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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Multiple Lattice Instabilities and Complex Ground State in Cs 2 Ag Bi Br 6

Metal-halide perovskites (MHPs) are attracting considerable interest for optoelectronic applications, with Cs 2 Ag Bi Br 6 one of the main contenders among lead-free systems. Cs 2 Ag Bi Br 6 crystallizes in a nominally double-perovskite structure, but exhibits a soft lattice with large atomic fluctuations characteristic of MHPs. While crucial to understand electron-phonon and phonon-phonon couplings, the spatiotemporal correlations of these fluctuations remain largely unknown. Here, we reveal these correlations using comprehensive neutron and x-ray scattering measurements on Cs 2 Ag Bi Br 6 single crystals, complemented with first-principles simulations augmented with machine-learned neural-network potentials. We report the discovery of an unexpected complex modulated ground-state structure containing several hundred atoms, arising from a soft-phonon instability of the low-temperature tetragonal phase. Further, our experiments and simulations both reveal extensive correlated two-dimensional fluctuations of Br octahedra at finite temperature, arising from soft optic phonons that are strongly broadened by anhamonicity, reflecting very shallow potential wells. These results provide new insights into the atomic structure and fluctuations in MHPs, critical to understand and control their thermal and optoelectronic properties. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Summary of Analytical Results from Samples Supporting Tank Closure Cesium Removal (TCCR) Batch 3 and Modeling Results for Cs Loading on CST

Savannah River Remediation (SRR) is currently operating the Tank Closure Cesium Removal (TCCR) process to remove 137 Cs from tank waste supernate using an ion exchange process. As part of that process, Savannah River National Laboratory (SRNL) receives and analyzes samples in support of the qualification of each batch to be processed. SRNL recently received supernate samples retrieved from Tank 10H as well as in-tank batch contact samples for characterization in support of qualifying Batch 3 for processing through the TCCR unit. Some results from analysis of those samples have been previously reported. This report documents the remaining analyses of the in-tank batch contact samples as well as the results of ZAM (Zheng, Anthony, Miller) isotherm modeling performed for comparison to the measured results. Results of the additional analyses include analysis of the loading of other radionuclides besides 137 Cs on the crystalline silicotitanate (CST) contained within the in-tank batch contact test samples. Results from those analyses revealed the next highest contributor to the activity on the CST was 90 Sr with an average loading of 2.76E+08 dpm/g CST compared to 3.56E+10 dpm/g CST for the 137Cs. Isotopes of plutonium were also detected on the samples. ZAM modeling was performed using the measured composition of the Tank 10H Batch 3 qualification samples. The modeling predicted a maximum Cs loading approximately 2.2x higher than the measured result. This is a slightly lower ratio (expected/measured) compared to what was observed for the prior TCCR in-tank batch contact testing performed for Batches 1A and 2 where the ZAM results were 2.7-2.8x higher than the measured values.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

Migration of 60 Co, 133 Ba, 137 Cs, and 152 Eu from cementitious wasteforms in field lysimeter experiments

Safe and effective storage of radioactive waste is essential to protect environmental health. Due to the potential for accidental releases and the severity of the associated risks, it is imperative to further understand radionuclide transport should an accident occur. This work analyzed the vadose zone migration of radionuclides from cementitious wasteforms at the Savannah River Site after ten years. The observed radionuclides are prominent constituents of radioactive waste or analogs for other groups or series of radionuclides. Lysimeters were first analyzed in 2016 using a collimated high-purity germanium gamma-ray spectrometer to non-destructively measure the concentration of each radionuclide in the sediment column as a function of depth. Following these measurements, the lysimeters were redeployed in the field for another 4 years. All radionuclides in all lysimeters were observed to transport further during the redeployment period; however, the extent of migration varied with the material used for introduction. Except for 137 Cs, migration through the sediment control system increased with decreasing ionic potential (ionic charge/radius); migration order: 152 Eu< 137 Cs< 60 Co< 133 Ba. Overall, the cementitious wasteforms were observed to decrease radionuclide migration extent relative to the filter paper. In both cementitious wasteforms, the migration extent increased in the order 152 Eu< 133 Ba< 60 Co< 137 Cs. However, less migration was measured when the radionuclides were incorporated into a reducing grout wasteform. The novelty of this paper is the demonstration of a technique capable of creating non-destructive measurements over decade time scales. Ultimately, this work provides insight into the long-term migration of alkali, alkali earth, divalent transition metal, and trivalent actinide element isotopes.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Complex Disorder in Type-I Clathrates: Synthesis and Structural Characterization of A8GaxSn46−x (A = Rb, Cs; 6.9 < x < 7.5)

