eV Range Research Articles

Revisited Ti2Nb2O9 as an Anode Material for Advanced Li-Ion Batteries.

Ti2Nb2O9 with a tunnel-type structure is considered as a perspective negative electrode material for Li-ion batteries (LIBs) with theoretical capacity of 252 mAh g-1 corresponding to one-electron reduction/oxidation of Ti and Nb, but only ≈160 mAh g-1 has been observed practically. In this work, highly reversible capacity of 200 mAh g-1 with the average (de)lithiation potential of 1.5 V vs Li/Li+ is achieved for Ti2Nb2O9 with pseudo-2D layered morphology obtained via thermal decomposition of the NH4TiNbO5 intermediate prepared by K+→ H+→ NH4+ cation exchange from KTiNbO5. Using operando synchrotron powder X-ray diffraction (SXPD), single-phase (de)lithiation mechanism with 4.8% unit cell volume change is observed. Operando X-ray absorption near-edge structure (XANES) experiment revealed simultaneous Ti4+/Ti3+ and Nb5+/Nb4+ reduction/oxidation within the whole voltage range. Li+ migration barriers for Ti2Nb2O9 along [010] direction derived from density functional theory (DFT) calculations are within the 0.15-0.4 eV range depending on the Li content that is reflected in excellent C-rate capacity retention. Ti2Nb2O9 synthesized via the ion-exchange route appears as a strong contender to widely commercialized Ti-based negative electrode material Li4Ti5O12 in the next generation of high-performance LIBs.

Fullerite C60 optical constants in the C 1s NEXAFS region

Using data on the absorption cross sections the refraction coefficient spectral dependence n(E) and the spectra of the remaining optical coefficients (reflection coefficient, phase shift, and atomic form factor) in the fullerite C60 C 1s near edge X-ray absorption fine structure (NEXAFS) region (280–350 eV) were determined. For the n(E) calculations the Kramers-Kronig integral relations (KKRs) were used. The KKR computations were performed using data on atomic carbon absorption cross sections in the 10–30000 eV range and on solid and gaseous C60 – in the 0–120 eV. Absorption cross section spectrum in the fullerite C60 C 1s NEXAFS region were measured.

Hydrogen storage on multiple palladium-decorated graphene

The geometries, structural stability, electrical and magnetic characteristics of pure and multiple palladium (Pd)-adsorbed graphene, followed by hydrogen adsorption, are investigated using first-principles calculations with the density functional theory. In the DFT-D2 technique, first-principles computations with the van der Waals interaction are done using the generalized gradient approximation. In a [Formula: see text] supercell, the adsorption energy per Pd atom is found to be 1.20 eV in the optimal adsorption shape. The bandgap of 51 meV has opened in multiple Pd-decorated graphene, according to band calculations. This band’s opening is ascribed to a symmetry break. The binding energy for hydrogen adsorption in optimal double Pd-decorated graphene was determined to be in the range of (0.14–0.73) eV per hydrogen molecule, indicating that Pd-decorated graphene might be used as a hydrogen storage material.

(Invited) Defect Microstructural Evolution of Co-Implanted and Gyrotron Microwave-Annealed GaN

