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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Observation of Surface-Bound Negatively Charged Hydride and Hydroxide on GaP(110) in H 2 O Environments

Surface-bound species on GaP(110) formed upon interaction with water were investigated through experiment and theory. These studies are motivated by and discussed in the context of electrocatalytic and photoelectrocatalytic schemes for solar fuel production, including especially observations of selective CO 2 reduction to methanol in acidified aqueous solutions of CO 2 and nitrogen-containing heteroaromatics. Experimentally, surface-bound species over ten orders of magnitude of pressure were spectroscopically identified in situ using synchrotron-based ambient pressure photoelectron spectroscopy (APPES). Ga 3d and O 1s core-level spectra indicate that the interaction of GaP(110) with H 2 O induces formation of a partially dissociated adlayer, characterized by the presence of both Ga-OH and molecular H 2 O species. Measurements of the P 2p core level indicate formation of a negatively charged hydride that irreversibly bonds to surface P in vacuum. The surface densities of the hydroxide and hydride species increase with increasing pressure (surface coverage) of water. Periodic slab calculations using density functional theory were used to study several relevant water configurations at 298 K on this surface. Consistent with earlier theoretical predictions at 0 K, the calculations confirm that Ga-OH, molecular H 2 O, and P-H species are thermodynamically stable on the GaP(110) surface under experimental conditions. Isobaric measurements at elevated pressures were used to probe the thermal stabilities of adsorbed species as well as the oxidation of surface Ga and P. The observation of stable surface hydride formation induced by interaction with water is especially notable given the critical role of hydride transfer to catalysts and CO 2 during chemical fuel synthesis reactions in aqueous environments. Furthermore, it is hypothesized that the observed high stability of the hydride on GaP may contribute to its associated remarkable near-100% faradaic efficiency for methanol generation by solar-driven CO 2 reduction in acidified aqueous pyridine solutions [J. Am. Chem. Soc. 2008, 130, 6342], because such stability is known to yield high overpotentials for the competing hydrogen evolution reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Identifying the Interactions That Allow Separation of O 2 from N 2 on the Open Iron Sites of Fe 2 (dobdc)

The presence of open metal sites along with a high porosity makes the Fe 2 (dobdc) metal–organic framework, also called Fe-MOF-74, particularly well suited for separating gaseous mixtures. For instance, since Fe 2 (dobdc) adsorbs O 2 more strongly than N 2 , it can, in principle, be used to separate O 2 from air [Bloch et al., J. Am. Chem. Soc. 2011, 133, 14814]. Here, in the present work, we investigate the reversible differential adsorption of N 2 and O 2 on Fe 2 (dobdc) with Kohn-Sham density functional theory applied to an 88-atom cluster model of the MOF. The cluster is chosen such that it is large enough to allow an accurate description of the most important contributions to the binding enthalpies and small enough to perform high-level quantum mechanical calculations. For the quantum mechanical calculations, we use well-validated exchange–correlation functionals to study the ground-state structures of the Fe–N 2 and Fe–O 2 interacting systems. The calculations agree with experiment in that O 2 binds more strongly than N 2 , and they reveal that the ground-state structure of the Fe–O 2 subsystem has the dioxygen unit in a triplet spin state ferromagnetically coupled to the high-spin state (quintet state) of the iron center. Charge Model 5 (CM5) calculations have been performed to determine the partial atomic charges on the adsorbate molecules and the iron atom, and they show that charge transfer from the open iron(II) site is more important in the case of O 2 than in the case of N 2 . Furthermore, bond orders, vibrational frequencies, and orbital energies were calculated to rationalize the stronger binding of O 2 compared to N 2 on Fe 2 (dobdc).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Revisiting Anisotropic Diffusion of Carbon Dioxide in the Metal–Organic Framework Zn 2 (dobpdc)

