Revealing Local Disorder in a Silver-Bismuth Halide Perovskite upon Compression
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Girdzis, Samuel P.↗
Engineering topics
Lin, Yu
Publications and source records attributed to Lin, Yu.
Pressure-induced excimer formation and fluorescence enhancement of an anthracene derivative
Excimer materials have been widely studied and have generated significant interest for their applications in many optoelectronic devices. However, a thorough investigation of the entire process involved in excimer formation, enhancement, and annihilation in solid materials is still lacking. Here we designed a crystal based on an anthracene derivative with dissociative, molecular-ordered dimer assembly, and studied the formation and evolution of an anthracene excimer as a function of pressure. During the initial stage of pressurization, the fluorescence intensity arising from anthracene monomers gradually decreases. Therefore, with continued compression, the two anthracene units become increasingly closer allowing strong intermolecular π–π interactions to develop that lead to excimer formation at 3.5 GPa, accompanied with a phase transition. The fluorescence intensity then keeps increasing with pressure and reaches its maximum at 5.6 GPa due to the strengthening of the excimer and the increased structural defects. Meanwhile the fluorescence color shows a continuous redshift, which initially results from conformation planarization and then excimer evolution. After releasing pressure back to ambient conditions, the structural changes in the sample are reversible, while the fluorescence signal preserves some high-pressure features due to the partial retention of the π–π interactions between the anthracene dimers. This study reveals the evolution of an excimer and its intrinsic photophysical properties, and provides guidance for future research on pressure-sensitive fluorescent devices.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
CALPHAD Uncertainty Quantification and TDBX
CALPHAD uncertainty quantification (UQ) is the foundation of materials design with quantified confidence. We report a framework and software packages to enable CALPHAD UQ assessment and calculation using commercial CALPHAD software (Thermo-Calc). This Bayesian inference framework is coupled with a Markov chain Monte Carlo algorithm to establish uncertainty traces with a given thermodynamic database file (TDB) and corresponding experimental data points. This general framework is demonstrated with the Ni–Cr binary system. The algorithm is firstly validated on synthetic data with known ground truth. Then it is applied to real experimental data to generate posterior traces. We develop a file format named TDBX, which provides a single source of truth by combining the original TDB content and the traces for each assessed Gibbs energy parameter. CALPHAD UQ calculations are performed based on the TDBX file, from which uncertainties for phase boundaries, enthalpy curves, and solidification range are collected as examples of basic design parameters. This TDBX file with corresponding scripts are made open-source. Finally, the combination of CALPHAD UQ assessments and calculations connected by TDBX supports uncertainty-assisted modeling, enabling the integrated application of modern design with uncertainty methodologies to computational materials design.
36 MATERIALS SCIENCE↗
Magnetopause Reconnection as Influenced by the Dipole Tilt Under Southward IMF Conditions: Hybrid Simulation and MMS Observation
Abstract Using a three‐dimensional (3‐D) global‐scale hybrid code, the Magnetospheric Multiscale (MMS) reconnection event around 02:13 UT on 18 November 2015, highlighted in the Geospace Environment Modeling (GEM) Dayside Kinetic Challenge, is simulated, in which the interplanetary magnetic field (IMF) points southward and the geomagnetic field has a −27° dipole tilt angle. Strong southward plasma jets are found near the magnetopause as a result of the dayside reconnection. Our results indicate that the subsolar magnetopause reconnection X line shifts from the subsolar point toward the Northern Hemisphere due to the effect of the tilted geomagnetic dipole angle, consistent with the MMS observation. Subsequently, the reconnection X lines or sites and reconnection flux ropes above the equator propagate northward along the magnetopause. The formation and global distribution of the X lines and the structure of the magnetopause reconnection are investigated in detail with the simulation. Mirror mode waves are also found in the middle of the magnetosheath downstream of the quasi‐perpendicular shock where the plasma properties are consistent with the mirror instability condition. As a special outcome of the GEM challenge event, the spatial and temporal variations in reconnection, the electromagnetic power spectra, and the associated D‐shaped ion velocity distributions in the simulated reconnection event are compared with the MMS observation.