The success of the next generation of (Al)GaN-based power devices depends on the ability to form selective-area p-type regions, which can be accomplished by ion implantation of the prevailing acceptor dopant, Mg. Ion implantation induces lattice damage and creates point defects within the material, which evolve in response to activation annealing. Lattice dilation can be reduced and point defects removed or agglomerated into clusters by annealing [1], however sufficiently extreme annealing conditions degrade or decompose GaN [2]. The p-type activation of Mg-implanted GaN can be further aided by co-implantation with N, which is believed to enhance the removal of implant-induced nitrogen vacancies (VN) in the material that act as donors and compensate free holes [3].To restore the bulk crystalline quality, lower the concentration of defects, and activate the implanted dopants without degrading the material, specialized annealing techniques are required either to heat very rapidly [4] and/or use ultra-high pressure conditions [5] in order to obtain high-conductivity p-type material, and activation of Mg-implanted material remains an area of active research.In this study, we report on the micro-structural changes in p-type implanted GaN material after activation-annealing by pulsed gyrotron microwave. MOCVD-grown unintentionally doped (UID) GaN is grown on n+-HVPE GaN, co-implanted with Mg/N to a depth of 250 nm, capped with AlN, and annealed using a gyrotron under an N2 overpressure of 3 MPa. Gyrotron microwave annealing is performed in pulses of 5–8 sec with maximum temperatures between 1350–1450 °C. Detailed optical, structural, and electrical characterization are conducted to better understand the impact on defect microstructure, and to verify p-type conductivity. Mitigation of implant-induced damage to the lattice is further characterized by transmission electron microscopy (TEM) and x-ray diffraction (XRD). We correlate damage removal (by this annealing methodology) with a trend in optical signature through spatially-resolved low-temperature PL. At the optimized anneal condition of 5 pulses at 1450 °C maximum temperature, and 8 s pulse length, the average intensity ratio of the MgGa acceptor-related UVL to the implant-induced donor VN-related GL2 is 6.6 with a standard deviation 66% of the mean across the material, suggesting high and uniform acceptor activation relative to unoptimized beam conditions. We also characterize regions of the sample in which the GL2 luminescence is suppressed and a dominant YL emerges in the 2.2–2.5 eV range, which is attributed to unintentionally introduced CN-ON complexes in GaN grown by MOCVD [5]. For the optimized annealing condition, diode I-V measurements indicate clear p-n diode behavior with threshold voltages between 3.1–3.5 V and Ion/Ioff ratio of up to 106.This work is funded by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy under the PNDIODES programs directed by Dr. Isik Kizilyalli.[1] Y. Wang, et al., physica status solidi (b), 257.4, 1900705 (2020)[2] G. Alfieri, et al. J. Appl. Phys., 123, 205303 (2018)[3] R. Tanaka et al. Japan. J. Appl. Phys., 59 , SGGD02 (2020)[4] J. D. Greenlee, et al, ECS J. Solid State Sci Technol., 4(9) (2015)[5] K. Iwata et al, J. Appl. Phys., 127(10) (2020)[6] V. Meyers et al. in review, J. Appl. Phys. (2021) Figure 1

Influence of Tb3+ ions concentration and temperature on lithium bismuth alumino borosilicate glasses for green photonic device applications

Lithium bismuth alumino borosilicate (LiBiAlBSi) glasses doped with various concentrations of trivalent terbium (Tb3+) ions were prepared to explore their physical, optical, and photoluminescence (PL) characteristics features. Diffraction pattern recorded for an undoped as well as doped (1.5 mol% of Tb3+) LiBiAlBSi glass ascertained the amorphous nature. Absorption spectra reveal several peaks in n-UV and blue regions. The indirect optical band gap for Tb3+ doped LiBiAlBSi glasses was found in the 3.16-3.46 eV range. PL measurements such as emission (under 378 nm excitation) and excitation (under 542 nm emission) were recorded to study the usage of the as-prepared glasses for green photonic device applications. PL emission spectra reveal four emission bands of Tb3+ ions originating from the excited level of 5D4 to 7FJ (=3,4,5,6) levels. The intensity of the emission peak observed in the green region at 542 nm (5D4→7F5) escalates up to 1.5 mol% of Tb3+ ion concentration and declines beyond due to concentration quenching. Dexter theory applied to the PL emission spectral features reveals dipole-dipole interaction among Tb3+ ions responsible for the transfer of energy and thereby concentration quenching. The CIE coordinates and CCT values calculated for the as-prepared glasses are closure to the values of intense green emission given by the European Broadcasting Union illuminant. The experimental lifetime values (τexp) measured for the intense green emission (5D4→7F5) are reducing with the upsurge in the content of Tb3+ ions in the titled glasses. Correlation of τexp values with the PL emission spectral data facilitate the estimation of radiative properties. Relatively high activation energy value estimated from the temperature-dependent PL show the thermal stability of the optimized glass. The PL (excitation, emission, decay, temperature-dependent) studies along with colorimetric studies confirm the aptness of the LBiAlBSiTb15 glass for photonic applications such as laser and tricolour w-LEDs as a green emitting component.