The diffusion of gases confined in nanoporous materials underpins membrane and adsorption-based gas separations, yet relatively few measurements of diffusion coefficients in the promising class of materials, metal–organic frameworks (MOFs), have been reported to date. Recently we reported self-diffusion coefficients for 13 CO 2 in the MOF Zn 2 (dobpdc) (dobpdc 4– = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) which has one-dimensional channels with a diameter of approximately 2 nm [Forse, A. C.; J. Am. Chem. Soc. 2018, 140, 1663-1673]. By analyzing the evolution of the residual 13 C chemical shift anisotropy line shape at different gradient strengths, we obtained self-diffusion coefficients both along (D ∥ ) and between (D ⊥ ) the one-dimensional MOF channels. The observation of nonzero D ⊥ was unexpected based on the single crystal X-ray diffraction structure and flexible lattice molecular dynamics simulations, and we proposed that structural defects may be responsible for self-diffusion between the MOF channels. In this paper we revisit this analysis and show that homogeneous line broadening must be taken into account to obtain accurate values for D ⊥ . In the presence of homogeneous line broadening, intensity at a particular NMR frequency represents signal from crystals with a range of orientations relative to the applied magnetic field and magnetic gradient field. To quantify these effects, we perform spectral simulations that take into account homogeneous broadening and allow improved D ⊥ values to be obtained. Finally, our new analysis best supports nonzero D ⊥ at all studied dosing pressures and shows that our previous analysis overestimated D ⊥ .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Electrochemical Behavior of Nanoporous Supercapacitors with Oligomeric Ionic Liquids

According to a recent study [Matsumoto, M. ; J. Am. Chem. Soc. 2017, 139, 16072-16075], an oligomeric ionic liquid (OIL) may exhibit a wide electrochemical window and an exceptionally high capacitance in electric double layer (EDL) transistors. However, little is known on applicability of OILs in EDL capacitors with porous electrodes. To understand the capacitive performance of OILs, here we investigate the charging behavior, EDL structure, and capacitance for different types of OILs using the classical density functional theory. In contrast to their application to field-effect transistors, the capacitive performance of OILs in nanoporous electrodes is sensitive to the charging potential. We report that although adoption of oligomeric cations shows little advantage for the electrical charging of a positive electrode, they enhance the energy storage density for negative electrodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Molecular Picture of the Transient Nature of Lipid Rafts

In biological membranes, lipid rafts are now thought to be transient and nanoscopic. However, the mechanism responsible for these nanoscopic assemblies remains poorly understood, even in the case of model membranes. Therefore, it has proven extremely challenging to probe the physicochemical properties of lipid rafts at the molecular level. Here, we use all-atom molecular dynamics (MD) simulations and inelastic X-ray scattering (IXS), an intrinsically nanoscale technique, to directly probe the energy transfer and collective short-wavelength dynamics (phonons) of biologically relevant model membranes. We show that the nanoscale propagation of stress in lipid rafts takes place in the form of collective motions made up of longitudinal (compression waves) and transverse (shear waves) molecular vibrations. Importantly, we provide a molecular picture for the so-called van der Waals mediated "force from lipid" [Anishkin, A. et al. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 7898], a key parameter for the ionic channel mechano-transduction and the mechanism for the lipid transfer of molecular level stress [Aponte-Santamaría, C. et al. J. Am. Chem. Soc. 2017, 139, 13588]. Specifically, we describe how lipid rafts are formed and maintained through the propagation of molecular stress, lipid raft rattling dynamics, and a relaxation process. Eventually, the rafts dissipate through the self-diffusion of lipids making up the rafts. We also show that the molecular stress and viscoelastic properties of transient lipid rafts can be modulated through the use of hydrophobic biomolecules such as melatonin and tryptophan. Overall, the herein proposed mechanism describing the molecular interactions for the formation and dissolution of lipid rafts may offer insights as to how lipid rafts enable biological function.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Topological Superconductivity Based on Antisymmetric Spin–Orbit Coupling

Topological superconductivity (TSC) has drawn much attention for its fundamental interest and application in quantum computation. An outstanding challenge is the lack of intrinsic TSC materials with a p-wave pairing gap, which has led to the development of an effective p-wave theory of coupling s-wave gap with Rashba spin–orbit coupling (RSOC). However, the RSOC-strict mechanism and materials pose still both fundamental and practical limitations. Here, we generalize this theory to antisymmetric SOC (ASOC). Using k·p perturbation theory, we demonstrate that 2D crystals, with point groups of C 2 , C 4 , C 6 , C 2v , C 4v , C 6v , D 2 , D 4 , D 6 , S 4 , or D 2d , can all facilitate the desired ASOC. Remarkably, this enables us to discover 314 TSC candidates by screening 2D material databases, which are further confirmed by first-principles calculations of Majorana boundary modes and the topological invariant of the superconducting gap. As a result, our work fundamentally enriches TSC theory and greatly expands the classes of TSC materials for experimental exploration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Stacking-dependent interlayer coupling in trilayer MoS 2 with broken inversion symmetry

