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At least 253 records · Page 14

Remote Radiation Sensing Using Aerial and Ground Platforms

Remote sensing of ionizing radiation has a significant role in waste management, nuclear material management and nonproliferation, and radiation safety. Robotic platforms can surpass the number of tasks that are achieved by humans. With this technique, the operator's radiation exposure can be decreased. Remote sensing allows for the evaluation and monitoring of radiological contamination. Gamma-ray and neutron sensors were integrated onto the robotic platforms. This approach allows for the radiation sensor data to be dynamically tracked and mapped thus enabling further analysis of the radiation flux in temporal and spatial domains. The goal is to complete scheduled tasks while the robot is being irradiated. To achieve this, electronic components must be shielded and radiation hardened. CZT Detector: Cadmium Zinc Telluride (CZT) detector technology has been a promising solution for gamma-ray and x-ray measurements. Detector data is transferred to the Odroid minicomputer that controls and powers the module via the USB. Robot Operating System (ROS) was utilized for data acquisition and data fusion. The Mariscotti method was employed for the spectrum analysis. A function was programmed in ROS for the automatic identification of photopeaks. CLYC Detector: A Cs{sub 2}LiYCl{sub 6}:Ce{sup 3+} (CLYC) detector was used for simultaneous medium-resolution gamma-ray measurements and neutron counting. A 2.54 cm diameter photomultiplier tube (PMT) was equipped with a high voltage supply and a miniature digitizer. Gamma-ray excitation: fast core-to-valence luminescence (CVL) with 1 ns decay constant, and prompt Ce{sup 3+} emission with 50 ns decay constant. Neutron excitation: slow cerium self-trapped excitation (Ce{sup 3+} STE), 1000 ns decay constant. Radiation Source Localization: Maximum Likelihood Estimation (MLE) and gradient-based methods were used to locate the position of a radiation source based on measured radiation intensities. Multi-Particle Transport Code FLUKA: Estimation of radiation damage of the electronic components is important in order to optimize the robot's operational time while it is irradiated. Displacement per atom (DPA) represents the radiation damage in materials exposed to the ionizing radiation. Various shielding layers of different thickness t were analyzed (< 5% statistical error). The model of the controller of the UAS was designed in FLUKA. Conclusion: CZT and CLYC detectors were integrated onto the robotic platforms. Radiation source localization and contour mapping using robotic platforms were studied. Functions for data analysis and fusion were developed in ROS. FLUKA code was utilized to analyze DPA values. Layers of low-density and high-density materials were used to shield the UAS electronics.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Structural and Spectroscopic Characterization of Plutonium and Other Tetravalent Metals Complexed to a Keggin Ion

Here, we report the isolation of the first plutonium(IV) complex with a Keggin ion chelator: Cs 20 [Pu(PW 11 O 39 ) 2 ] 2 ·13H 2 O. Single crystal XRD and solid-state UV–vis absorbance analysis demonstrate the stabilization of Pu 4+ by the Keggin ligand. The unit cell contains two [Pu(PW 11 O 39 ) 2 ] 10– complexes (Pu(PW 11 ) 2 ) bridged by Cs + . Raman and 31 P NMR spectra of Pu(PW 11 ) 2 are consistent with the analogous Zr 4+ , Hf 4+ , Ce 4+ , and Th 4+ complexes. The Pu–O bond distances at the two Pu sites are 2.35(3) and 2.34(3) Å, matching the value extrapolated from the bonding trend built with the other 8-coordinated tetravalent cations. However, the long-range arrangement of the Pu(PW 11 ) 2 complexes within the lattice is unique in the series of M IV (PW 11 ) 2 compounds: pairs of Pu(PW 11 ) 2 are organized perpendicular to each other. Based on solution-state UV–visible absorbance, small-angle X-ray scattering (SAXS), and 31 P NMR, the tetravalent cations quantitatively form the 1:2 species in solution ([Pu(PW 11 O 39 ) 2 ] 10– (aq) ) and no 1:1 species ([Pu(PW 11 O 39 )(H 2 O) x ] 3– (aq) ). Finally, a linear correlation exists between the metal–oxygen distances in the M IV (PW 11 ) 2 compounds and the corresponding metal dioxides, allowing for extrapolation for Pa 4+ , Am 4+ , and Bk 4+ . The results indicate that our microscale POM approach represents a viable pathway to probe properties of rare actinide ions in discrete molecules, beyond the traditional oxide extended solids.

and nuclear chemistry↗

Low-temperature liquid-phase formation of environmentally stable copper halide nanocrystal superlattices and their application to anticounterfeiting patterns