Effect of Gd3+ substituted Cadmium silicate nanophosphor for dosimetric applications

The Gd3+ substituted CdSiO3 nanophosphors (1–9 mol %) have been synthesized by using solution combustion (SC) method. Phosphors have been well reported by powder X-ray diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and UV–Visible spectroscopy. PXRD patterns reveal monoclinic CdSiO3 phase which can be obtained for calcining the samples at 800 °C for 2 h and average size of the samples is (22–42) nm as calculated by Scherer's formula and W–H plots. SEM micrographs show that crystallites are of agglomerated and irregular in shape. The band gap was evaluated by Wod and Tauc method is in the range of (5.18–5.35) eV. A fine determined single Thermoluminescence (TL) glow peak at 138 °C was verified for all the UV exposed models. So prepared nanomaterial's can used in nano-radiation dosimeters.

Crystal structure and optical properties of the Bi–Fe–W–O pyrochlore phase synthesized via a hydrothermal method

The present work investigated the influence of the hydrothermal synthesis conditions (hydrothermal fluid pH) on the composition, structural parameters, morphology, and optical properties of nanocrystalline particles based on a phase of variable composition that forms in the Bi2O3–Fe2O3–WO3 system and has the cubic pyrochlore structure A2B2O6O′δ = (Bi, Fe, VA)2(Fe, W)2O6O′δ , where VA are cation vacancies at the A-site (hereinafter BFWO). The BFWO phase structural parameters were refined by the Rietveld method, and the distribution of Fe over the structurally nonequivalent sites was established. It was shown that the fraction of Fe at the A-site out of the total amount of Fe depends on the BFWO chemical composition and can vary from 0 to ~15%. The results of the Mössbauer study showed that Fe atoms are characterized by two states that differ significantly in terms of the nearest environment, but it was found impossible to explain the differences in the state of iron atoms by their simultaneous presence at the sites A and B. According to the X-ray diffraction (XRD) data, the average crystallite size was shown to change depending on the conditions of hydrothermal synthesis. When the values of hydrothermal fluid pH increased, the average crystallite size first increases from ~78 nm at pH 2 up to 181 nm at pH 5, and then decreases to ~133 nm at pH 7. The scanning electron microscopy (SEM) data have shown that crystallites in all samples grow together into aggregates, the shape of which is close to spherical. The average aggregate size depends on the hydrothermal fluid pH in a similar way: when pH increases, the aggregate size first increases from ~330 nm at pH 2 up to 880 nm at pH 5, and then decreases to ~340 nm at pH 7. The band gap (Eg) of the obtained materials for direct allowed electronic transitions was calculated from the diffuse reflectance spectrum data and found to be in the 2.16–2.41 eV range. The Eg value was shown to decrease with the enrichment of the BFWO composition in Bi and Fe and with a decrease in the volume fraction of crystallites that make up the surface layer of aggregates and have a size of about 30–40 nm.

Radiative emission analysis of Sm3+ ions doped borosilicate glasses for visible orange photonic devices

Sm3+ ions doped borosilicate glasses with variable concentration of Sm3+ ions (0.5 to 2.5 mol%) in steps of 0.5 mol% have been synthesized by using melt quench method. The X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR) measurements were done for structure analysis. Broad hump in XRD determine the amorphous nature of the as prepared glass. The absorption spectra observed in UV-vis-NIR range and band gap has been determined to be in 3.011-3.020 eV range for all the prepared glasses. The photoluminescent (PL) excitation reveals 402 nm intense excitation peak and strong emission at around 600 nm as observed from PL spectral measurements. The colorimetric properties were studied to realize the utility of the glasses reported in this article for orange colour photonic device applications. The chromaticity diagram reveals orange emission with 0.594, 0.404 CIE coordinates. The PL decay spectral studies were utilised to acknowledge the type of energy transfer mechanism and illustrated dipole-dipole interaction between Sm3+ ions.