The stacking configuration in few-layer two-dimensional (2D) materials results in different structural symmetries and layer-to-layer interactions, and hence it provides a very useful parameter for tuning their electronic properties. For example, ABA-stacking trilayer graphene remains semimetallic similar to that of monolayer, while ABC-stacking is predicted to be a tunable band gap semiconductor under an external electric field. Such stacking dependence resulting from many-body interactions has recently been the focus of intense research activities. Here we demonstrate that few-layer MoS 2 samples grown by chemical vapor deposition with different stacking configurations (AA, AB for bilayer; AAB, ABB, ABA, AAA for trilayer) exhibit distinct coupling phenomena in both photoluminescence and Raman spectra. By means of ultralow-frequency (ULF) Raman spectroscopy, we demonstrate that the evolution of interlayer interaction with various stacking configurations correlates strongly with layer-breathing mode (LBM) vibrations. Our ab initio calculations reveal that the layer-dependent properties arise from both the spin–orbit coupling (SOC) and interlayer coupling in different structural symmetries. Lastly, such detailed understanding provides useful guidance for future spintronics fabrication using various stacked few-layer MoS 2 blocks.

36 MATERIALS SCIENCE↗
DOE OSTI2024

An All-Soluble Fe/Mn-Based Alkaline Redox Flow Battery System

Redox flow batteries (RFBs) are membrane-separated rechargeable flow cells with redox electrolytes, offering the potential for large-scale energy storage and supporting renewable energy grids. Yet, creating a cost-effective, high-performance RFB system is challenging. In this work, we investigate an Fe/Mn RFB alkaline system based on the [(TEA)Fe–O–Fe(TEA)] 3– / 4– and MnO 4 – / 2– redox couples with a theoretical cell voltage of ~1.43 V. This combination has not been systematically studied previously, but it can lead to a very low-cost and sustainable materials for high energy storage. Constant current cycling tests were performed at ±41 mA cm –2 between 20% and 80% SOC over 800 h (400 cycles) with an apparent Coulombic efficiency (CE) approaching 100%, while the voltage efficiency (VE) gradually decreased from ~75.3% to ~61.4% due to increasing internal resistances. Finally, the voltage efficiency loss can be mitigated through a periodic acid treatment to remove MnO 2 deposits from the separator.

25 ENERGY STORAGE↗
DOE OSTI2024

Lithium Plating Characteristics in High Areal Capacity Li-Ion Battery Electrodes

Li-ion battery degradation and safety events are often attributed to undesirable metallic lithium plating. Since their release, Li-ion battery electrodes have been made progressively thicker to provide a higher energy density. However, the propensity for plating in these thicker pairings is not well understood. Herein, we combine an experimental plating-prone condition with robust mesoscale modeling to examine electrode pairings with capacities ranging from 2.5 to 6 mAh/cm 2 and negative to positive (N/P) electrode areal capacity ratio from 0.9 to 1.8 without the need for extensive aging tests. Using both experimentation and a mesoscale model, we identify a shift from conventional high state-of-charge (SOC) type plating to high overpotential (OP) type plating as electrode thickness increases. Further, these two plating modes have distinct morphologies, identified by optical microscopy and electrochemical signatures. We demonstrate that under operating conditions where these plating modes converge, a high propensity of plating exists, revealing the importance of predicting and avoiding this overlap for a given electrode pairing. Further, we identify that thicker electrodes, beyond a capacity of 3 mAh/cm 2 or thickness >75 μm, are prone to high OP, limiting negative electrode (NE) utilization and preventing cross-sectional oversizing the NE from mitigating plating. Here, it simply contributes to added mass and volume. The experimental thermal gradient and mesoscale model either combined or independently provide techniques capable of probing performance and safety implications of mild changes to electrode design features.

25 ENERGY STORAGE↗
DOE OSTI2021

Mechanism and kinetics of light alkane dehydrogenation and cracking over isolated Ga species in Ga/H-MFI

