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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

High-precision mass measurement of 103 Sn restores smoothness of the mass surface

As a step towards the ultimate goal of a high-precision mass measurement of doubly magic 100 Sn, the mass of 103 Sn was measured at the Low Energy Beam and Ion Trap (LEBIT) located at the Facility for Rare Isotope Beams (FRIB). Utilizing the time-of-flight ion cyclotron resonance technique, a mass uncertainty of 3.7 keV was achieved, an improvement by more than an order of magnitude compared to a recent measurement performed in 2023 at the Cooler Storage Ring (CSRe) in Lanzhou. Although the LEBIT and CSRe mass measurements of 103 Sn are in agreement, they diverge from the experimental mass value reported in the 2016 version of the Atomic Mass Evaluation (AME2016), which was derived from the measured 𝑄 𝛽 + value and the mass of 103 In. In AME2020, this indirectly measured 103 Sn mass was classified as a “seriously irregular mass” and replaced with an extrapolated value, which aligns with the most recent measured values from CSRe and LEBIT. As such, the smoothness of the mass surface is confidently reestablished for 103 Sn. Here, LEBIT's mass measurement of 103 Sn enabled a significant reduction in the mass uncertainties of five parent isotopes which are now dominated by uncertainties in their respective 𝑄 values.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Dipolar Spin Ice Regime Proximate to an All-In-All-Out Néel Ground State in the Dipolar-Octupolar Pyrochlore Ce 2 Sn 2 O 7

The dipolar-octupolar (DO) pyrochlores, R 2 M 2 O 7 ( R = Ce , Sm , Nd ), are key players in the search for realizable novel quantum spin liquid (QSL) states as a large parameter space within the DO pyrochlore phase diagram is theorized to host QSL states of both dipolar and octupolar nature. New single crystals and powders of Ce 2 Sn 2 O 7 , synthesized by hydrothermal techniques, present an opportunity for a new characterization of the exchange parameters in Ce 2 Sn 2 O 7 using the near-neighbor X Y Z model Hamiltonian associated with DO pyrochlores. Utilizing quantum numerical linked cluster expansion fits to heat capacity and magnetic susceptibility measurements, and classical Monte Carlo calculations to the diffuse neutron diffraction of the new hydrothermally grown Ce 2 Sn 2 O 7 samples, we place Ce 2 Sn 2 O 7 ’s ground state within the ordered dipolar all-in-all-out (AIAO) Néel phase, with quantum Monte Carlo calculations showing a transition to long-range order at temperatures below those accessed experimentally. Indeed, our new neutron diffraction measurements on the hydrothermally grown Ce 2 Sn 2 O 7 powders show a broad signal at low scattering wave vectors, reminiscent of a spin ice, in striking contrast from previous powder neutron diffraction on samples grown from solid-state synthesis, which found diffuse scattering at high scattering wave vectors associated with magnetic and suggested an octupolar quantum spin ice state. We conclude that new hydrothermally grown Ce 2 Sn 2 O 7 samples host a finite-temperature proximate dipolar spin ice phase, above the expected transition to AIAO Néel order. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Three-Dimensional Reconstruction of Nb 3 Sn Films by Focused Ion Beam Cross Sectional Microscopy

Niobium has been the material of choice for SRF cavities for several decades due to its formability and superconducting properties. The accelerating gradient of niobium cavities is, however, rapidly approaching a theoretical limit. To achieve higher accelerating gradients a new material is needed that can sustain high fields. Nb 3 Sn is a promising competitor with a higher superconducting transition temperature and a higher critical field than pure niobium. However, Nb 3 Sn is very brittle and cannot be formed readily into a cavity. The main method for creating Nb 3 Sn cavities is to form a Nb 3 Sn film into a niobium surface using a tin vapor-diffusion method. This technique creates a microcrystalline Nb 3 Sn thin film on the inner surface of the cavity. Tin depleted regions are known to form in the film during this process. Previous studies have analyzed these regions using transmission electron microscopy on cross-sectional lamellae prepared by focused ion beam/scanning electron microscope (FIB/SEM). This method does not provide any three-dimensional (3-D) information about the distribution of tin-deficient regions. In this study we employ a focused ion beam tomographic technique to analyze the 3-D structure of the film. Electron dispersive X-ray spectroscopy is used to image the tin concentration of the film in 3-D. Tin-deficient regions are discovered close to the surface of the Nb 3 Sn film.