A Statistical Study of Low‐Energy Ion Flux Enhancements by EMIC Waves in the Inner Magnetosphere

AbstractWe have studied the statistical properties of low‐energy proton (H+) and helium (He+) ion flux enhancements associated with electromagnetic ion cyclotron (EMIC) waves in the inner magnetosphere using Van Allen Probes data for 2013–2017. We identified 167 low‐energy ion flux enhancements when the EMIC waves occurred in a He‐band or in a multiple band (H‐band and He‐band) with strong He‐band and weak H‐band wave activity and found that most of them occurred from the noon to the premidnight sector near the magnetic equator just inside the plasmapause. Of 167 flux enhancement events, 68 exhibited only He+ flux enhancements, and 99 exhibited both H+ and He+ flux enhancements. The EMIC wave‐associated flux enhancement events are mostly energized in the direction perpendicular to the background magnetic field. When both H+ and He+ fluxes are simultaneously enhanced, the H+ flux events have a peak energy distributed in the range of 2–100 eV, and the peak energies of the He+ flux events are distributed in the 2–600 eV range, implying that the helium ions are more energized than the protons. The peak energies of only He+ flux enhancement without H+ flux enhancement are mostly distributed in a lower energy range, 2–10 eV. The energization of H+ and He+ ions can be explained by a linear plasma flow associated with EMIC waves. We suggest that the wave‐associated linear plasma motion is a likely mechanism to explain the observations.

Exploring the structural, elastic, optical, dielectric and magnetic characteristics of Ca2+ incorporated superparamagnetic Zn0.5−xCa0.1Co0.4+xFe2O4 (x = 0.0, 0.05 & 0.1) nanoferrites

This work is aimed to understand influence of 10% Ca doping on the structural, optical, dielectric and magnetic behavior of half doped Zinc-Cobalt nanoferrites. Zn0.5−xCa0.1Co0.4+xFe2O4 (x = 0.0, 0.05 & 0.1) nanoferrites with crystallite size in 10–13 nm range were synthesized through a sol-gel auto-incinerated route. Rietveld profile refinement of PXRD patterns, observation of spinel ferrite type fcc Laue rings in SAED patterns, Raman modes (A1g,T2g & Eg) and metal-oxide (υ1 & υ2) bonds in 400–600 cm−1 IR range illustrated formation of single phase mixed valent spinel type fcc nanoferrites. In these nanoferrites Zn2+ ion resides at tetrahedral (TA) site, while Co2+ & Ca2+ ions preferentially fill the octahedral OB site and Fe3+ ion occupy both TA & OB sites. Moderate optical absorbance in blue color region and strong absorbance in the lower UV region is observed in these nanoferrites, which is owing to presence of mixed valent ions at the OB and TA sites respectively. 10% Ca doping in these half doped Zn-Co nanoferrites led to considerable decrement in the band gap energy (Eg) and turning them to semiconducting state (Eg in 2.5–2.3 eV range). In these nanoferrites hopping of electrons between divalent Fe2+, Ca2+, Zn2+, Co2+ & trivalent Fe3+ & Co3+ cations led to systematic decrease in the dielectric parameters with frequency. These nanoferrites exhibited superparamagnetism with a high magnetic moment (~ 2.9–3.0μB/f.u.) at room temperature. Systematic enhancements in saturation magnetization (Ms), coercivity (Hc), remanence (Mr) and squareness ratio at low temperatures revealed changing of superparamagnetic character to soft ferrimagnetic state of these nanoferrites. At 20K, highest value of Ms = 119 emu/g was observed for Zn0.5Ca0.1Co0.4Fe2O4 nanoferrite, while highest Hc = 2911 Oe & Mr = 61.0 emu/g were recorded for Zn0.4Ca0.1Co0.5Fe2O4 nanoferrite. Thus, a moderate 10% Ca2+ ion incorporation in Zn0.5−xCa0.1Co0.4+xFe2O4 (x = 0.0, 0.05 & 0.1) nanoferrites is emerged as an effective route for obtaining superparamagnetic nanoferrites with high magnetic moment and reduced band gap energy. Unique magneto-optical characteristics of Zn0.5−xCa0.1Co0.4+xFe2O4 (x = 0.0, 0.05 & 0.1) nanoferrites would project them as a good material for opto-magnetic, drug carrier, biomedical contrast agent and magnetic storage applications.