Nanocrystal superlattices have the potential to create a new class of semiconductor materials by combining the photophysical properties of individual nanocrystals with bulk-like structure performance. However, the principles underlying the direct formation of superlattices in liquid phase have not been thoroughly investigated, particularly, those consisting of exciton self-trapping metal halides. Here, in this work, we explore the formation of Cs 3 Cu 2 Br 5 nanocrystal superlattices via liquid-phase crystallization of growing nanocrystals over a reaction period of only a few seconds. Importantly, the reaction temperature and the precursor concentration were found to be key parameters governing the concomitant nanocrystal growth and superlattice formation. The resulting Cs 3 Cu 2 Br 5 superlattices had a well-defined face-centered cubic structure and emitted a single-band bright blue emission when exposed to 280 nm light. Owing to their advantages, such as low toxicity, reabsorption-free, narrow absorption, strong emission, and high environmental stability, the Cs 3 Cu 2 Br 5 superlattices were applicable to anti-counterfeiting applications. Our findings shed light on the liquid-phase assembly of nanocrystals into superlattices and highlight the potential applications of the superlattices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Improved lifetime of a high spin polarization superlattice photocathode

Negative Electron Affinity (NEA) activated surfaces are required to extract highly spin-polarized electron beams from GaAs-based photocathodes, but they suffer extreme sensitivity to poor vacuum conditions that results in rapid degradation of quantum efficiency. We report on a series of unconventional NEA activations on surfaces of bulk GaAs with Cs, Sb, and O 2 using different methods of oxygen exposure for optimizing photocathode performance. Additionally, one order of magnitude improvement in lifetime with respect to the standard Cs–O 2 activation is achieved without significant loss of electron spin polarization and quantum efficiency by codepositing Cs, Sb, and O 2 . A strained GaAs/GaAsP superlattice sample activated with the codeposition method demonstrated similar enhancement in lifetime near the photoemission threshold while maintaining 90% spin polarization.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Roles of Alkali Metals and Ionic Networks in Directing the Formation of Anionic Metal–Organic Frameworks

Integrating different types of fundamental chemical interactions to direct the self-assembly processes and to control the dimension of the network formed by each type of interactions is a promising strategy to develop advanced functional materials. Here, the ionic interaction of alkali metals (Na, K, Cs) towards multi-functional 2,2’-disulfo-4,4’-oxydibenzoic acid is utilized in two solvent systems, aqueous-amide and uro-amide, to synthesize six novel anionic framework materials with dramatically different features and dimensionalities: (Na 3 [Zn 4 O(L 4- ) 3 (e-murea)(H 2 O) 3 ](H 2 N(CH 3 ) 2 +) 3 (CPM-s1), [Zn 4 O(L 4- ) 3 (DMF)]((NH 2 (CH 3 ) 2 +) 6 ) (CPM-s2), Na 6 [(Zn 2 OH 2 ) 3 (L 3- ) 6 ](H 2 O) 3 (CPM-s3), K 3 [Zn 2 (L 4- ) 2 ](H 2 N(CH 3 ) 2 +)(e-murea) 2 (H 2 O) 3 (CPM-s4), K 4 [Zn(L 3- ) 2 ](H 2 O) 2 (CPM-s5), and Cs 6 [Zn(L 4- ) 2 ](H 2 O) 2 (CPM-s6), L 4- = 2,2’-disulfo-4,4’-oxydibenzoate, DMF = N,N-dimethylformamide, e-murea = 1,3-dimethyl-1-2-imidazolidinone). In CPM-s1 to CPM-s6, the alkali-sulfonate ionic bonding networks transformed from 0D clusters with Na + to 1D chains and 2D sheets with K + , and 3D network with Cs + . These vastly differing ionic domains influenced the coordination modes and spatial arrangements of the metal-carboxylate linkers, which consequently, directed the dimensionality of the coordination networks from 3D with Na + to 1D with Cs + . CPM-s1 and CPM-s2, made from tetrameric Zn 4 O clusters are rare examples of anionic MOF-5-type structures. CPM-s3 features an unprecedented hexameric Zn 6 cluster. Even though a large portion of the charge-balancing cations in these materials would hamper hydrogen bonding networks, some of them still exhibit very high ionic conductivity (e.g. 1.25 x 10 -3 S cm -1 in CPM-s3), suggesting the potential of these materials as solid-state electrolytes.