Viklund, E.↗
DOE OSTI2023

Sn-modified BaTiO 3 thin film with enhanced polarization

Hybrid molecular beam epitaxy (MBE) growth of Sn-modified BaTiO 3 films was realized with varying domain structures and crystal symmetries across the entire composition space. Macroscopic and microscopic structures and the crystal symmetry of these thin films were determined using a combination of optical second harmonic generation (SHG) polarimetry and scanning transmission electron microscopy (STEM). SHG polarimetry revealed a variation in the global crystal symmetry of the films from tetragonal (P4mm) to cubic (PM3¯m) across the composition range, x = 0 to 1 in BaTi 1–x Sn x O 3 (BTSO). STEM imaging shows that the long-range polar order observed when the Sn content is low (x = 0.09) transformed to a short-range polar order as the Sn content increased (x = 0.48). Consistent with atomic displacement measurements from STEM, the largest polarization was obtained at the lowest Sn content of x = 0.09 in Sn-modified BaTiO 3 as determined by SHG. Furthermore, these results agree with recent bulk ceramic reports and further identify this material system as a potential replacement for Pb-containing relaxor-based thin film devices.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Topological Surface and Bulk States in Dirac Semimetal Alpha-Sn Thin Films

Supported by this DOE grant, we made significant advancements in the study and application of topological surface states (TSS) in topological Dirac semimetal (TDS) α-Sn thin films. Our key findings include: (1) the successful growth of TDS α-Sn thin films via sputtering, an industry-friendly technique, on Si and InSb substrates, marking a breakthrough over previous molecular beam epitaxy methods, (2) the demonstration of enhanced damping in adjacent NiFe thin films due to the TSS of α-Sn, (3) the first observation of a strong bilinear magneto-electric resistance (BMER) effect in TDS materials at room temperature, with responses surpassing previous results, (4) the identification of quantum oscillations in α-Sn thin films associated with the TSS, revealing critical quantum transport characteristics such as Berry phase and quantum mobility, (5) the first experimental observation of negative magnetoresistance in α-Sn, and (6) the demonstration of spinorbit torque-driven, field-free magnetization switching in an α-Sn/Ag/CoFeB trilayer, achieving efficiency levels higher than conventional heavy-metal-based structures, highlighting the essential role of TSS in enabling the switching process.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

A Template-based Approach to the Photometric Classification of SN 1991bg-like Supernovae in the SDSS-II Supernova Survey

The use of SNe Ia to measure cosmological parameters has grown significantly over the past two decades. However, there exists a significant diversity in the SN Ia population that is not well understood. Overluminous SN 1991T-like and subluminous SN 1991bg-like objects are two characteristic examples of peculiar SNe. The identification and classification of such objects is an important step in studying what makes them unique from the remaining SN population. With the upcoming Vera C. Rubin Observatory promising on the order of a million new SNe over a 10 year survey, spectroscopic classifications will be possible for only a small subset of observed targets. As such, photometric classification has become an increasingly important concern in preparing for the next generation of astronomical surveys. Using observations from the Sloan Digital Sky Survey II (SDSS-II) SN Survey, we apply here an empirically based classification technique targeted at the identification of SN 1991bg-like SNe in photometric data sets. By performing dedicated fits to photometric data in the rest-frame redder and bluer bandpasses, we classify 16 previously unidentified 91bg-like SNe. Using SDSS-II host galaxy measurements, we find that these SNe are preferentially found in host galaxies with an older average stellar age than the hosts of normal SNe Ia. We also find that these SNe are found at a further physical distance from the center of their host galaxies. We find no statistically significant bias in host galaxy mass or specific star formation rate for these targets.