The objective of this study is to examine the mechanisms and kinetics of C2H6 dehydrogenation and n-C4H10 dehydrogenation and cracking over isolated Ga species in Ga/HMFI and to compare these results to those reported previously for C3H8 dehydrogenation and cracking. C2H6 dehydrogenation is found to be catalyzed by both [GaH]2+ and [GaH2]+ cations at similar turnover frequencies. Rate measurements over Ga/H-MFI containing predominantly [GaH2]+ cations reveal that C2H6 dehydrogenation rates exhibit a Langmuir.Hinshelwood dependence on C2H6 partial pressure at elevated temperatures (>730 K), consistent with the involvement of chemisorbed [C2H5.GaH]+ species. The reaction kinetics suggest that C2H6 dehydrogenation proceeds via heterolytic C-H cleavage of adsorbed C2H6 by [GaH2]+ cations to form H2 and [C2H5-GaH]+ species, which further decompose via β-hydride elimination to form C2H4. By contrast, C4H10 dehydrogenation and both terminal and central cracking are catalyzed exclusively by [GaH]2+ cations. All three reactions exhibit a Langmuir-Hinshelwood dependence on C4H10 partial pressure and are inhibited by H2. Ratios of dehydrogenation to cracking (total) and terminal to central cracking are approximately independent of C4H10 partial pressure consistent with the involvement of a common C4H10-derived surface intermediate. The observed reaction kinetics are consistent with an alkyl-mediated mechanism occurring over [GaH]2+, analogous to that reported previously for C3H8 dehydrogenation/cracking over Ga/H-MFI (Phadke, N. M.; et al. J. Am. Chem. Soc. 2019, 141, 1614-1627). The mechanism proceeds via facile, heterolytic dissociation of adsorbed C4H10 to form [C4H9-GaH]+-H+ cation pairs via methyl C-H-activated pathways. Dehydrogenation then proceeds via β-hydride elimination, respectively, forming butene, while terminal and central cracking proceed via C-H-activated H+ attack. Methylene activation was also considered but found to occur at a significantly lower rate. Theoretical analysis of the proposed reaction pathways leads to apparent activation enthalpies in good agreement with values extracted from the measured kinetics, thereby supporting the proposed pathways and the roles of [GaH]2+ and [GaH2]+ cations in the dehydrogenation and cracking of light alkanes on Ga/H-MFI.

Phadke, NM↗
DOE OSTI2022

Kinetic Model for the Reduction of Cu II Sites by NO + NH 3 and Reoxidation of NH 3 -Solvated Cu I Sites by O 2 and NO in Cu-SSZ-13

In this work, a kinetic model is developed for the reduction of Cu II sites by NO + NH 3 and the reoxidation of NH 3 -solvated Cu I sites by O 2 and NO in Cu-SSZ-13. Fourier transform infrared (FTIR) spectroscopy and spatially resolved capillary inlet mass spectrometry (SpaciMS) measurements during transient reactor experiments are utilized to identify the rate parameters associated with NO + NH 3 RHC (reduction half-cycle), proposed to occur via two distinct pathways involving adsorbed NH 3 and gas-phase NH 3 . The resulting NO + NH 3 RHC model is validated using spatiotemporal N 2 measurements covering a wide range of temperatures (200–450 °C) and space velocities (53,000–640,000 h –1 ). N 2 O formation is observed and modeled during NO + NH 3 RHC, with quantitative validation under standard selective catalytic reduction (SCR) conditions. Experimentally measured enthalpic and entropic changes associated with O 2 adsorption on NH 3 -solvated Cu I (ZCu(NH 3 ) 2 ) complexes [ Kamasamudram, K. Catal. Today 2010 , 151 (3–4), 212-222], along with activation energies estimated computationally for the intercage diffusion of ZCu(NH 3 ) 2 complexes [ Paolucci, C. Science 2017 , 357 (6 354), 898-903], are incorporated into a mean field kinetic model for the low-temperature oxidation half-cycle (OHC). Significant NH 3 release is observed during the isothermal oxidation of Cu I sites, attributed to desorption of NH 3 ligands from NH 3 -solvated Cu II dimers (Z 2 Cu 2 (NH 3 ) 4 O 2 ). Reduction of these dimeric complexes leads to the consumption of one NO/Cu II , contradicting the expected reduction stoichiometry. Inclusion of a global Arrhenius rate for the NO titration of Z 2 Cu 2 (NH 3 ) 4 O 2 complexes provides accurate representations of standard SCR on reduced and oxidized catalysts, predicting transient NO and NH 3 consumption between 150 and 250 °C as a function of hydrothermal aging. Deactivation of low-temperature standard SCR by NH 3 is observed at high NH 3 pressures, modeled via the formation of superoxo amino (ZCu(NH 3 ) 3 OO*) complexes during NH 3 titration of Z 2 Cu 2 (NH 3 ) 4 O 2 complexes [ Negri, C. J. Am. Chem. Soc. 2020 , 142 (37), 15884-15896]. The redox kinetic model presented here provides a foundational description of active site redox during low-temperature standard SCR, combining the recent kinetic, spectroscopic, and computational findings on the mechanism of standard SCR over Cu-SSZ-13.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Metal–Ligand Bifunctional Catalysis: The “Accepted” Mechanism, the Issue of Concertedness, and the Function of the Ligand in Catalytic Cycles Involving Hydrogen Atoms