Tuning the Electronic Properties of Graphane via Hydroxylation: An Ab Initio Study.

The thermodynamic stability of hydroxylated graphane, that is, fully sp3 graphene derivatives coordinated with −H and −OH groups, has been recently demonstrated by ab initio calculations. Within the density functional theory approach, we investigate the electronic property modifications of graphane by progressive hydroxylation, that is, by progressively substituting −H with −OH groups. When 50% of graphane is hydroxylated, the energy bandgap reaches its largest value of 6.68 eV. The electronic affinity of 0.8 eV for graphane can widely change in the 0.28–1.60 eV range depending on the geometric configuration. Hydroxylated graphane has two interfaces with vacuum, hence its electron affinity can be different on each interface with the formation of an intrinsic dipole perpendicular to the monolayer. We envisage the possibility of using hydroxylated graphane allotropes with tunable electronic affinity to serve as interfacial layers in 2D material-based heterojunctions.

Characterization of Agfa Structurix series D4 and D3sc x-ray films in the 0.7-4.6 keV energy range.

X-ray films remain a key asset for high-resolution x-ray spectral imaging in high-energy-density experiments conducted at the National Ignition Facility (NIF). The soft x-ray Opacity Spectrometer (OpSpec) fielded at the NIF has an elliptically shaped crystal design that measures x rays in the 900-2100eV range and currently uses an image plate as the detecting medium. However, Agfa D4 and D3sc x-ray films' higher spatial resolution provides increased spectral resolution to the data over the IP-TR image plates, driving the desire for regular use of x-ray film as a detecting medium. The calibration of Agfa D4 x-ray film for use in the OpSpec is communicated here. These calibration efforts are vital to the accuracy of the NIF opacity measurements and are conducted in a previously un-studied x-ray energy range under a new film development protocol required by NIF. The absolute response of Agfa D4 x-ray film from 705 to 4620eV has been measured using the Nevada National Security Site Manson x-ray source. A broader range of energies was selected to compare results with previously published data. The measurements were taken using selected anodes, filters, and applied voltages to produce well-defined energy lines.

Calibration of nuclear recoils at the 100 eV scale using neutron capture

The development of low-threshold detectors for the study of coherent elastic neutrino-nucleus scattering and for the search for light dark matter necessitates methods of low-energy calibration. We suggest this can be provided by the nuclear recoils resulting from the γ emission following thermal neutron capture. In particular, several MeV-scale single-γ transitions induce well-defined nuclear recoil peaks in the 100 eV range. Using the FIFRELIN code, complete schemes of γ-cascades for various isotopes can be predicted with high accuracy to determine the continuous background of nuclear recoils below the calibration peaks. We present a comprehensive experimental concept for the calibration of CaWO4 and Ge cryogenic detectors at a research reactor. For CaWO4 the simulations show that two nuclear recoil peaks at 112.5 eV and 160.3 eV should be visible above background simply in the spectrum of the cryogenic detector. Then we discuss how the additional tagging for the associated γ increases the sensitivity of the method and extends its application to a wider energy range and to Ge cryogenic detectors.

Search for a Heavy Neutrino in the Mass Range under 750 keV Using Electron Capture in 7Be

We present a reanalysis of the experimental data of electron capture in $^7$Be embedded in Ta which have been published by other authors. Our goal is to set upper limits on a mixture of electron neutrino with a possible right-handed heavy neutrino in the 150--800 keV mass range. In the published experiment a $^7$Li recoil energy spectrum in the 20--200 eV range was measured. In case of electron capture with emission of a heavy neutrino, the recoil spectrum should be shifted to the lower energies. We search for an additional Gauss-shaped structure with the same energy width as the main K-shell transition peak. For this we digitize the published spectrum curve, find the energy resolution, calculate the moving sum of the events along the spectrum in the energy interval of about 3 sigma of energy resolution. Then we use the statistical error of this sum to exclude at some level the appearance of an additional peak. Finally, we present the upper limits at a 95\% confidence level on electron neutrino -- heavy neutrino mixing element, $U^2$, in the mass matrix. New upper limits are at least one order of magnitude lower than the existing data in 300--800 keV mass range.