Guo, Zhifang↗
Pressure Effects on the Electronic and Optical Properties in Low-Dimensional Metal Halide Perovskites
Metal halide perovskites have shown enormous potential in perovskite solar cells and light-emitting diodes and made unprecedented progress in the past decade. Additionally, pressure engineering as an effective technique can systematically modify the electronic structures and physical properties of functional materials. Low-dimensional metal halide perovskites (0D, 1D, and 2D) with a variety of compositions have soft lattices that allow pressure to drastically modulate their structures and properties. High-pressure investigations have obtained a comprehensive understanding of their structure–property relationships. Simultaneously, discoveries of novel pressure-driven properties, such as metallization and partially retained band gap narrowing have contributed significantly to the further development of such materials. In this work, we mainly highlight the effect of pressure on the properties and structures of low-dimensional metal halide perovskites, which is essential for designing new perovskite materials and advancing applications.
36 MATERIALS SCIENCE↗
Origins of the Pressure-Induced Phase Transition and Metallization in the Halide Perovskite (CH 3 NH 3 )PbI 3
Hybrid halide perovskites are promising for applications because of their favorable optoelectronic properties and low cost. Here we investigate the effects of hydrostatic pressure on the structural and electronic properties of (MA)PbI 3 (MA = CH 3 NH 3 + ) using first-principles density functional theory calculations. Our calculations predict that at a pressure of 0.23 GPa, the orthorhombic Fmmm phase becomes unstable with respect to a cubic Im$\bar{3}$ phase, in good agreement with room-temperature experiments (~0.3 GPa). At higher pressures, about 6 GPa, we predict the onset of pronounced intra- and interoctahedral distortions. This symmetry lowering leads to the introduction of I 5p–I 5p* antibonding and Pb 6p–Pb 6p bonding character into the valence band maximum (VBM) and the conduction band minimum (CBM) states, respectively. We find this change in bond character explains the evolution of the VBM and CBM states under compression, trends that ultimately lead to metallization at significantly higher pressures.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Facile diamond synthesis from lower diamondoids
Carbon-based nanomaterials have exceptional properties that make them attractive for a variety of technological applications. Here, we report on the use of diamondoids (diamond-like, saturated hydrocarbons) as promising precursors for laser-induced high-pressure, high-temperature diamond synthesis. The lowest pressure and temperature $(P-T)$ conditions that yielded diamond were 12 GPa (at ~2000 K) and 900 K (at ~20 GPa), respectively. This represents a substantially reduced transformation barrier compared with diamond synthesis from conventional (hydro)carbon allotropes, owing to the similarities in the structure and full sp 3 hybridization of diamondoids and bulk diamond. At 20 GPa, diamondoid-to-diamond conversion occurs rapidly within <19 μs. Molecular dynamics simulations indicate that once dehydrogenated, the remaining diamondoid carbon cages reconstruct themselves into diamond-like structures at high $P-T$. This study is the first successful mapping of the $P-T$ conditions and onset timing of the diamondoid-to-diamond conversion and elucidates the physical and chemical factors that facilitate diamond synthesis.
36 MATERIALS SCIENCE↗
High Compression‐Induced Conductivity in a Layered Cu–Br Perovskite
Abstract We show that the onset pressure for appreciable conductivity in layered copper‐halide perovskites can decrease by ca. 50 GPa upon replacement of Cl with Br. Layered Cu–Cl perovskites require pressures >50 GPa to show a conductivity of 10 −4 S cm −1 , whereas here a Cu–Br congener, (EA) 2 CuBr 4 (EA=ethylammonium), exhibits conductivity as high as 2×10 −3 S cm −1 at only 2.6 GPa, and 0.17 S cm −1 at 59 GPa. Substitution of higher‐energy Br 4p for Cl 3p orbitals lowers the charge‐transfer band gap of the perovskite by 0.9 eV. This 1.7 eV band gap decreases to 0.3 eV at 65 GPa. High‐pressure X‐ray diffraction, optical absorption, and transport measurements, and density functional theory calculations allow us to track compression‐induced structural and electronic changes. The notable enhancement of the Br perovskite's electronic response to pressure may be attributed to more diffuse Br valence orbitals relative to Cl orbitals. This work brings the compression‐induced conductivity of Cu‐halide perovskites to more technologically accessible pressures.