For years, following the ideas of Shvo and Noyori, the core assumption of metal–ligand bifunctional molecular catalysis has relied on the direct involvement of the chelating ligand in the catalytic reaction via a reversible proton (H + ) transfer through cleavage/formation of one of its X–H bonds (X = O, N, C). A recently revised mechanism of the Noyori asymmetric hydrogenation reaction (Dub, P. A. et al. J. Am. Chem. Soc. 2014, 136, 3505) suggests that the ligand is rather involved in the catalytic reaction via the stabilization of determining transition states through N–H···O hydrogen-bonding interactions (HBIs) and not via a reversible H + transfer, behaving in a chemically intact manner within the productive cycle or predominantly in a chemically intact manner within productive cycles. By reexamining selected examples of computational mechanistic studies involving bifunctional catalysts from the literature in the years between 2012–2017, the purpose of this paper is to point out common misconceptions in modeling concerted reactions and show that the actual stepwise nature of key transition states unveils a more complicated catalytic reaction pool (all conceivable catalytic pathways and their crossovers). Such a realization can not only potentially result in a reconsideration of the “accepted” mechanism but also lead us to a new conceptual understanding of the role that the ligand plays in the reaction. Finally, the ultimate goal of this paper is, therefore, to encourage the reader to reconsider the function of the ligand in catalytic cycles of hydrogenation/dehydrogenation with bifunctional catalysts, which until recently has relied almost exclusively on a chemically noninnocent ligand.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Mechanism of Hydrocarbon Functionalization by an Iodate/Chloride System: The Role of Ester Protection

Mixtures of chloride and iodate salts for light alkane oxidation achieve > 20% yield of methyl trifluoroacetate (TFA) from methane with > 85% selectivity (J. Am. Chem. Soc. 2014, 136, 8393-8401). The mechanism of this C–H oxygenation has been probed by examining adamantane as a model substrate. These recent results lend support to the involvement of free radicals. Comparative studies between radical chlorination and iodate/chloride functionalization of adamantane afford statistically identical 3°:2° selectivities (~5.2:1) and kinetic isotope effects for C–H/C–D functionalization {kH/kD = 1.52(3) and 1.6(3)}. Alkane functionalization by iodate/chloride in HTFA is proposed to occur through H-atom abstraction by free radical species including Cl· to give alkyl radicals. Iodine, which forms by in situ reduction of iodate, traps the alkyl radicals as alkyl radicals that are subsequently converted to alkyl esters in HTFA solvent. Importantly, the alkyl ester products (RTFA) are quite stable to further oxidation under the oxidizing conditions due to the protecting nature of the ester moiety.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Nanoionics Drastically Accelerating Mass Transfer at Elevated Temperatures over 750 °C

Nanoionics were previously considered thermally unstable and infeasible for devices operating above 500 °C. Here, we elucidate the design principle for establishing stable nanoionics from various oxides. We utilized reversible solid oxide cells (SOCs) as the test bed and implemented nanoionics using atomic layer deposition (ALD). We demonstrate a straightforward, interface-controlled, practical approach to render a conformal, ∼15 nm thick ALD film, which initially thermodynamically favors the formation of a solid solution with the substrate into surface nanoionics with single or double layers of nanograins with random crystal orientations. The nanoionics exhibited conductivity estimated to be 7 orders of magnitude higher than that of their bulk-scale counterpart. They demonstrated conformability with uniform grain sizes of ∼15 nm, even after electrochemical operation for ∼500 h at 750 °C and 1000 h at 850 °C. The thermal stability and conductivity of such nanoionics represent a conceptual and technological framework in nanoionics.

atomic layer deposition↗
DOE OSTI2022

What Is the Right Level of Activation of a High-Spin {FeNO} 7 Complex to Enable Direct N–N Coupling? Mechanistic Insight into Flavodiiron NO Reductases