Exploratory studies in the systems Rb–Ga–Sn and Cs–Ga–Sn yielded the cubic type-I clathrates with refined compositions Rb8GaxSn46−x and Cs8GaxSn46−x (6.9 < x < 7.5). Nearly single-phase materials with good crystallinity were obtained from stoichiometric reactions of the elements. The structures were characterized by means of single-crystal X-ray diffraction methods. Both Rb8GaxSn46−x and Cs8GaxSn46−x represents cases, where a Group 13 element randomly substitutes a Group 14 element in the structure. The extent of Ga/Sn mixing is apparently governed by the drive of the system to achieve an optimal valence electron count, and hence, Rb8GaxSn46−x and Cs8GaxSn46−x (x ≈ 8) can be regarded as Zintl phases. This notion is supported by structure refinements on a multitude of single-crystal X-ray diffraction data, which also confirm that both types of cages in the cubic type-I structure are fully occupied by Rb and Cs atoms. The open-framework, comprised of 46 nodes per formula unit, adapts to the incorporation of nearly eight Ga atoms within the matrix of Sn, whereby small, short-range distortions result. The exact nature of these effects is still unclear, as so far, the structural variations could only be modeled as both positional and occupational disorder at one of three framework sites. Since vacancies in the structures of the binary type-I clathrates A8Sn46−x☐x (A = Rb, Cs; ☐ = missing Sn atom) are also known to cause local distortions, the latter were also synthesized with the same protocols used for the synthesis of A8GaxSn46−x and structurally re-analyzed. The results from the latter studies confirm that homogeneity issues abound, and that the final structures/compositions are an intricate function of the experimental conditions.

36 MATERIALS SCIENCE↗
NASA NTRS1990

CS J = 2 yields 1 emission toward the central region of M82

M82 is an irregular (Type II) galaxy located at a distance of approximately 3.5 Mpc. Its unusual appearance and high luminosity, particularly in the infrared, has led many astronomers to classify it as a starburst galaxy. This interpretation is supported by the observation of a large number of radio continuum sources within the central arcminute of the galaxy. These sources are thought to be associated with supernova remnants. The starburst in the central region of the galaxy is believed to have been triggered by tidal interaction with either M81 or the HI cloud surrounding the M81 group. High angular resolution CO-12 J=1 to 0 maps by Nakai (1984) and Lo et al. (1987) indicate the existence of a 400 to 450 pc rotating ring of molecular material about the central region of M82. Red- and blue-shifted absorption components of the HI and OH lines measured by Weliachew et al. (1984) provided the first evidence for the presence of the ring. Many astronomers, each using a different angular resolution, have compared CO-12 J=1 to 0, J=2 to 1, and J=3 to 2 emission and concluded that a large fraction of the CO emission is optically thin. Additional observations suggest that the molecular material toward the center of M82 is clumpy and dense. Unlike the lower rotational transitions of CO, CS is excited only at relatively high densities, n sub H sub 2 greater than or equal to 10(exp 4) cm(-3). It is in clouds with these densities that stars are expected to form. This makes CS an excellent probe of star formation regions. Researchers observed the CS J=2 to 1 transition (97.981 GHz) toward 52 positions in M82 using the National Radio Astronomy Observatory (NRAO) 12 m telescope.

Walker, C. E.↗
NASA NTRS1991

Cs-135 - Ba-135: A new cosmochronometric constraint on the origin of the Earth and the astrophysical site of the origin of the solar system

It is argued that if Cs-135 was indeed present in the early solar system at the level inferred from evidence presented here, then two major conclusions follow. (1) A supernova contributed newly synthesized r-process matter into the protosolar reservoir within approx. 5 Ma of the Cs/Ba fractionation recorded in LEW 86010; (2) The strong Cs depletion in the bulk Earth reservoir (Cs-133/Ba-135 approx. 0.1) took place very early in solar system history. If this volatile loss was pre-accretionary, then the accretionary chronology of the Earth is not constrained. However, if it is a consequence of accretion, then the very tight time constraint of approx. less than 5 Ma (rel. to LEW 86010) is obtained for accretion of most of the Earth's mass.

Harper, C. L.↗
NASA NTRS1993

CS band intensity and column densities and production rates of 15 comets

An accurate fluorescence efficiency of the CS(0,0) band and the lifetime of CS have been calculated at 1 AU heliocentric distance. Model-independent CS column densities and production rates are determined from derived fluorescent emission rates (g-factors) and lifetimes for 15 comets: Austin (1982g), Borrelly (1980i), Bradfield (1979X), Crommelin (1983n), Encke (1980), Encke (1984), Giacobini-Zinner (1984e), Halley (1982i), IRAS-Araki-Alcock (1983d), Meier (1980q), Panther (1980u), Stephan-Oterma (1980g), Tuttle (1980h), West (1975n), and Wilson (1986l).

