/3. Here, we report that whereas (001)-oriented heterostructures follow JKD scaling across the thicknesses range of 20–330 nm, (111)-oriented heterostructures of the canonical tetragonal ferroelectric PbZr_0.2Ti_0.8O₃ exhibit a deviation from JKD scaling wherein a smaller scaling exponent for the evolution of <i>E</i>_c is observed in films of thickness ≲ 165 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 ≲ 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