36 MATERIALS SCIENCE↗

In-situ to ex-situ in-plane structure evolution of stern layers on Pt(111) surface: Surface X-ray scattering studies

Here, in-situ to ex-situ evolution of the Cs + in-plane structure in electrochemical Stern layers are investigated on Pt(111) surface with surface X-ray scattering studies. The Cs + single-sublattice (2 x 2) structure of the Stern layer formed in situ in 0.1 M CsF electrolyte evolves eventually to the two-sublattice (2 x 2) structure upon emersion from the electrolyte. While the Cs+ layers maintain the (2 x 2) symmetry, the ex situ layer increases the density progressively over several minutes by incorporating Cs + ions of the electrolyte during the emersion process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Rare Earth Nitrate Hybrid Double Perovskites [Me 4 N] 2 [MLn(NO 3 ) 6 ] (M = Na–Cs; Ln = La–Gd, ex. Pm)

An exploration of the synthetic and structural phase space of rare earth hybrid double perovskites A 2 B'BX 6 (A = organocation, B' = M + , B = M 3+ , X = molecular bridging anion) that include X = NO 3 – and B' = alkali metal is reported, complementing earlier studies of the [Me 4 N] 2 [KB(NO 3 ) 6 ] (B = Am, Cm, La–Nd, Sm–Lu, Y) (Me 4 N = (CH 3 ) 4 N + ) compounds. In the present efforts, the synthetic phase space of these systems is explored by varying the identity of the alkali metal ion at the B'-site. Herein, we report three new series of the form [Me 4 N] 2 [B'B(NO 3 ) 6 ] (B = La–Nd, Sm–Gd; B' = Na, Rb, Cs). The early members of the Na-series crystallize in the trigonal space group R3̅ from La to Nd where a phase transition occurs in the phase between 273 and 300 K, going from R3̅ to the high-symmetry, cubic space group Fm3̅m. The preceding trigonal members of the Na-series also undergo phase transitions to cubic symmetry at temperatures above 300 K, establishing a decreasing trend in the phase-transition temperature. The remainder of the Na-series, as well as the Rb- and Cs-series, all crystallize in Fm3̅m at 300 K. The temperature-dependent phase behavior of the synthesized phases is studied via variable-temperature spectroscopic methods and high-resolution powder X-ray diffractometry. All phases were characterized via single-crystal and powder X-ray diffraction and Fourier transform infrared (FT-IR) and Raman spectroscopic methods. These results demonstrate the versatility of the perovskite structure type to include rare earth ions, nitrate ions, and a suite of alkali metal ions and serve as a foundation for the design of functional rare earth hybrid double perovskite materials such as those possessing useful multiferroic, optical, and magnetic properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

University of Washington Harborview Research and Training Building Environmental Sample Plan for Cs-137 in Soils and Sediments

On May 2, 2019, a release of Cs-137 from a breached sealed source containing 2,800 curies (Ci) (1E14 Bq) of Cesium-137 (Cs-137) occurred at the University of Washington (UW) Harborview Research and Training Building (HRB). The release occurred during removal of the source from its holder within a portable hot cell in the second floor loading dock area. The loading dock and northeast corner of the building above the ground floor were heavily impacted by the release, while the remaining portions of the building and the exterior of the building were minimally impacted.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Perovskite-Derivative Valleytronics

Halide perovskites are revolutionizing the renewable energy sector owing to their high photovoltaic efficiency, low manufacturing cost, and flexibility. Their remarkable mobility and long carrier lifetime are also valuable for information technology, but fundamental challenges like poor stability under an electric field prevent realistic applications of halide perovskites in electronics. Here, it is discovered that valleytronics is a promising route to leverage the advantages of halide perovskites and derivatives for information storage and processing. The synthesized all-inorganic lead-free perovskite derivative, Cs 3 Bi 2 I 9 , exhibits strong light-matter interaction and parity-dependent optically addressable valley degree of freedom. In this work, robust optical helicity in all odd-layer-number crystals with inversion symmetry breaking is observed, indicating excitonic coherence extending well beyond 11 layers. The excellent optical and valley properties of Cs 3 Bi 2 I 9 arise from the unique parallel bands, according to first principles calculations. This discovery points to new materials design principles for scalable valleytronic devices and demonstrates the promise of perovskite derivatives beyond energy applications.

2D materials↗

Materials Data on CsHS2(O3F)2 by Materials Project

Cs(FO2SOH)OSO2F crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Cs1+ is bonded to ten O2- and two equivalent F1- atoms to form distorted CsO10F2 cuboctahedra that share corners with eight equivalent SO3F tetrahedra, edges with four equivalent CsO10F2 cuboctahedra, and edges with two equivalent SO3F tetrahedra. There are a spread of Cs–O bond distances ranging from 3.14–3.57 Å. Both Cs–F bond lengths are 3.31 Å. H1+ is bonded in a linear geometry to two equivalent O2- atoms. Both H–O bond lengths are 1.21 Å. S6+ is bonded to three O2- and one F1- atom to form SO3F tetrahedra that share corners with four equivalent CsO10F2 cuboctahedra and an edgeedge with one CsO10F2 cuboctahedra. There is two shorter (1.44 Å) and one longer (1.50 Å) S–O bond length. The S–F bond length is 1.62 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to two equivalent Cs1+ and one S6+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to two equivalent Cs1+ and one S6+ atom. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to one Cs1+, one H1+, and one S6+ atom. F1- is bonded in a single-bond geometry to one Cs1+ and one S6+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Cs3Rb5Mo12(P3O17)4 by Materials Project

