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DOE OSTI2018

Analysis of Krypton-85 Legacy Waste Forms: Part II

During a removal of legacy materials from one hot cell at the Idaho National Laboratory in 2010, five metal capsules and some loose zeolite material were identified as krypton (Kr) immobilization test specimens produced in the late 1970s under the Airborne Waste Management Program (AWMP). This AWMP research and development effort examined the encapsulation of 85Kr within a collapsed zeolite structure for use as a potential waste form for long-term storage. The recovered capsules appeared to have been placed to the side and remained untouched after the AWMP was halted in the mid-1980s. These reclaimed capsules and loose material presented a unique opportunity to study a potential 85 Kr waste form after three half-lives had elapsed. The first phase of this study included two parts: The first was to assess the physical condition of the capsule walls, and the second was to examine the Kr-containing material within the capsules. The first part of this study was previously reported and noted that substantial corrosion was observed throughout each capsule wall of the two previously breached capsules that were examined. One of these capsules had been hot isostatic pressed (HIPed) and one was not HIPed. The second part of the study examined the materials contained in the two previously breached capsules. There appears to be a relatively uniform distribution of Kr and rubidium throughout the pellets examined. The chemical composition of the pellets appears to be consistent with 5A molecular sieves. The material contained within the HIPed capsules showed ~1 at. % lead (Pb). The origin of the Pb is currently indeterminate. X-ray diffraction analysis shows a significant shift from the 5A structure, most likely due to the Kr encapsulation/sintering process that occurred when the samples were made. Calculations based on the energy dispersive spectrometry elemental analysis show a residual Kr level within the pellets that is within a factor of 2 of the reported Kr capacities for this type of processed material. This provides a clear indication that a significant fraction of the Kr initially encapsulated in the material remained within the waste form even following a significant breach of the capsule wall. As a result, it would appear that this Kr immobilization method, even in non-HIPed form, is very promising as a waste form for long-term storage. The successful analysis of these two breached capsules forms a solid basis for the future analysis of the remaining unbreached capsules, which offers the opportunity to provide an even more complete understanding of the long-term Kr retention performance of this promising waste form.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

NASA NTRS1985

Environmental stability graphite/PMR-15 composites

During the past few years the Boeing Company was screening graphite composites for use in hot areas of engine nacelle structure. Structural and thermal analyses have shown that there is the potential for a 25 to 30 percent weight savings by using a graphite polyimide (Gr/PI) composite material in this type of structure. Work conducted on the NASA CASTS program (Composites for Advanced Space Transportation Systems) amply demonstrated the capability of Graphite/PMR-15 for short term service (125 hours) at temperatures up to 589 K (600 F). In addition, the CASTS program demonstrated that large structures could be fabricated using Gr/PMR-15. In commercial applications, however, the requirement exists for long term service capability (tens of thousands of hours) at temperatures ranging upwards from 449 K (350 F). The results of Graphite/PMR-15 materials characterization efforts conducted at Boeing are presented with emphasis on materials properties after isothermal aging at temperatures of 449 K (350 F) and above.

Sheppard, C. H.↗

NASA NTRS2014

Aqueous Alteration of Enstatite Chondrites

The Kaidun meteorite is different from all other meteorites [1], consisting largely of a mixture of “incompatible” types of meteoritic material – carbonaceous and enstatite chondrites, i.e. corre-sponding to the most oxidized and the most reduced samples of meteorite materials, including CI1, CM1-2, CV3, EH3-5, and EL3. In addition to these, minor amounts of ordinary and R chondrites are present. In addition, approximately half of the Kaidun lithologies are new materials not known as separate meteorites. Among these are aqueously altered enstatite chondrites [1], which are of considerable interest because they testify that not all reduced asteroids escaped late-stage oxidation, and hydrolysis, and also because hydrated poorly crystalline Si-Fe phase, which in turn is re-placed by serpentine (Figs 3-5). In the end the only indication of the original presence of metal is the re-sidual carbides. In other enstatite chondrite lithogies (of uncertain type) original silicates and metal have been thoroughly replaced by an assemblage of authi-genic plagioclase laths, calcite boxwork, and occasion-al residual grains of silica, Cr-rich troilite, ilmenite, and rare sulfides including heideite (Fig. 6). Fe and S have been largely leached from the rock (Fig. 4). Again the accessory phases are the first clue to the original character of the rock, which can be verified by O isotopes. It is fortunate that Kaidun displays every step of the alteration process.