Excited States of Bromopyrimidines Probed by VUV Photoabsorption Spectroscopy and Theoretical Calculations.

We report absolute photoabsorption cross sections for gas-phase 2- and 5-bromopyrimidine in the 3.7–10.8 eV energy range, in a joint theoretical and experimental study. The measurements were carried out using high-resolution vacuum ultraviolet synchrotron radiation, with quantum chemical calculations performed through the nuclear ensemble approach in combination with time-dependent density functional theory, along with additional Franck–Condon Herzberg–Teller calculations for the first absorption band (3.7–4.6 eV). The cross sections of both bromopyrimidines are very similar below 7.3 eV, deviating more substantially from each other at higher energies. In the 7.3–9.0 eV range where the maximum cross-section is found, a single and broad band is observed for 5-bromopyrimidine, while more discernible features appear in the case of 2-bromopyrimidine. Several π* ← π transitions account for the most intense bands, while weaker ones are assigned to transitions involving the nitrogen and bromine lone pairs, the antibonding σ*Br orbital, and the lower-lying Rydberg states. A detailed comparison with the available photo-absorption data of bromobenzene is also reported. We have found significant differences regarding the main absorption band, which is more peaked in bromobenzene, becoming broader and shifting to higher energies in both bromopyrimidines. In addition, there is a significant suppression of vibrational structures and of Rydberg states in the pair of isomers, most noticeably for 2-bromopyrimidine.

Role of plasmons in the LISA test-mass charging process

High-energy particles of galactic and solar origin will charge the test-masses on board laser interferometer space antenna (LISA) and other interferometers for gravitational-wave detection in space. The stochastic noise associated with this charging process is estimated to limit the sensitivity of space interferometers at low frequencies. In a previous paper we have reported a detailed study of low-energy electromagnetic processes affecting the LISA test-mass charging. In particular, we have discussed ionization and electron kinetic emission due to electrons and ions, while the role of plasmons in generating low-energy electrons has been deemed as negligible. Recently, the decay of plasmons has been observed to modify the energy distribution of electrons emitted by ions incident on foils of carbon and gold. Our work is consolidated here accordingly. The contribution of plasmon decay will be considered in future Monte Carlo simulations of LISA test-mass charging in the energy range of a few eV in addition to electron quantum diffraction and backscattering.

Effect of thallium (Tl) substitution for indium (In) on ellipsometric characteristics of TlInSe2 single crystals

TlMeSe2 (Me: Tl, In) semiconducting compounds exhibiting chain structure have been attractive ternary materials in various technological devices. In the TlMeSe2 structure, Tl1+ is monovalent while Me3+ is trivalent ions. The present paper reports the results of spectroscopic ellipsometry measurements performed on Tl1+(Tl0.2In0.8)3+Se2 (abbreviated as Tl1.2In0.8Se2) single crystals which were grown by substituting thallium for indium. The measurements were performed for orientations of E//c and E丄c (E: electric field and c: optical axis). The analyses of ellipsometry data considering air-sample optical model presented the spectral dependencies of dielectric function, refractive index and extinction coefficient in the 1.2–5.0 eV range. Critical point energies of studied single crystal were obtained by fitting second-energy derivative spectra of dielectric function. The determined energies were compared with those of TlInSe2 to understand the effect of thallium-indium substitution in the compound. The crystal structure and atomic compositions of the constituent elements were also reported throughout the paper.