Cs3Rb5Mo12(P3O17)4 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are three inequivalent Cs sites. In the first Cs site, Cs is bonded in a 1-coordinate geometry to ten O atoms. There are a spread of Cs–O bond distances ranging from 3.19–3.56 Å. In the second Cs site, Cs is bonded in a 1-coordinate geometry to ten O atoms. There are a spread of Cs–O bond distances ranging from 3.19–3.56 Å. In the third Cs site, Cs is bonded in a 1-coordinate geometry to ten O atoms. There are a spread of Cs–O bond distances ranging from 3.19–3.56 Å. There are five inequivalent Rb sites. In the first Rb site, Rb is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Rb–O bond distances ranging from 2.86–3.31 Å. In the second Rb site, Rb is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Rb–O bond distances ranging from 2.86–3.31 Å. In the third Rb site, Rb is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Rb–O bond distances ranging from 2.86–3.31 Å. In the fourth Rb site, Rb is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Rb–O bond distances ranging from 2.86–3.31 Å. In the fifth Rb site, Rb is bonded in a 1-coordinate geometry to ten O atoms. There are a spread of Rb–O bond distances ranging from 3.18–3.58 Å. There are ten inequivalent Mo sites. In the first Mo site, Mo is bonded to six O atoms to form distorted MoO6 octahedra that share a cornercorner with one MoO6 octahedra and corners with three PO4 tetrahedra. The corner-sharing octahedral tilt angles are 32°. There are a spread of Mo–O bond distances ranging from 1.74–2.31 Å. In the second Mo site, Mo is bonded to six O atoms to form distorted MoO6 octahedra that share a cornercorner with one MoO6 octahedra and corners with three PO4 tetrahedra. The corner-sharing octahedral tilt angles are 32°. There are a spread of Mo–O bond distances ranging from 1.74–2.31 Å. In the third Mo site, Mo is bonded to six O atoms to form distorted MoO6 octahedra that share a cornercorner with one MoO6 octahedra and corners with three PO4 tetrahedra. The corner-sharing octahedral tilt angles are 32°. There are a spread of Mo–O bond distances ranging from 1.74–2.31 Å. In the fourth Mo site, Mo is bonded to six O atoms to form distorted MoO6 octahedra that share corners with five PO4 tetrahedra. There are a spread of Mo–O bond distances ranging from 1.71–2.19 Å. In the fifth Mo site, Mo is bonded to six O atoms to form distorted MoO6 octahedra that share corners with five PO4 tetrahedra. There are a spread of Mo–O bond distances ranging from 1.71–2.19 Å. In the sixth Mo site, Mo is bonded to six O atoms to form distorted MoO6 octahedra that share corners with five PO4 tetrahedra. There are a spread of Mo–O bond distances ranging from 1.71–2.19 Å. In the seventh Mo site, Mo is bonded to six O atoms to form distorted MoO6 octahedra that share corners with five PO4 tetrahedra. There are a spread of Mo–O bond distances ranging from 1.71–2.19 Å. In the eighth Mo site, Mo is bonded to six O atoms to form distorted MoO6 octahedra that share a cornercorner with one MoO6 octahedra and corners with four PO4 tetrahedra. The corner-sharing octahedral tilt angles are 32°. There are a spread of Mo–O bond distances ranging from 1.73–2.21 Å. In the ninth Mo site, Mo is bonded to six O atoms to form distorted MoO6 octahedra that share a cornercorner with one MoO6 octahedra and corners with four PO4 tetrahedra. The corner-sharing octahedral tilt angles are 32°. There are a spread of Mo–O bond distances ranging from 1.73–2.22 Å. In the tenth Mo site, Mo is bonded to six O atoms to form distorted MoO6 octahedra that share a cornercorner with one MoO6 octahedra and corners with four PO4 tetrahedra. The corner-sharing octahedral tilt angles are 32°. There are a spread of Mo–O bond distances ranging from 1.73–2.21 Å. There are twelve inequivalent P sites. In the first P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 35–44°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. In the second P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 35–44°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. In the third P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 35–45°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. In the fourth P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 35–44°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. In the fifth P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 29–46°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. In the sixth P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 29–45°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. In the seventh P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 29–45°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. In the eighth P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 29–45°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. In the ninth P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 20–49°. There are a spread of P–O bond distances ranging from 1.54–1.56 Å. In the tenth P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 20–49°. There are a spread of P–O bond distances ranging from 1.54–1.56 Å. In the eleventh P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 20–49°. There are a spread of P–O bond distances ranging from 1.54–1.56 