Zolensky, M. E.↗

DOE OSTI2014

Method of fabricating a back-contact solar cell and device thereof

Methods of fabricating back-contact solar cells and devices thereof are described. A method of fabricating a back-contact solar cell includes forming an N-type dopant source layer and a P-type dopant source layer above a material layer disposed above a substrate. The N-type dopant source layer is spaced apart from the P-type dopant source layer. The N-type dopant source layer and the P-type dopant source layer are heated. Subsequently, a trench is formed in the material layer, between the N-type and P-type dopant source layers.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Direct synthesis and characterization of mixed-valent Li 0.5$-$δ CoPO 4 , a Li-deficient derivative of the Cmcm polymorph of LiCoPO 4

While the majority of research activities on LiCoPO 4 is focussed on the thermodynamically stable olivine-type Pnma polymorph, the metastable Pna 2 1 and Cmcm modifications have recently attracted considerable attention due to their interesting material properties. In this study, we present the first Li-deficient structural derivative of the Cmcm modification with the nominal composition Li 0.5–δ CoPO 4 . As opposed to the substoichiometric olivine ( Pnma ) phases Li x CoPO 4 (x = 0; 2/3), which are exclusively accessible by electrochemical or chemical Li extraction techniques, this is also the first time that a direct soft-chemical synthesis route towards a Li x CoPO 4 -type material is accomplished. X-ray and neutron diffraction studies indicate that Cmcm -type Li 0.5–δ CoPO 4 shows vacancies on both the Li and Co sites, whereas X-ray absorption spectra demonstrate that the structure features heterovalent Co ions (+2/+3) to compensate for the Li deficit. Magnetic measurements reveal a long-range antiferromagnetic order below 10.5 K. A thorough investigation of the thermal stability using thermogravimetric analysis, differential scanning calorimetry, and temperature-dependent in situ X-ray powder diffraction demonstrates that Li 0.5–δ CoPO 4 is metastable and exhibits a complex, multi-step thermal decomposition mechanism. In the first step at 394 °C, it decomposes to α-Co 2 P 2 O 7 ( P 2 1 /c) and LiCoPO 4 ( Cmcm ) upon O 2 release. The LiCoPO 4 ( Cmcm ) intermediate is then irreversibly transformed to olivine-type LiCoPO 4 (Pnma) at 686 °C. Furthermore, the material properties of Li 0.5–δ CoPO 4 are further compared to the fully lithiated, isostructural LiCoPO 4 ( Cmcm ) phase, for which an improved structure solution as well as Co L 2,3 -edge X-ray absorption spectra are reported for the first time.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Searching for light echoes due to circumstellar matter in SNe Ia spectra

We present an analytical model for light echoes (LEs) coming from circumstellar material (CSM) around Type Ia Supernovae (SNe Ia). Using this model we find two spectral signatures at 4100 Å and 6200 Å that are useful to identify LEs during the Lira law phase (between 35 and 80 days after maximum light) coming from nearby CSM at distances of 0.01–0.25 pc. We analyze a sample of 89 SNe Ia divided into two groups according to their B−V decline rate during the Lira law phase, and search for LEs from CSM interaction in the group of SNe with steeper slopes by comparing their spectra with our LE model. We find that a model with LEs + pure extinction from interstellar material (ISM) fits the observed spectra better than a pure ISM extinction model that is constant in time, but we find that a decreasing extinction alone explains the observations better without the need of LEs, possibly implying dust sublimation due to the radiation from the SN.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2019

The importance of phase equilibrium for doping efficiency: iodine doped PbTe

Semiconductor engineering relies heavily on doping efficiency and dopability. Low doping efficiency may cause low mobility and failure to reach target carrier concentrations or even the desired carrier type. Semiconducting thermoelectric materials perform best with degenerate carrier concentrations, meaning high performance in new materials might not be realized experimentally without a route to optimal doping. Doping in the classic PbTe thermoelectric system has been largely successful but reported doping efficiencies can vary, raising concerns about reproducibility. Here, we stress the importance of phase equilibria considerations during synthesis to avoid undesired intrinsic defects leading to sub-optimal doping. By saturation annealing at 973 K, we decidedly fix the composition in single crystal iodine-doped PbTe samples to be Pb-rich or Te-rich without introducing impurity phases. We show that, regardless of iodine concentration, degenerate n-type carrier concentrations with ideal doping efficiency require Pb-rich compositions. Electrons in Te-rich samples are heavily compensated by charged intrinsic Pb vacancy defects. From Hall effect measurements and a simple defect model supported by modern defect calculations, we map out the 973 K ternary Pb–Te–I phase diagram to explicitly link carrier concentration and composition. Furthermore, we discuss unintentional composition changes due to loss of volatile Te during synthesis and measurements. The methods and concepts applied here may guide doping studies on other lead chalcogenide systems as well as any doped, complex semiconductor.