Jaffe, Adam↗
Pressure‐Induced Emission (PIE) and Phase Transition of a Two‐dimensional Halide Double Perovskite (BA) 4 AgBiBr 8 (BA=CH 3 (CH 2 ) 3 NH 3 + )
Abstract Two‐dimensional (2D) halide perovskites have attracted significant attention due to their compositional flexibility and electronic diversity. Understanding the structure–property relationships in 2D double perovskites is essential for their development for optoelectronic applications. In this work, we observed the emergence of pressure‐induced emission (PIE) at 2.5 GPa with a broad emission band and large Stokes shift from initially nonfluorescent (BA) 4 AgBiBr 8 (BA=CH 3 (CH 2 ) 3 NH 3 + ). The emission intensity increased significantly upon further compression up to 8.2 GPa. Moreover, the band gap narrowed from the starting 2.61 eV to 2.19 eV at 25.0 GPa accompanied by a color change from light yellow to dark yellow. Analysis of combined in situ high‐pressure photoluminescence, absorption, and angle‐dispersive X‐ray diffraction data indicates that the observed PIE can be attributed to the emission from self‐trapped excitons. This coincides with [AgBr 6 ] 5− and [BiBr 6 ] 3− inter‐octahedral tilting which cause a structural phase transition. High‐pressure study on (BA) 4 AgBiBr 8 sheds light on the relationship between the structure and optical properties that may improve the material's potential applications in the fields of pressure sensing, information storage and trademark security.
Fang, Yuanyuan↗
Pressure‐Induced Emission (PIE) and Phase Transition of a Two‐dimensional Halide Double Perovskite (BA) 4 AgBiBr 8 (BA=CH 3 (CH 2 ) 3 NH 3 + )
Abstract Two‐dimensional (2D) halide perovskites have attracted significant attention due to their compositional flexibility and electronic diversity. Understanding the structure–property relationships in 2D double perovskites is essential for their development for optoelectronic applications. In this work, we observed the emergence of pressure‐induced emission (PIE) at 2.5 GPa with a broad emission band and large Stokes shift from initially nonfluorescent (BA) 4 AgBiBr 8 (BA=CH 3 (CH 2 ) 3 NH 3 + ). The emission intensity increased significantly upon further compression up to 8.2 GPa. Moreover, the band gap narrowed from the starting 2.61 eV to 2.19 eV at 25.0 GPa accompanied by a color change from light yellow to dark yellow. Analysis of combined in situ high‐pressure photoluminescence, absorption, and angle‐dispersive X‐ray diffraction data indicates that the observed PIE can be attributed to the emission from self‐trapped excitons. This coincides with [AgBr 6 ] 5− and [BiBr 6 ] 3− inter‐octahedral tilting which cause a structural phase transition. High‐pressure study on (BA) 4 AgBiBr 8 sheds light on the relationship between the structure and optical properties that may improve the material's potential applications in the fields of pressure sensing, information storage and trademark security.
Fang, Yuanyuan↗
Generation of kinetic Alfvén waves in dayside magnetopause reconnection: A 3-D global-scale hybrid simulation
In this paper, we perform a three-dimensional (3-D) global-scale hybrid simulation to investigate the generation of kinetic Alfvén waves (KAWs) in reconnection at the dayside magnetopause. In the simulation, the magnetopause reconnection takes place due to a self-consistent interaction between the solar wind and Earth's magnetosphere, in which the solar wind is assumed to carry a southward interplanetary magnetic field. As multiple X-line reconnection occurs, shear Alfvénic perturbations are generated from reconnection, which propagate toward polar regions along the magnetic field lines. Our detailed analysis of the electromagnetic characteristics reveals the existence of kinetic Alfvén waves on the ion kinetic scales in these perturbations, in which the parallel electric field is generated. The 3-D structures and the Poynting fluxes in the shear Alfvén waves/KAWs in the global magnetopause are presented. It is shown that these KAWs carry electromagnetic energy into the cusp, which may lead to aurora brightening.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Tuning Optical and Electronic Properties in Low-Toxicity Organic–Inorganic Hybrid (CH 3 NH 3 ) 3 Bi 2 I 9 under High Pressure