Astronomy & Astrophysics↗
DOE OSTI2024

Dramatic Rebrightening of the Type-changing Stripped-envelope Supernova SN 2023aew

Abstract Multipeaked supernovae with precursors, dramatic light-curve rebrightenings, and spectral transformation are rare, but are being discovered in increasing numbers by modern night-sky transient surveys like the Zwicky Transient Facility. Here, we present the observations and analysis of SN 2023aew, which showed a dramatic increase in brightness following an initial luminous (−17.4 mag) and long (∼100 days) unusual first peak (possibly precursor). SN 2023aew was classified as a Type IIb supernova during the first peak but changed its type to resemble a stripped-envelope supernova (SESN) after the marked rebrightening. We present comparisons of SN 2023aew’s spectral evolution with SESN subtypes and argue that it is similar to SNe Ibc during its main peak. P-Cygni Balmer lines are present during the first peak, but vanish during the second peak’s photospheric phase, before H α resurfaces again during the nebular phase. The nebular lines ([O i ], [Ca ii ], Mg i ], H α ) exhibit a double-peaked structure that hints toward a clumpy or nonspherical ejecta. We analyze the second peak in the light curve of SN 2023aew and find it to be broader than that of normal SESNe as well as requiring a very high 56 Ni mass to power the peak luminosity. We discuss the possible origins of SN 2023aew including an eruption scenario where a part of the envelope is ejected during the first peak and also powers the second peak of the light curve through interaction of the SN with the circumstellar medium.

Sharma, Yashvi (ORCID:0000000345311745)↗
NASA NTRS1986

The effects of gravity level during directional solidification on the microstructure of hypermonotectic Al-In-Sn alloys

Five hypermonotectic Al-In-Sn compositions were directionally solidified in a Bridgman-type furnace at normal gravity and during aircraft low-gravity maneuvers. The tendency of the Al-30In alloy to form an indium-rich band at the start of unidirectional growth (SUG) made it difficult to study the integration of L sub 2 into the solidification interface. Hypermonotectic compositions closer to monotectic slightly hypermonotectic caused only a partial band on L sub 2 to form at SUG and allowed the study of such variables as gravity, composition, and monotectic dome height on integration of excess L sub 2 into the solid plus L sub 2 interface. It was found that formation of aligned composite structures for the Al-In-Sn system is not only a function of G and R but also of the degree to which the composition varies from monotectic. Most of the aligned fibrous structures formed from hypermonotectic Al-In-Sn had spacings that were of the order of irregular fibrous structures reported for on monotectic Al-In-Sn. The spacings for the large fibers and aligned globules found for ground and low-gravity processed Al-In-18-Sn-22, respectively, were significantly larger than the others measured and were of the order expected for cell spacings under the growth conditions utilized. It was found that the integration into the solidification front of excess L sub 2 in low gravity was a function of the Sn composition of the alloy.

Curreri, P. A.↗
NASA NTRS1991

Premaximum observations of the type Ia SN 1990N

Spectroscopic and photometric observations of SN 1990N were obtained at ultraviolet and optical wavelengths, beginning 14 days before maximum light. The early observations reveal important differences from spectra of SN Ia's around maximum light. Photometry and spectroscopy obtained after maximum show that SN 1990N is a typical SN Ia and that most of the observed differences are due to the early epoch of the observations. The most significant characteristics are (1) the high velocities of Ca and Si up to 22,000 km/s; (2) the presence of Co and Fe 2 weeks before maximum; and (3) the more rapid increase in the UV flux compared to the optical. The most popular models for white dwarf deflagration that have provided the standard interpretation for SN Ia's at maximum light do not reproduce the high velocities of Ca II and Si II lines observed in SN 1990N.

Leibundgut, Bruno↗
NASA NTRS1996

Electrochemical Studies on LaNi(sub 5-x)Sn(sub x) Metal Hydride Alloys

Electrochemical studies were performed on LaNi(sub 5-x)Sn(sub x) with 0(less than or equal to)x(less than or equal to)0.5. We measured the effect of the Sn substituent on the kinetics of charge transfer and diffusion during hydrogen absorption and desorption, and the cyclic lifetimes of LaNi(sub 5-x)Sn(sub x) electrodes in 250 mAh laboratory test cells. We report beneficial effects of making small substitutions of Sn for Ni in LaNi(sub 5) on the performance of metal hydride alloy anode in terms of cyclic lifetime, capacity and kinetics. The optimal concentration of Sn in LaNi(sub 5-x)Sn(sub x) alloys for negative electrodes in alkaline rechargable secondary cells was found to lie in the range 0.25(less than or equal to)x(less than or equal to)0.3.