Flavodiiron nitric oxide reductases (FNORs), found in pathogenic bacteria, are capable of reducing nitric oxide (NO) to nitrous oxide (N 2 O) to detoxify NO released by the human immune system. Previously, we reported the first FNOR model system that mediates direct NO reduction (Dong, H. T.; et al. J. Am. Chem. Soc. 2018, 140, 13429-13440), but no intermediate of the reaction could be characterized. Here, we present a new set of model complexes that, depending on the ligand substitution, can either mediate direct NO reduction or stabilize a highly activated high-spin (hs) {FeNO} 7 complex, the first intermediate of the reaction. The precursors, [{Fe II (MPA-(RPhO) 2 )} 2 ] (1, R = H and 2, R = t Bu, Me), were prepared first and fully characterized. Complex 1 (without steric protection) directly reduces NO to N 2 O almost quantitatively, which constitutes only the second example of this reaction in model systems. Contrarily, the reaction of sterically protected 2 with NO forms the stable mononitrosyl complex 3, which shows one of the lowest N-O stretching frequencies (1689 cm -1 ) observed so far for a mononuclear hs-{FeNO} 7 complex. Here this study confirms that an N-O stretch & LE;1700 cm -1 represents the appropriate level of activation of the FeNO unit to enable direct NO reduction. The higher activation level of these hs-{FeNO} 7 complexes required for NO reduction compared to those formed in FNORs emphasizes the importance of hydrogen bonding residues in the active sites of FNORs to activate the bound NO ligands for direct N-N coupling and N2O formation. The implications of these results for FNORs are further discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Increased Crystal Field Drives Intermediate Coupling and Minimizes Decoherence in Tetravalent Praseodymium Qubits

Crystal field (CF) control of rare-earth (RE) ions has been employed to minimize decoherence in qubits and to enhance the effective barrier of single-molecule magnets. The CF approach has been focused on the effects of symmetry on dynamic magnetic properties. Herein, the magnitude of the CF is increased via control of the RE oxidation state. The enhanced 4f metal-ligand covalency in Pr 4+ gives rise to CF energy scales that compete with the spin-orbit coupling of Pr 4+ and thereby shifts the paradigm from the ionic ζ SOC >> V CF limit, used to describe trivalent RE-ion, to an intermediate coupling (IC) regime. We examine Pr 4+ -doped perovskite oxide lattices (BaSnO 3 and BaZrO 3 ). These systems are defined by IC which quenches orbital angular momentum. Therefore, the single-ion spin-orbit coupled states in Pr 4+ can be chemically tuned. We demonstrate a relatively large hyperfine interaction of A iso = 1800 MHz for Pr 4+ , coherent manipulation of the spin with Q M = 2Ω R $T$ m reaching up to ~400 for 0.1Pr:BSO at $T$ = 5 K, and significant improvement of the temperature at which $T$ m is limited by $T$ 1 ($T$* = 60 K) compared to other RE ion qubits.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Mechanistic Insight into Tunable Spin Relaxation in Two-Dimensional Type-II Ligand-Perovskite Heterostructures

Two-dimensional (2D) metal-halide perovskites with spin-dependent optical properties hold great promise for spintronic and quantum applications. However, their spin lifetimes, especially for n = 1 2D perovskites, are typically limited to subpicosecond time scales due to rapid spin relaxation driven by strong spin−orbit coupling (SOC), electron−hole exchange interactions, and phonon-mediated scattering. Here, we demonstrate that type-II ligand-perovskite heterostructures overcome these constraints by reducing electron−hole wave function overlap and exciton binding energy. Compared to the type-I 2D perovskite (PEA) 2 PbI 4 with a spin lifetime of 0.29 ps at room temperature, our engineered type-II systems achieve substantially extended spin lifetimes, ∼6.37 ps for (4Tm) 2 PbI 4 and ∼18.47 ps for (4TCNm) 2 PbI 4 . In both materials, spatial charge separation across the perovskite−ligand interface mitigates the Bir−Aronov− Pikus (BAP) mechanism. Temperature- and fluence-dependent measurements reveal Elliott−Yafet (EY)-dominated spin relaxation in (4Tm) 2 PbI 4 , consistent with the observation of coherent phonon oscillation, whereas (4TCNm) 2 PbI 4 exhibits D’yakonov−Perel (DP)-dominated spin relaxation, with weaker phonon coupling further suppressing the EY relaxation, enabling spin lifetimes up to ∼126.81 ps at 5 K. Our findings establish a structural design framework for tailoring spin dynamics in 2D perovskites, offering a promising strategy to engineering spin and optoelectronic properties via rational ligand engineering.

Excitons↗