Sanzovo, G. C.↗
NASA NTRS1994

CS multitransitional study of density distribution in star-forming regions. 2: The S140 region

The S140 molecular cloud was observed in five transitions of CS with resolutions of 11 to 45 arcsec. The data were analyzed with both the LVG and microturbulent models of radiative transfer to derive the density structure. It was found that the CS emission comes from three components of gas: a spherical component centered on the infrared cluster, an arc component along the ionization front between the S140 H II region and the dense molecular cloud core, and a high-velocity component from the dense part of a molecular outflow. The spherical component contributes most to the CS emission and was analyzed in more detail than the other components. Using a temperature distribution derived from an analysis of the dust emission from S140, we fit a power-law density distribution of n(r) = n(sub i)(r/r(sub i))(exp -alpha) to the spherical component. The best fit was for n(sub i) = 1.4 x 10(exp 6) (density at r(sub i) = 0.026 pc) and alpha = 0.8. The density (n(sub i)) was found to be greater than or equal to the density required to account for the dust emission, depending on the dust opacity laws adopted. The presence of optical emission (Dinerstein, Lester, & Rank 1979) suggests a clumpy structure for the dense gas. Considerations of the virial mass and the lowest amount of column density required to produce dust emission put the volume filling factor (f(sub nu)) of the dense gas at approximately 0.14-0.5. We compared S140 with other regions of star formation where the density structure has been derived from excitation analysis. Source-source variations in density gradients and clumpiness clearly exist, ranging from alpha = 2 and f(sub nu) approximately 1 in B335 to alpha approximately 0, f(sub nu) approximately 0.1 in M17. There is a tendency for more massive star-forming regions to have a flatter density distribution, a more clumpy structure, and a large number of young stars. The implications of this tendency are discussed.

Zhou, Shudong↗
NASA NTRS2001

Tentative Identification of Interstellar CS by UV Absorption in the C-X Transition

Current chemical models of translucent clouds imply that sulfur is depleted with respect to its average abundance in diffuse clouds as determined by Morton (1975 ApJ,197, 85) by factors exceeding 10. Existing gigahertz emission observations yield sizable uncertainties in the column densities to background stars, and attempts to measure column densities of CS in the lines-of-sight to various stars through the absorption in the A-X (0,0) electronic transition near 257.6 nm have been unsuccessful. CS dissociates primarily through discrete absorptions into predissociating states. In analogy with CO the strongest of these is the C-X band found near 140.0 nm. We report the tentative identification of the C-X band of CS in the interstellar spectra of HD 24398 (zeta Per), HD 148184 (chi Oph), and HD 154368. The estimated column densities will be compared to the predictions of prevailing chemical models.

Smith, Andrew↗
NASA NTRS2018

The Origin of Titan's External Oxygen: Further Constraints from ALMA Upper Limits on CS and CH2NH

Titan's atmospheric inventory of oxygen compounds (H2O, CO2, CO) are thought to result from photochemistry acting on externally supplied oxygen species (O+, OH, H2O). These species potentially originate from two main sources: (1) cryogenic plumes from the active moon Enceladus and (2) micrometeoroid ablation. Enceladus is already suspected to be the major O+ source, which is required for CO creation. However, photochemical models also require H2O and OH influx to reproduce observed quantities of CO2 and H2O. Here, we exploit sulphur as a tracer to investigate the oxygen source because it has very different relative abundances in micrometeorites (S/O approx. 10(exp -2) and Enceladus' plumes (S/O approx. 10(exp -5). Photochemical models predict most sulphur is converted to CS in the upper atmosphere, so we use Atacama Large Millimeter/submillimeter Array (ALMA) observations at approx. 340 GHz to search for CS emission. We determined stringent CS 3 sigma stratospheric upper limits of 0.0074 ppb (uniform above 100 km) and 0.0256 ppb (uniform above 200 km). These upper limits are not quite stringent enough to distinguish between Enceladus and micrometeorite sources at the 3 sigma level and a contribution from micrometeorites cannot be ruled out, especially if external flux is toward the lower end of current estimates. Only the high flux micrometeorite source model of Hickson et al. can be rejected at 3 sigma. We determined a 3 sigma stratospheric upper limit for CH2NH of 0.35 ppb, which suggests cosmic rays may have a smaller influence in the lower stratosphere than predicted by some photochemical models. Disk-averaged C3H4 and C2H5CN profiles were determined and are consistent with previous ALMA and Cassini/CIRS measurements.