metal hydride alloys hydrogen absorption↗
NASA NTRS2009

X-Rays from the Explosion Site: Fifteen Years of Light Curves of SN 1993J

We present a comprehensive analysis of the X-ray light curves of SN 1993J in a nearby galaxy M81. This is the only supernova other than SN 1987A, which is so extensively followed in the X-ray bands. Here we report on SN 1993J observations with the Chandra in the year 2005 and 2008, and Swift observations in 2005, 2006 and 2008. We combined these observations with all available archival data of SN 1993J, which includes ROSAT, ASCA, Chandra, and XMM-Newton, observations from 1993 April to 2006 August. In this paper we report the X-ray light curves of SN 1993J, extending up to fifteen years, in the soft (0.3-2.4 keV), hard (2-8 keV) and combined (0.3-8 keV) bands. The hard and soft-band fluxes decline at different rates initially, but after about 5 years they both undergo a t(sup -1) decline. The soft X-rays, which are initially low, start dominating after a few hundred days. We interpret that most of the emission below 8 keV is coming from the reverse shock which is radiative initially for around first 1000-2000 days and then turn into adiabatic shock. Our hydrodynamic simulation also confirms the reverse shock origin of the observed light curves. We also compare the Ha line luminosity of SN 1993J with its X-ray light curve and note that the Ha line luminosity has a fairly high fraction of the X-ray emission, indicating presence of clumps in the emitting plasma.

Chandra, Poonam↗
NASA NTRS2013

An Early and Comprehensive Millimetre and Centimetre Wave and X-Ray Study of SN 2011dh: a Non-Equipartition Blast Wave Expanding into a Massive Stellar Wind

Only a handful of supernovae (SNe) have been studied in multiwavelengths from the radio to X-rays, starting a few days after the explosion. The early detection and classification of the nearby Type IIb SN 2011dh/PTF 11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at one of the youngest phase ever of a core-collapse SN (days 3-12 after the explosion) in the radio, millimetre and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding SN shock wave does not exhibit equipartition (epsilon(sub e)/epsilon(sub B) approx. 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R(exp −2). Within modelling uncertainties we find an average velocity of the fast parts of the ejecta of 15 000 +/- 1800 km/s, contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast wave regime between the previously defined compact and extended SN Type IIb subtypes. Our results highlight the importance of early (approx.1 d) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio epsilon(sub e)/epsilon(sub B).

gamma rays↗
NASA NTRS2017

The Candidate Progenitor of the Type IIn SN 2010jl Is Not an Optically Luminous Star

A blue source in pre-explosion Hubble Space Telescope (HST)/Wide-Field Planetary Camera 2 (WFPC2) images falls within the 5 Sigma astrometric error circle (approx. 0." 24) derived from post-explosion ground-based imaging of SN 2010jl. At the time the ground-based astrometry was published, however, the SN had not faded sufficiently forpost-explosion HST follow-up observations to determine a more precise astrometric solution and/or confirm if the pre-explosion source had disappeared, both of which are necessary to ultimately disentangle the possible progenitor scenarios. Here we present HST/WFC3 imaging of the SN 2010jl field obtained in 2014, 2015, and 2016 when the SN had faded sufficiently to allow for new constraints on the progenitor. The SN, which is still detected in the new images, is offset by 0."061(+/-) 0."008 (15 +/- 2 pc) from the underlying and extended source ofemission that contributes at least partially, if not entirely, to the blue source previously suggested as the candidate progenitor in the WFPC2 data. This point alone rules out the possibility that the blue source in the pre-explosion images is the exploding star, but may instead suggest an association with a young (less than 56 Myr) cluster and still argues for a massive (greater than 30 solar mass) progenitor. We obtain new upper limits on the flux from a single star at the SN position in the pre-explosion WFPC2 and Spitzer/IRAC images that may ultimately be used to constrain the progenitor properties.