Å. In the twelfth P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four MoO6 octahedra. The corner-sharing octahedra tilt angles range from 20–49°. There are a spread of P–O bond distances ranging from 1.54–1.56 Å. There are sixty-eight inequivalent O sites. In the first O site, O is bonded in a distorted single-bond geometry to one Cs and one Mo atom. In the second O site, O is bonded in a distorted single-bond geometry to one Cs and one Mo atom. In the third O site, O is bonded in a distorted single-bond geometry to one Rb and one Mo atom. In the fourth O site, O is bonded in a distorted single-bond geometry to one Cs and one Mo atom. In the fifth O site, O is bonded in a 2-coordinate geometry to one Rb, one Mo, and one P atom. In the sixth O site, O is bonded in a 2-coordinate geometry to one Cs, one Mo, and one P atom. In the seventh O site, O is bonded in a 2-coordinate geometry to one Cs, one Mo, and one P atom. In the eighth O site, O is bonded in a 2-coordinate geometry to one Cs, one Mo, and one P atom. In the ninth O site, O is bonded in a 2-coordinate geometry to two Rb, one Mo, and one P atom. In the tenth O site, O is bonded in a 2-coordinate geometry to one Cs, one Rb, one Mo, and one P atom. In the eleventh O site, O is bonded in a 2-coordinate geometry to one Cs, one Rb, one Mo, and one P atom. In the twelfth O site, O is bonded in a 2-coordinate geometry to one Cs, one Rb, one Mo, and one P atom. In the thirteenth O site, O is bonded in a bent 150 degrees geometry to one Mo and one P atom. In the fourteenth O site, O is bonded in a bent 150 degrees geometry to one Mo and one P atom. In the fifteenth O site, O is bonded in a bent 150 degrees geometry to one Mo and one P atom. In the sixteenth O site, O is bonded in a bent 150 degrees geometry to one Mo and one P atom. In the seventeenth O site, O is bonded in a 1-coordinate geometry to one Cs, one Mo, and one P atom. In the eighteenth O site, O is bonded in a 1-coordinate geometry to one Rb, one Mo, and one P atom. In the nineteenth O site, O is bonded in a 1-coordinate geometry to one Cs, one Mo, and one P atom. The O–Mo bond length is 2.21 Å. In the twentieth O site, O is bonded in a 1-coordinate geometry to one Cs, one Mo, and one P atom. In the twenty-first O site, O is bonded in a distorted bent 150 degrees geometry to two Mo atoms. In the twenty-second O site, O is bonded in a distorted bent 150 degrees geometry to two Mo atoms. In the twenty-third O site, O is bonded in a distorted bent 150 degrees geometry to two Mo atoms. There are one shorter (1.77 Å) and one longer (2.31 Å) O–Mo bond lengths. In the twenty-fourth O site, O is bonded in a distorted bent 150 degrees geometry to two Mo atoms. In the twenty-fifth O site, O is bonded in a bent 150 degrees geometry to one Mo and one P atom. In the twenty-sixth O site, O is bonded in a bent 150 degrees geometry to one Mo and one P atom. In the twenty-seventh O site, O is bonded in a bent 150 degrees geometry to one Mo and one P atom. In the twenty-eighth O site, O is bonded in a bent 150 degrees geometry to one Mo and one P atom. The O–Mo bond length is 2.01 Å. In the twenty-ninth O site, O is bonded in a 2-coordinate geometry to one Cs, one Mo, and one P atom. In the thirtieth O site, O is bonded in a 2-coordinate geometry to one Rb, one Mo, and one P atom. In the thirty-first O site, O is bonded in a 2-coordinate geometry to one Cs, one Mo, and one P atom. In the thirty-second O site, O is bonded in a 2-coordinate geometry to one Cs, one Mo, and one P atom. In the thirty-third O site, O is bonded in a single-bond geometry to two Rb and one Mo atom. In the thirty-fourth O site, O is bonded in a single-bond geometry to two Rb and one Mo atom. In the thirty-fifth O site, O is bonded in a single-bond geometry to two Rb and one Mo atom. The O–Mo bond length is 1.73 Å. In the thirty-sixth O site, O is bonded in a single-bond geometry to two Rb and one Mo atom. In the thirty-seventh O site, O is bonded in a 2-coordinate geometry to one Cs, one Mo, and one P atom. In the thirty-eighth O site, O is bonded in a 2-coordinate geometry to one Cs, one Mo, and one P atom. In the thirty-ninth O site, O is bonded in a 2-coordinate geometry to one Cs, one Mo, and one P atom. The O–Mo bond length is 2.04 Å. In the fortieth O site, O is bonded in a distorted bent 150 degrees geometry to one Rb, one Mo, and one P atom. In the forty-first O site, O is bonded in a distorted single-bond geometry to one Rb and one Mo atom. In the forty-second O site, O is bonded in a distorted single-bond geometry to one Rb and one Mo atom. In the forty-third O site, O is bonded in a distorted bent 120 degrees geometry to one Rb and one Mo atom. In the forty-fourth O site, O is bonded in a distorted single-bond geometry to one Rb and one Mo atom. The O–Mo bond length is 1.74 Å. In the forty-fifth O site, O is bonded in a 1-coordinate geometry to one Cs, one Rb, one Mo, and one P atom. In the forty-sixth O site, O is bonded in a 1-coordinate geometry to two Rb, one Mo, and one P atom. In the forty-seventh O site, O is bonded in a 1-coordinate geometry to one Cs, one Rb, one Mo, and one P atom. In the forty-eighth O site, O is bonded in a 1-coordinate geometry to one Cs, one Rb, one Mo, and one P atom. In the forty-ninth O site,