Low-toxicity, air-stable methylammonium bismuth iodide (CH 3 NH 3 ) 3 Bi 2 I 9 has been proposed as a candidate to replace lead-based perovskites as highly efficient light absorbers for photovoltaic devices. Here, we investigated the effect of pressure on the optoelectronic properties and crystal structure of (CH 3 NH 3 ) 3 Bi 2 I 9 up to 65 GPa at room temperature. We achieved impressive photoluminescence enhancement and band gap narrowing over a moderate pressure range. Dramatic piezochromism from transparent red to opaque black was observed in a single crystal sample. A structural phase transition from hexagonal P6 3 / mmc to monoclinic P21 at 5.0 GPa and completely reversible amorphization at 29.1 GPa were determined by in situ synchrotron X-ray diffraction. Moreover, the dynamically disordered MA + organic cations in the hexagonal phase became orientationally ordered upon entering into the monoclinic phase, followed by static disorder upon amorphization. The striking enhancement of conductivity and metallization under high pressure indicate wholly new electronic properties.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Magnetosheath Reconnection Before Magnetopause Reconnection Driven by Interplanetary Tangential Discontinuity: A Three‐Dimensional Global Hybrid Simulation With Oblique Interplanetary Magnetic Field
Abstract Terrestrial dayside dynamics associated with a southward turning, oblique interplanetary magnetic field (IMF) carried by an interplanetary tangential discontinuity (TD) is investigated by performing a three‐dimensional global‐scale hybrid simulation systematically for cases in which the incoming solar wind TD possesses various magnetic field rotation angles ΔΦ = 90° to 180° and half widths w = 2 d i 0 to w = 30 d i 0 , where d i 0 is the ion inertial length in the solar wind. Overall, the TD is compressed while being transmitted into the magnetosheath, with different compression processes downstream of the quasi‐parallel (Q‐||) and quasi‐perpendicular (Q‐ ⊥ ) shocks. It is found that magnetosheath reconnection may take place downstream of both the Q‐|| and Q‐ ⊥ shocks due to interaction of the directional TD with the bow shock and magnetopause, but the existence of magnetosheath reconnection depends on w and ΔΦ . Magnetosheath flux ropes are formed through three‐dimensional patchy reconnection in the thinned current sheet, with a longer rope lengths under a larger ΔΦ . There exists a dawn‐dusk asymmetry in the spatial extent of the flux ropes, which becomes more significant as ΔΦ decreases. When ΔΦ decreases to 90° , no reconnection flux ropes are found. Magnetopause reconnection is initiated when the magnetic fluxes with a southward turning IMF (on the sunward side) reach the magnetopause, and the magnetopause flux ropes can be mixed with the magnetosheath ones. Our simulation demonstrates that the effects of a southward turning of the IMF may not be a simple field direction change that leads to reconnection only at the magnetopause.
Guo, Zhifang↗
Energy transfer and tunable emission of Ca14Al10Zn6O35:Bi3+,Sm3+ phosphor
Highlights: • We have firstly synthesized a single-phased Ca{sub 14}Al{sub 10}Zn{sub 6}O{sub 35}:Bi{sup 3+},Sm{sup 3+} phosphor. • Different measurement support the energy transfer from Bi{sup 3+} to Sm{sup 3+}. • Based on the energy transfer, tunable emission were realized. - Abstract: A series of Bi{sup 3+}, Sm{sup 3+}-codoped Ca{sub 14}Al{sub 10}Zn{sub 6}O{sub 35} phosphors were synthesized via conventional high temperature solid-state method. The crystal structure, morphology, photoluminescence and energy transfer mechanism from Bi{sup 3+} to Sm{sup 3+} were investigated in detail. A broad blue emission band due to {sup 3}P{sub 1} → {sup 1}S{sub 0} transition of Bi{sup 3+} was observed in the Bi{sup 3+} single-doped Ca{sub 14}Al{sub 10}Zn{sub 6}O{sub 35} sample, the Ca{sup 2+} position are verified to be replaced by Bi{sup 3+} and the corresponding concentration quenching mechanism was dipole-dipole interaction. The considerable spectral overlap between the broad emission band of Bi{sup 3+} around 350–550 nm and the excitation band of Sm{sup 3+} supports the energy transfer from Bi{sup 3+} to Sm{sup 3+}. This investigation will contribute to the comprehension of interactions between Bi{sup 3+} and Sm{sup 3+}. These results reveal the potential application of Bi{sup 3+}, Sm{sup 3+} co-doped phosphor in UV light-emitting diodes and artificial light in plant.
36 MATERIALS SCIENCE↗
Sterically controlled mechanochemistry under hydrostatic pressure
Mechanical stimuli can modify the energy landscape of chemical reactions and enable reaction pathways, offering a synthetic strategy that complements conventional chemistry. These mechanochemical mechanisms have been studied extensively in one-dimensional polymers under tensile stress using ring-opening and reorganization, polymer unzipping and disulfide reduction as model reactions. In these systems, the pulling force stretches chemical bonds, initiating the reaction. Additionally, it has been shown that forces orthogonal to the chemical bonds can alter the rate of bond dissociation. Furthermore, these bond activation mechanisms have not been possible under isotropic, compressive stress (that is, hydrostatic pressure). Here we show that mechanochemistry through isotropic compression is possible by molecularly engineering structures that can translate macroscopic isotropic stress into molecular-level anisotropic strain.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