Fox, Ori D.↗
DOE OSTI2022

A flexible linear diffusion acceleration to k-eigenvalue neutron transport with SN discontinuous finite element method

In this paper, we derive a flexible linear diffusion acceleration (LDA) for k-eigenvalue neutron transport discretized with discontinuous finite element method (DFEM) and discrete ordinates(SN). This LDA is based on our two pieces of previous works: the flexible non linear diffusion acceleration (NDA) for DFEM-SN and LDA for k-eigenvalue neutron transport using pre-conditioned Jacobian-free Newton-Krylov with self-adjoint angular flux (SAAF), continuous finite element method(CFEM), and SN. We point out the differences between LDA and NDA for DFEM-SN and the difference between DFEM-SN and SAAF-CFEM-SN for LDA. Numerical tests are presented to compare the convergence behaviour of NDA and LDA. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Nb 3 Sn Superconducting Cavities by Bronze Routes for Accelerator Stewardship

This project explored the challenges of making Nb 3 Sn superconducting radio-frequency (SRF) cavities by bronze routes. The SRF research community has prioritized Nb 3 Sn for many reasons, including the possibility to operate linacs for stewardship applications in continuous-wave mode with compact cryogenic systems. Existing Nb 3 Sn approaches use a cavity body made of niobium and apply tin to the polished cavity interior, a starting point that contains the main costs of present niobium cavity technology. Further complexity is then added because a high vacuum and temperature >1100 °C must be used to prevent formation of undesirable Nb-Sn phases, de-gas interstitial contaminants, and maintain the high purity of the Nb body. The project sought a more cost-effective solution for the same performance opportunities by exploiting the Cu-Sn-Nb diffusion reactions used to make Nb 3 Sn superconducting wires for magnets, which can be carried out at ~700 °C and are compatible with much cheaper copper cavity bodies. The project also sought understanding of the materials science and factors that affect superconducting properties. The project has impacted SRF cavity technology by demonstrating feasibility of alternative routes that enable compact, high-power electron accelerators for energy, security, environment, medical, and commercial applications.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

The structure and migration of twin boundaries in tetragonal β -Sn: An application of machine learning based interatomic potentials

Although atomistic simulations have contributed significantly to our understanding of twin boundary structure and migration in metals and alloys with hexagonal close packed (HCP) crystal structures, few direct atomistic studies of twinning have been conducted for other types of low symmetry materials, in large part due to a lack of reliable interatomic potentials. In this work, we examine twin boundary structure and migration in a tetragonal material, β-Sn, comparing high resolution Transmission Electron Microscopy (TEM) images of deformation twins in β-Sn to the results of direct atomistic simulations using multiple interatomic potentials. ML-based potentials developed in this work are found to give results consistent with our experimental data, revealing faceted twin boundary structures formed by the nucleation and motion of twinning disconnections. We use bicrystallographic methods in combination with atomistic simulations to analyze the structure, energy and shear coupled migration of observed twin facets in β-Sn. In analogy to Prismatic-Basal (PB/BP) interfaces in HCP metals, we discover low energy asymmetric Prismatic-A-plane (PA/AP) interfaces important to twin growth in β-Sn. Finally, a Moment Tensor Potential (MTP) and Rapid Artificial Neural Network (RANN) interatomic potential suitable for studying twinning and phase transformations in Sn are made publicly available as part of this work.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sn(BiTe2)2 by Materials Project