36 MATERIALS SCIENCE↗

Pressure-Induced Metal-like Transport and Magnetoresistance in a Au 2+ –Au 3+ Halide Perovskite

The Cs 4 Au II Au III 2 Cl 12 perovskite (1), featuring AuCl 4 trimers separated by vacancies, enables the first high-pressure study of Au 2+/3+ mixed-valence. Our computational analysis of the gold frontier orbitals suggests that the Au 2+ →Au 3+ intervalence charge transfer (IVCT) occurs across the vacancies. Computational structures indicate that these vacancies rapidly shrink with pressure and the Au 2+ and Au 3+ coordination spheres become very similar at the phase transition to nearly cubic symmetry at ca. 15 GPa─enabling facile IVCT. Although the activation energy of conductivity of 0.73(4) meV and far-infrared absorption indicate a small but nonzero bandgap, ambient thermal energy drives the IVCT, affording metallic properties: prominent infrared reflectivity and transport values of 10 2 S·cm –1 . This prompted us to perform the first high-pressure studies of magnetoresistance (MR) and Hall effect in halide perovskites. At 16 GPa, the MR increases by 9.3% at 2 K and 9 T; this value is maintained up to 27 GPa, when a local distortion drives electronic localization. By globally fitting the MR and Hall resistance to a two-carrier model we quantify how the carrier densities and mobilities evolve with pressure. Thus, metal-like transport and MR in 1 is driven by a pressure-induced transition from localized to partially delocalized mixed-valence.