Teanby, N.A.↗
NASA NTRS2024

Accurate Infrared Line Lists for 20 Isotopologues of CS 2 at Room Temperature

To facilitate atmospheric and spectroscopic studies of carbon disulfide, or CS 2 , in both planetary and exoplanetary atmospheres, we adopt the “Best Theory + Reliable High-resolution Experiment” algorithm to generate semiempirical IR line lists for the 20 most abundant CS 2 isotopologues, denoted as Ames-296K. The IR lists are computed using the Ames-1 potential energy surface, refined using the experimental transition set and an ab initio dipole moment surface fitted from CCSD(T)/aug-cc-pV(T/Q/5+d)Z dipoles extrapolated to a one-particle basis set limit. The IR lists cover the range of 0–10,000 cm -1 , with an S 296K cutoff at 10 -31 cm -1 /molecule·cm -2 (abundance included). A “natural” IR line list at 296 K includes about 10 million lines of the 20 isotopologues, with their intensities scaled by the corresponding abundances. The zero-point energy, partition functions, and abundances are reported for each isotopologue. The energy levels in the global effective Hamiltonian model for 12 C 32 S 2 are adopted to improve the line position accuracy. This new IR list for the main isotopologue is denoted as A+I.296K. Reliable HITRAN2020 line positions are also utilized to improve the accuracy of the 32 S 12 C 34 S, 32 S 12 C 33 S, and 32 S 13 C 32 S isotopologue line lists. The final composite line list is validated against Pacific Northwest National Laboratory experimental cross sections, showing excellent agreement. The agreement supports the quality of the composite line list and the power of synergy between experiment and theory. The new data are proposed for use in updating and expanding the CS 2 data in HITRAN and other high-resolution IR databases. Supplementary files are available in Zenodo and AHED.

Exoplanet atmospheric composition↗
DOE OSTI2026

Online Alpha Monitoring of High Cs-137 Hanford and SRS High Level Waste with Tensioned Metastable Fluid Detectors

The Department of Energy’s Hanford and Savannah River Sites maintain millions of gallons of caustic supernate and salt high activity waste in their high-level waste (HLW) tank farm inventories. The Savannah River Site is currently treating this waste with a calixarene-based solvent extraction of Cs-137 to reduce these inventories. Hanford is employing an at-tank crystalline silico titanate (CST) based solid phase extraction methodology to reduce their liquid HLW inventories. Due to the high solubility of Cs-137 and the relative insolubility of the actinides in these caustic waste forms, the beta to alpha radioactivity ratio can often exceed six orders of magnitude in the feed solutions to these treatment processes. This unique characteristic leads to significant technical challenges in making rapid gross alpha measurements in the presence of the overwhelming beta, gamma, as well as dissolved sodium salt in these HLW matrices. Conventional radioanalytical techniques, such as liquid scintillation analysis or gas flow proportional counting require significant radiochemistry preparation prior to the radiometric measurements for gross alpha activity. These required pretreatments render these technologies untenable for rapid quantification of gross alpha activity that could be required to support on or at-line measurements ensuring a waste stream will meet regulatory requirements. The radiation measurement properties of Tensioned Metastable Fluid Detectors (TMFDs) have been studied by Purdue University’s Taleyarkhan research group for well over a decade. Fluids tensioned to the appropriate degree will rupture when struck by radiation, resulting in a measurable cavitation event. The negative pressure generating this tension can be adjusted by centrifugal rotation or by acoustic means in such a way that these cavitation events can be generated from alpha radiation but will not be generated by beta or gamma radiation. Purdue University and the Savannah River National Laboratory are currently collaborating to develop a gamma/beta blind, spectroscopic alpha measurement system based on the Tensioned Metastable Fluid Detector technology to provide a potential solution for performing rapid gross alpha measurements on these high gamma/beta sample matrices. Measurements using the Indirect Drive Acoustically Tensioned Metastable Fluid Detectors developed as part of this collaboration were performed with an alpha emitting radionuclide. Successful determination of gross alpha activity was observed, indicating a potential pathway for rapid gross alpha measurements in remote-handled shielded cells or in process situations requiring online alpha monitoring. Measurements using this system have been conducted on high beta activity solutions, demonstrating the beta blind capability of this system. Measurements are currently underway to test the system’s capability to measure gross alpha activity on Savannah River Site high level waste high Cs-137 samples that have been measured by the SRNL radiochemistry team. This work was supported by the DOE EM Technology Development program.