Inverse spin-Hall effect in GeSn

Due to the long spin lifetime and its optical and electrical properties, GeSn is a promising candidate for the integration of spintronics, photonics, and electronics. Here, we investigate the photoinduced inverse spin-Hall effect in a GeSn alloy with 5% Sn concentration. We generate a spin-polarized electron population at the Γ point of the GeSn conduction band by means of optical orientation, and we detect the inverse spin-Hall effect signal coming from the spin-to-charge conversion in GeSn. We study the dependence of the inverse spin-Hall signal on the kinetic energy of the spin-polarized carriers by varying the energy of the impinging photons in the 0.5–1.5 eV range. We rationalize the experimental data within a diffusion model which explicitly accounts for momentum, energy, and spin relaxation of the spin-polarized hot electrons. At high photon energies, when the spin relaxation is mainly driven by phonon scattering, we extract a spin-Hall angle in GeSn which is more than ten times larger than the one of pure Ge. Moreover, the spin–charge interconversion for electrons lying at the Δ valleys of GeSn results to be ≈4.3 times larger than the one for electrons at L valleys.

Heterovalent BiIII/PbII Ionic Substitution in One-Dimensional Trimethylsulfoxonium Halide Pseudo-Perovskites (X = I, Br)

We report on the synthesis and characterization of novel lead and bismuth hybrid (organic–inorganic) iodide and bromide pseudo-perovskites (ABX3) containing the trimethylsulfoxonium cation (CH3)3SO+ (TMSO) in the A site, Pb/Bi in the B site, and Br or I as X anions. All of these compounds are isomorphic and crystallize in the orthorhombic Pnma space group. Lead-based pseudo-perovskites consist of one-dimensional (1D) chains of face-sharing [PbX6] octahedra, while in the bismuth-based ones, the chains of [BiX6] are interrupted, with one vacancy every third site, leading to a zero-dimensional (0D) local structure based on separated [Bi2I9]3– dimers. Five solid solutions for the iodide with different Pb2+/Bi3+ ratios between (TMSO)PbI3 and (TMSO)3Bi2I9, and two for the bromide counterparts, were synthetized. Due to the charge compensation mechanism, these systems are best described by the (TMSO)3Pb3xBi2(1–x)I9 (x = 0.98, 0.92, 0.89, 0.56, and 0.33) and (TMSO)3Pb3xBi2(1–x)Br9 (x = 0.83 and 0.37) formulae. X-ray powder diffraction (XRPD) measurements were employed to determine the crystal structure of all studied species and further used to test the metal cation miscibility within monophasic samples not showing cation segregation. These systems can be described through an ionic defectivity on the pseudo-perovskite B site, where the Pb2+/Bi3+ replacement is compensated by one Pb2+ vacancy for every Bi3+ pair. This leads to a wide range of possible different (numerical and geometrical) chain configurations, leading to the unique features observed in XRPD patterns. The optical band gap of the iodide samples falls in the 2.11–2.74 eV range and decreases upon increasing the Bi3+ content. Interestingly, even a very low loading of Bi3+ (1%) is sufficient to reduce the band gap substantially from 2.74 to 2.25 eV. Periodic density functional theory (DFT) calculations were used to simulate the atomic and electronic structures of our samples, with predicted band gap trends in good agreement with the experimental ones. This work highlights the structural flexibility of such systems and accurately interprets the ionic defectivity of the different pseudo-perovskite structures.

Neutron-Resonance Transmission Analysis with a Compact Deuterium-Tritium Neutron Generator

Neutron Resonance Transmission Analysis (NRTA) is a spectroscopic technique which uses the resonant absorption of neutrons in the epithermal range to infer the isotopic composition of an object. This spectroscopic technique has relevance in many traditional fields of science and nuclear security. NRTA in the past made use of large, expensive accelerator facilities to achieve precise neutron beams, significantly limiting its applicability. In this work we describe a series of NRTA experiments where we use a compact, low-cost deuterium-tritium (DT) neutron generator to produce short neutron beams (2.6~m) along with a $^6$Li-glass neutron detector. The time-of-flight spectral data from five elements -- silver, cadmium, tungsten, indium, and $^{238}$U -- clearly show the corresponding absorption lines in the 1-30 eV range. The experiments show the applicability of NRTA in this simplified configuration, and prove the feasibility of this compact and low-cost approach. This could significantly broaden the applicability of NRTA, and make it practical and applicable in many fields, such as material science, nuclear engineering, and arms control.