Deschene, Christina R. [Stanford University, CA (U↗

Materials Data on Cs10Si7O9 by Materials Project

Cs10Si7O9 crystallizes in the monoclinic P2/c space group. The structure is three-dimensional. there are ten inequivalent Cs sites. In the first Cs site, Cs is bonded in a 1-coordinate geometry to one Si and one O atom. The Cs–Si bond length is 4.04 Å. The Cs–O bond length is 2.87 Å. In the second Cs site, Cs is bonded in a distorted single-bond geometry to two Si and one O atom. There are one shorter (3.61 Å) and one longer (3.72 Å) Cs–Si bond lengths. The Cs–O bond length is 2.92 Å. In the third Cs site, Cs is bonded in a distorted single-bond geometry to three Si and one O atom. There are a spread of Cs–Si bond distances ranging from 3.71–3.86 Å. The Cs–O bond length is 2.91 Å. In the fourth Cs site, Cs is bonded in a 5-coordinate geometry to one Si and four O atoms. The Cs–Si bond length is 3.64 Å. There are a spread of Cs–O bond distances ranging from 3.01–3.14 Å. In the fifth Cs site, Cs is bonded in a 5-coordinate geometry to one Si and four O atoms. The Cs–Si bond length is 3.67 Å. There are a spread of Cs–O bond distances ranging from 2.98–3.13 Å. In the sixth Cs site, Cs is bonded in a 1-coordinate geometry to one Si and six O atoms. The Cs–Si bond length is 4.04 Å. There are a spread of Cs–O bond distances ranging from 2.94–3.55 Å. In the seventh Cs site, Cs is bonded in a 2-coordinate geometry to four Si and two O atoms. There are a spread of Cs–Si bond distances ranging from 3.82–4.14 Å. There are one shorter (3.03 Å) and one longer (3.11 Å) Cs–O bond lengths. In the eighth Cs site, Cs is bonded in a 1-coordinate geometry to two Si and six O atoms. There are one shorter (3.74 Å) and one longer (4.12 Å) Cs–Si bond lengths. There are a spread of Cs–O bond distances ranging from 2.97–3.46 Å. In the ninth Cs site, Cs is bonded in a 2-coordinate geometry to four Si and three O atoms. There are a spread of Cs–Si bond distances ranging from 3.89–4.02 Å. There are a spread of Cs–O bond distances ranging from 3.11–3.23 Å. In the tenth Cs site, Cs is bonded in a 2-coordinate geometry to three Si and six O atoms. There are a spread of Cs–Si bond distances ranging from 3.91–3.98 Å. There are a spread of Cs–O bond distances ranging from 3.11–3.78 Å. There are eight inequivalent Si sites. In the first Si site, Si is bonded in a 9-coordinate geometry to six Cs and three Si atoms. There are two shorter (2.43 Å) and one longer (2.44 Å) Si–Si bond lengths. In the second Si site, Si is bonded to four O atoms to form corner-sharing SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.62–1.70 Å. In the third Si site, Si is bonded in a 8-coordinate geometry to five Cs and three Si atoms. There are one shorter (2.41 Å) and one longer (2.46 Å) Si–Si bond lengths. In the fourth Si site, Si is bonded in a 9-coordinate geometry to six Cs and three Si atoms. The Si–Si bond length is 2.45 Å. In the fifth Si site, Si is bonded to four O atoms to form corner-sharing SiO4 tetrahedra. There is two shorter (1.62 Å) and two longer (1.69 Å) Si–O bond length. In the sixth Si site, Si is bonded to four O atoms to form corner-sharing SiO4 tetrahedra. There is two shorter (1.62 Å) and two longer (1.70 Å) Si–O bond length. In the seventh Si site, Si is bonded in a 2-coordinate geometry to five Cs and three Si atoms. In the eighth Si site, Si is bonded to four O atoms to form corner-sharing SiO4 tetrahedra. There is two shorter (1.62 Å) and two longer (1.70 Å) Si–O bond length. There are ten inequivalent O sites. In the first O site, O is bonded in a 2-coordinate geometry to three Cs and two Si atoms. In the second O site, O is bonded in a distorted single-bond geometry to three Cs and one Si atom. In the third O site, O is bonded in a 2-coordinate geometry to two equivalent Cs and two equivalent Si atoms. In the fourth O site, O is bonded in a distorted single-bond geometry to five Cs and one Si atom. In the fifth O site, O is bonded in a 2-coordinate geometry to two equivalent Cs and two equivalent Si atoms. In the sixth O site, O is bonded in a distorted single-bond geometry to five Cs and one Si atom. In the seventh O site, O is bonded in a distorted single-bond geometry to five Cs and one Si atom. In the eighth O site, O is bonded in a distorted single-bond geometry to four Cs and one Si atom. In the ninth O site, O is bonded in a distorted single-bond geometry to four Cs and one Si atom. In the tenth O site, O is bonded in a 2-coordinate geometry to three Cs and two Si atoms.

36 MATERIALS SCIENCE↗

Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species

Aluminate salts precipitated from caustic alkaline solutions exhibit a correlation between the anionic speciation and the identity of the alkali cation in the precipitate, with the aluminate ions occurring either in monomeric (Al(OH) 4 – ) or dimeric (Al 2 O(OH) 6 2– ) forms. The origin of this correlation is poorly understood as are the roles that oligomeric aluminate species play in determining the solution structure, prenucleation clusters, and precipitation pathways. Characterization of aluminate solution speciation with vibrational spectroscopy results in spectra that are difficult to interpret because the ions access a diverse and dynamic configurational space. To investigate the Al(OH) 4 – and Al 2 O(OH) 6 2– anions within a well-defined crystal lattice, inelastic neutron scattering (INS) and Raman spectroscopic data were collected and simulated by density functional theory for K 2 [Al 2 O(OH) 6 ], Rb 2 [Al 2 O(OH) 6 ], and Cs[Al(OH) 4 ]·2H 2 O. These structures capture archetypal solution aluminate species: the first two salts contain dimeric Al 2 O(OH) 6 2– anions, while the third contains the monomeric Al(OH) 4 – anion. Here, comparisons were made to the INS and Raman spectra of sodium aluminate solutions frozen in a glassy state. In contrast to solution systems, the crystal lattice of the salts results in well-defined vibrations and associated resolved bands in the INS spectra. The use of a theory-guided analysis of the INS of this solid alkaline aluminate series revealed that differences were related to the nature of the hydrogen-bonding network and showed that INS is a sensitive probe of the degree of completeness and strength of the bond network in hydrogen-bonded materials. Results suggest that the ionic size may explain cation-specific differences in crystallization pathways in alkaline aluminate salts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Crystal growth and scintillation properties of new ytterbium-activated scintillators Cs 4 CaI 6 :Yb and Cs 4 SrI 6 :Yb