SnBi2Te4 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are five inequivalent Sn2+ sites. In the first Sn2+ site, Sn2+ is bonded to six Te2- atoms to form SnTe6 octahedra that share a cornercorner with one SnTe6 octahedra, corners with five BiTe6 octahedra, edges with four SnTe6 octahedra, and edges with eight BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–6°. There are a spread of Sn–Te bond distances ranging from 3.12–3.25 Å. In the second Sn2+ site, Sn2+ is bonded to six Te2- atoms to form SnTe6 octahedra that share a cornercorner with one SnTe6 octahedra, corners with four BiTe6 octahedra, edges with three BiTe6 octahedra, and edges with six SnTe6 octahedra. The corner-sharing octahedra tilt angles range from 6–55°. There are a spread of Sn–Te bond distances ranging from 3.02–3.47 Å. In the third Sn2+ site, Sn2+ is bonded to six Te2- atoms to form SnTe6 octahedra that share a cornercorner with one SnTe6 octahedra, corners with five BiTe6 octahedra, edges with six SnTe6 octahedra, and edges with six BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–8°. There are a spread of Sn–Te bond distances ranging from 3.14–3.24 Å. In the fourth Sn2+ site, Sn2+ is bonded to six Te2- atoms to form SnTe6 octahedra that share a cornercorner with one SnTe6 octahedra, corners with two equivalent BiTe6 octahedra, edges with four SnTe6 octahedra, edges with four BiTe6 octahedra, and a faceface with one BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 8–48°. There are a spread of Sn–Te bond distances ranging from 3.05–3.41 Å. In the fifth Sn2+ site, Sn2+ is bonded to six Te2- atoms to form SnTe6 octahedra that share corners with five BiTe6 octahedra, edges with two equivalent SnTe6 octahedra, edges with five BiTe6 octahedra, and a faceface with one BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 3–48°. There are a spread of Sn–Te bond distances ranging from 3.14–3.27 Å. There are ten inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share corners with five BiTe6 octahedra, edges with two equivalent SnTe6 octahedra, and edges with five BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–50°. There are a spread of Bi–Te bond distances ranging from 3.03–3.39 Å. In the second Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share a cornercorner with one SnTe6 octahedra, corners with two equivalent BiTe6 octahedra, edges with two equivalent SnTe6 octahedra, and edges with six BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–49°. There are a spread of Bi–Te bond distances ranging from 3.17–3.20 Å. In the third Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share corners with two equivalent SnTe6 octahedra, an edgeedge with one SnTe6 octahedra, and edges with eight BiTe6 octahedra. The corner-sharing octahedral tilt angles are 3°. There are a spread of Bi–Te bond distances ranging from 3.10–3.28 Å. In the fourth Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share a cornercorner with one SnTe6 octahedra, corners with two equivalent BiTe6 octahedra, edges with two equivalent SnTe6 octahedra, and edges with seven BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 5–6°. There are a spread of Bi–Te bond distances ranging from 2.98–3.42 Å. In the fifth Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share a cornercorner with one SnTe6 octahedra, corners with five BiTe6 octahedra, edges with two equivalent SnTe6 octahedra, and edges with eight BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–7°. There are a spread of Bi–Te bond distances ranging from 3.00–3.29 Å. In the sixth Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share a cornercorner with one BiTe6 octahedra, corners with two equivalent SnTe6 octahedra, edges with four BiTe6 octahedra, and edges with five SnTe6 octahedra. The corner-sharing octahedra tilt angles range from 5–6°. There are a spread of Bi–Te bond distances ranging from 3.01–3.40 Å. In the seventh Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share a cornercorner with one BiTe6 octahedra, corners with two equivalent SnTe6 octahedra, edges with three SnTe6 octahedra, and edges with six BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–4°. There are a spread of Bi–Te bond distances ranging from 3.05–3.36 Å. In the eighth Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share corners with two equivalent SnTe6 octahedra, corners with two equivalent BiTe6 octahedra, edges with three SnTe6 octahedra, and edges with six BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–47°. There are a spread of Bi–Te bond distances ranging from 3.13–3.22 Å. In the ninth Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share corners with six SnTe6 octahedra, corners with six BiTe6 octahedra, edges with two equivalent BiTe6 octahedra, and faces with two SnTe6 octahedra. The corner-sharing octahedra tilt angles range from 47–55°. There are a spread of Bi–Te bond distances ranging from 3.08–3.29 Å. In the tenth Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share corners with two BiTe6 octahedra, corners with four SnTe6 octahedra, edges with four BiTe6 octahedra, and edges with six SnTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–13°. There