DiPrete, David [Savannah River National Laboratory↗
DOE OSTI2020

Materials Data on Cs(MnP)2 by Materials Project

Cs(MnP)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Cs1+ is bonded in a distorted body-centered cubic geometry to eight equivalent P+2.50- atoms. All Cs–P bond lengths are 3.66 Å. Mn2+ is bonded to four equivalent P+2.50- atoms to form a mixture of edge and corner-sharing MnP4 tetrahedra. All Mn–P bond lengths are 2.28 Å. P+2.50- is bonded in a 4-coordinate geometry to four equivalent Cs1+ and four equivalent Mn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(SbSe2)2 by Materials Project

Cs(SbSe2)2 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. Cs1+ is bonded in a 9-coordinate geometry to nine Se+1.75- atoms. There are a spread of Cs–Se bond distances ranging from 3.67–4.06 Å. There are two inequivalent Sb3+ sites. In the first Sb3+ site, Sb3+ is bonded to five Se+1.75- atoms to form distorted edge-sharing SbSe5 square pyramids. There are a spread of Sb–Se bond distances ranging from 2.59–3.34 Å. In the second Sb3+ site, Sb3+ is bonded in a see-saw-like geometry to four Se+1.75- atoms. There are a spread of Sb–Se bond distances ranging from 2.62–3.11 Å. There are four inequivalent Se+1.75- sites. In the first Se+1.75- site, Se+1.75- is bonded in a distorted rectangular see-saw-like geometry to one Cs1+ and three Sb3+ atoms. In the second Se+1.75- site, Se+1.75- is bonded in a 5-coordinate geometry to two equivalent Cs1+ and three Sb3+ atoms. In the third Se+1.75- site, Se+1.75- is bonded in a 1-coordinate geometry to three equivalent Cs1+, one Sb3+, and one Se+1.75- atom. The Se–Se bond length is 2.41 Å. In the fourth Se+1.75- site, Se+1.75- is bonded in a 2-coordinate geometry to three equivalent Cs1+ and two Sb3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(CoS)2 by Materials Project

Cs(CoS)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Cs1+ is bonded in a body-centered cubic geometry to eight equivalent S2- atoms. All Cs–S bond lengths are 3.55 Å. Co+1.50+ is bonded to four equivalent S2- atoms to form a mixture of corner and edge-sharing CoS4 tetrahedra. All Co–S bond lengths are 2.23 Å. S2- is bonded in a 4-coordinate geometry to four equivalent Cs1+ and four equivalent Co+1.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(WCl3)3 by Materials Project

Cs(WCl3)3 crystallizes in the trigonal P-3 space group. The structure is three-dimensional. Cs1+ is bonded in a 6-coordinate geometry to six equivalent Cl1- atoms. There are three shorter (3.65 Å) and three longer (3.68 Å) Cs–Cl bond lengths. W+2.67+ is bonded to five Cl1- atoms to form corner-sharing WCl5 square pyramids. There are a spread of W–Cl bond distances ranging from 2.41–2.49 Å. There are three inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a 3-coordinate geometry to two equivalent Cs1+ and one W+2.67+ atom. In the second Cl1- site, Cl1- is bonded in a 2-coordinate geometry to two equivalent W+2.67+ atoms. In the third Cl1- site, Cl1- is bonded in a 2-coordinate geometry to two equivalent W+2.67+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(AsRu)2 by Materials Project

Cs(RuAs)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Cs1+ is bonded in a body-centered cubic geometry to eight equivalent As3- atoms. All Cs–As bond lengths are 3.76 Å. Ru+2.50+ is bonded to four equivalent As3- atoms to form a mixture of corner and edge-sharing RuAs4 tetrahedra. All Ru–As bond lengths are 2.44 Å. As3- is bonded in a 8-coordinate geometry to four equivalent Cs1+ and four equivalent Ru+2.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(CoSe)2 by Materials Project

Cs(CoSe)2 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Cs1+ is bonded in a body-centered cubic geometry to eight equivalent Se2- atoms. All Cs–Se bond lengths are 3.64 Å. Co+1.50+ is bonded to four equivalent Se2- atoms to form a mixture of edge and corner-sharing CoSe4 tetrahedra. All Co–Se bond lengths are 2.36 Å. Se2- is bonded in a 8-coordinate geometry to four equivalent Cs1+ and four equivalent Co+1.50+ atoms.

36 MATERIALS SCIENCE↗