Yb 2+ was investigated as a potential alternative activator for Cs 4 SrI 6 and Cs 4 CaI 6 scintillators for the first time, as opposed to the previously studied Eu2+ activator. Single crystals with nominal Yb 2+ concentrations of 0.5 mol%, 1 mol%, and 3 mol% were grown in Ø7 mm ampoules using the vertical Bridgman method. Luminescence and scintillation properties were evaluated as a function of Yb 2+ concentration and host compound. Here, the 5d → 4f electronic transition of Yb 2+ was observed for both the Sr- and Ca-containing compositions. X-ray induced radioluminescence emission was centered between 449 nm and 463 nm depending on Yb 2+ concentration and host compound. Both the spin-allowed and spin-forbidden transitions were observed in photoluminescence emission spectra and were centered at 446 nm and 476 nm, respectively, for both compounds. The best scintillation performance was achieved with Cs 4 CaI 6 :Yb 1 mol%, which had a 3.5% energy resolution at 662 keV and 43,000 ph/MeV light yield. To our knowledge this is the best energy resolution ever reported for a Yb 2+ -doped scintillator. Additional Cs 4 CaI 6 :Yb 1% crystals were grown in Ø12 mm ampoules to investigate the size dependence of scintillation properties, as well as crystal homogeneity.

36 MATERIALS SCIENCE↗

Influence of Cs Promoter on Ethanol Steam-Reforming Selectivity of Pt/m-ZrO 2 Catalysts at Low Temperature

The decarboxylation pathway in ethanol steam reforming ultimately favors higher selectivity to hydrogen over the decarbonylation mechanism. The addition of an optimized amount of Cs to Pt/m-ZrO 2 catalysts increases the basicity and promotes the decarboxylation route, converting ethanol to mainly H 2 , CO 2 , and CH 4 at low temperature with virtually no decarbonylation being detected. This offers the potential to feed the product stream into a conventional methane steam reformer for the production of hydrogen with higher selectivity. DRIFTS and the temperature-programmed reaction of ethanol steam reforming, as well as fixed bed catalyst testing, revealed that the addition of just 2.9% Cs was able to stave off decarbonylation almost completely by attenuating the metallic function. This occurs with a decrease in ethanol conversion of just 16% relative to the undoped catalyst. In comparison with our previous work with Na, this amount is—on an equivalent atomic basis—just 28% of the amount of Na that is required to achieve the same effect. Thus, Cs is a much more efficient promoter than Na in facilitating decarboxylation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Stabilization of Preternatural Barium Oxidation States as an Unexpected Byproduct of β-Decay: Discovery of a New Halide Semiconductor Alloy

137 Cs has a wide range of roles in the nuclear industry. The solid material, safely encapsulated in CsCl as 137 CsCl, is stored as fission product waste from nuclear power production and legacy waste from nuclear weapons production; it has also served as a radiation source in food and sewage irradiators as well as medical devices. However, because of the solubility of the chloride salt and the relatively high specific activity of 137 Cs, damaged or broken capsules can lead to severe radiological accidents. Safe capsule design and material recycling are complicated by the unclear structural evolution during β-decay, which remains ambiguous due to the differing oxidation states of Cs (1+) and Ba (2+). Here, in this study, we use first-principles calculations to investigate the evolving structure–property relationships of Cs 1–x Ba x Cl during β-decay. Despite the well-established 2+ formal oxidation state of alkali-earth metals, we find that Ba 1+ can be stabilized in the form of a mixed-valence alloy at low concentrations. Specifically, we identify three regimes for the β-decay of 137 Cs into CsCl: Ba-doped CsCl (Ba ≤ 14%), wherein Ba has the expected 2+ oxidation state; Cs–Ba–Cl alloys, where Ba has a mix of the usual Ba 2+ and highly unusual Ba 1+ oxidation state in the form of a quasi-disordered mixed-valence alloy (Ba = 25%); and phase separation into a CsCl + BaCl 2 + Ba (m) mechanical mixture, where Ba reverts to its expected 2+ oxidation state (Ba > 25%). Surprisingly, the Cs 0.75 Ba 0.25 Cl mixed-valence alloy is a narrow indirect band gap semiconductor (1.05 eV) despite the insulating nature of both CsCl and BaCl 2 . It also exhibits strongly excitonic polarized optical properties, has glass-like ultralow thermal conductivity (directional average of 0.21 W/mK at 300 K), and shows greater resistance to deformation under both tensile and volumetric strengths compared with the original CsCl structure (e.g., shear and Young’s modulus of 9.04 and 31.62 GPa, respectively). These findings imply that transmutation of 137 Cs leads to highly unusual chemical bonding that stabilizes Ba 1+ in local regions of the quasi-disordered Cs 0.25 Ba 0.75 Cl, resulting in anomalous physical properties. Moreover, this discovery provides valuable insight for safe nuclear waste capsule design, which can aid in preventing environmental or human exposure to radioactive materials.

Fuhr, Addis S. [Oak Ridge National Laboratory (ORN↗