are a spread of Bi–Te bond distances ranging from 3.10–3.32 Å. There are twenty inequivalent Te2- sites. In the first Te2- site, Te2- is bonded in a distorted rectangular see-saw-like geometry to one Sn2+ and three Bi3+ atoms. In the second Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to one Sn2+ and three Bi3+ atoms. In the third Te2- site, Te2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the fourth Te2- site, Te2- is bonded to one Sn2+ and five Bi3+ atoms to form TeSnBi5 octahedra that share a cornercorner with one TeSn4Bi2 octahedra, corners with two equivalent TeBi5 square pyramids, edges with six TeSnBi5 octahedra, and an edgeedge with one TeBi5 square pyramid. The corner-sharing octahedral tilt angles are 1°. In the fifth Te2- site, Te2- is bonded to five Bi3+ atoms to form TeBi5 square pyramids that share corners with two equivalent TeSnBi5 octahedra, edges with three TeSnBi5 octahedra, and edges with two equivalent TeBi5 square pyramids. The corner-sharing octahedral tilt angles are 4°. In the sixth Te2- site, Te2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the seventh Te2- site, Te2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the eighth Te2- site, Te2- is bonded to three Sn2+ and three Bi3+ atoms to form TeSn3Bi3 octahedra that share corners with three TeSn4Bi2 octahedra and edges with nine TeSnBi5 octahedra. The corner-sharing octahedra tilt angles range from 2–3°. In the ninth Te2- site, Te2- is bonded to two equivalent Sn2+ and four Bi3+ atoms to form TeSn2Bi4 octahedra that share corners with two equivalent TeSn3Bi3 octahedra, edges with seven TeSnBi5 octahedra, and edges with two equivalent TeBi5 square pyramids. The corner-sharing octahedral tilt angles are 3°. In the tenth Te2- site, Te2- is bonded in a 3-coordinate geometry to two equivalent Sn2+ and one Bi3+ atom. In the eleventh Te2- site, Te2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the twelfth Te2- site, Te2- is bonded to two equivalent Sn2+ and four Bi3+ atoms to form TeSn2Bi4 octahedra that share corners with two equivalent TeSn4Bi2 octahedra, edges with seven TeSn3Bi3 octahedra, and edges with two equivalent TeSn2Bi3 square pyramids. The corner-sharing octahedral tilt angles are 2°. In the thirteenth Te2- site, Te2- is bonded to four Sn2+ and two equivalent Bi3+ atoms to form TeSn4Bi2 octahedra that share corners with three TeSnBi5 octahedra and edges with nine TeSn3Bi3 octahedra. The corner-sharing octahedra tilt angles range from 1–2°. In the fourteenth Te2- site, Te2- is bonded in a 5-coordinate geometry to three Sn2+ and two equivalent Bi3+ atoms. In the fifteenth Te2- site, Te2- is bonded in a 3-coordinate geometry to three Bi3+ atoms. In the sixteenth Te2- site, Te2- is bonded to two equivalent Sn2+ and three Bi3+ atoms to form TeSn2Bi3 square pyramids that share corners with two equivalent TeSn4Bi2 octahedra, edges with three TeSn2Bi4 octahedra, and edges with two equivalent TeSn2Bi3 square pyramids. The corner-sharing octahedral tilt angles are 5°. In the seventeenth Te2- site, Te2- is bonded to four Sn2+ and two equivalent Bi3+ atoms to form TeSn4Bi2 octahedra that share a cornercorner with one TeSn3Bi3 octahedra, corners with two equivalent TeSn2Bi3 square pyramids, edges with six TeSn2Bi4 octahedra, and an edgeedge with one TeSn2Bi3 square pyramid. The corner-sharing octahedral tilt angles are 2°. In the eighteenth Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to one Sn2+ and three Bi3+ atoms. In the nineteenth Te2- site, Te2- is bonded in a distorted rectangular see-saw-like geometry to two equivalent Sn2+ and two Bi3+ atoms. In the twentieth Te2- site, Te2- is bonded in a 5-coordinate geometry to two equivalent Sn2+ and three Bi3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Enhancing Photostability of Sn-Pb Perovskite Solar Cells by an Alkylammonium Pseudo-Halogen Additive

High-performance tin-lead perovskite solar cells (PSCs) are needed for all-perovskite-tandem solar cells. However, iodide related fast photodegradation severely limits the operational stability of Sn-Pb perovskites despite the demonstrated high efficiency and thermal stability. Herein, this work employs an alkylammonium pseudo-halogen additive to enhance the power conversion efficiency (PCE) and photostability of methylammonium (MA)-free, Sn-Pb PSCs. Density functional theory (DFT) calculations reveal that the pseudo-halogen tetrafluoroborate (BF 4 - ) has strong binding capacity with metal ions (Sn 2+ /Pb 2+ ) in the Sn-Pb perovskite lattice, which lowers iodine vacancy formation. Upon combining BF 4 - with an octylammonium (OA + ) cation, the PCE of the device with a built-in light-scattering layer is boosted to 23.7%, which represents a new record for Sn-Pb PSCs. The improved efficiency benefits from the suppressed defect density. Under continuous 1 sun illumination, the OABF 4 embodied PSCs show slower generation of interstitial iodides and iodine, which greatly improves the device photostability under open-circuit condition. Moreover, the device based on OABF 4 retains 88% of the initial PCE for 1000 h under the maximum-power-point tracking (MPPT) without cooling.

14 SOLAR ENERGY↗