36 MATERIALS SCIENCE↗

NASA NTRS2006

Aerogel/Particle Composites for Thermoelectric Devices

Optimizing solution chemistry and the addition of titania and fumed silica powder reduces shrinkage. These materials would serve to increase thermal efficiency by providing thermal insulation to suppress lateral heat leaks. They would also serve to prolong operational lifetime by suppressing sublimation of certain constituents of thermoelectric materials (e.g., sublimation of Sb from CoSb3) at typical high operating temperatures. [The use of pure silica aerogels as cast-in-place thermal-insulation and sublimation-suppression materials was described in "Aerogels for Thermal Insulation of Thermoelectric Devices" (NPO-40630), NASA Tech Briefs, Vol. 30, No. 7 (July 2006), page 50.] A silica aerogel is synthesized in a solgel process that includes preparation of a silica sol, gelation of the sol, and drying of the gel in a solvent at a supercritical temperature and pressure. The utility of pure silica aerogel is diminished by a tendency to shrink (and, therefore, also to crack) during the gelation and supercritical-drying stages. Moreover, to increase suppression of sublimation, it is advantageous to make an aerogel having greater density, but shrinkage and cracking tend to increase with density. A composite material of the type under investigation consists mostly of titania oxide powder particles and a small addition of fumed silica powder, which are mixed into the sol along with other ingredients prior to the gelation stage of processing. The silica aerogel and fumed silica act as a binder, gluing the titania particles together. It is believed that the addition of fumed silica stiffens the aerogel network and reduces shrinkage during the supercritical-drying stage. Minimization of shrinkage enables establishment of intimate contact between thermoelectric legs and the composite material, thereby maximizing the effectiveness of the material for thermal insulation and suppression of sublimation. To some extent, the properties of the composite can be tailored via the proportions of titania and other ingredients. In particular (see figure), the addition of a suitably large proportion of titania (e.g., 0.6 g/cu cm) along with a 10-percent increase in the amount of tetraethylorthosilicate [TEOS (an ingredient of the sol)] to an aerogel component having a density 40 mg/cm3makes it possible to cast a high-average-density (>0.1 g/cm3) aerogel/particle composite having low shrinkage (2.3 percent).

Paik, Jong-Ah↗

DOE OSTI2016

Synthesis optimisation and characterisation of the organic-inorganic layered materials ZnS(m-xylylenediamine){sub 1/2} and ZnS(p-xylylenediamine){sub 1/2}

Hybrid organic-inorganic layered materials of the type ZnS(amine){sub 1/2}, where amine=m-xylylenediamine (MXDA) or p-xylylenediamine (PXDA), were synthesised using a simple solvothermal method. Since the samples crystallised in the form of very fine powder, X-ray powder diffraction techniques were used for structural characterisation. The crystal structure studies, involving direct methods, show that both compounds crystallised in the orthorhombic crystal system, but in different space groups: ZnS(MXDA){sub 1/2} in non-centrosymmetric Ccm2{sub 1}, ZnS(PXDA){sub 1/2} in centrosymmetric Pcab. The obtained materials are built according to similar orders: semiconducting monolayers with the formula ZnS, parallel to the (010) plane, are separated by diamines. The organic and inorganic fragments are connected by covalent bonds between metal atoms of the layers and nitrogen atoms of the amino groups. The optical properties of the hybrid materials differ from those of their bulk counterpart. In both compounds a blue-shift of about 0.8 or 0.9 eV was observed with reference to the bulk phase of ZnS. - Highlights: • New hybrid compounds: ZnS(MXDA){sub 1/2} and ZnS(PXDA){sub 1/2} were obtained. • Hybrids were studied using XRD, TG/DSC, XRK, SEM, UV–vis spectroscopy. • Structures of both materials were solved by powder diffraction methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Direct observation of minibands in a twisted graphene/WS 2 bilayer

Stacking two-dimensional (2D) van der Waals materials with different interlayer atomic registry in a heterobilayer causes the formation of a long-range periodic superlattice that may bestow the heterostructure with properties such as new quantum fractal states or superconductivity. Recent optical measurements of transition metal dichalcogenide (TMD) heterobilayers have revealed the presence of hybridized interlayer electron-hole pair excitations at energies defined by the superlattice potential. The corresponding quasiparticle band structures, so-called minibands, have remained elusive, and no such features have been reported for heterobilayers composed of a TMD and another type of 2D material. We introduce a new x-ray capillary technology for performing microfocused angle-resolved photoemission spectroscopy with a spatial resolution of ~1 μm, and directly observe minibands at certain twist angles in mini Brillouin zones (mBZs). We discuss their origin in terms of initial and final state effects by analyzing their dispersion in distinct mBZs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Universal Mechanism of Viscoplastic Deformation of Metallic Materials Far from Thermodynamics Equilibrium

The article gives results of structure formation in metallic materials after different types of deformation: tungsten after rolling, nickel after thermal cycling and nickel single crystal after rolling, aluminum single crystal after cyclic tension and aluminum alloys (D16, 2024-T3) after impulsive load. We used optical and electron microscopy methods for investigation of deformation structure formation and molecular dynamics method for computer modeling of the processes of plastic deformation (LAMMPS software). The following quantitative parameters were calculated during the simulation: energy of pair interaction, temperature, total cumulative pressure, stress tensor and pressure tensor. The study shows that the plastic flow of metallic materials with any initial structure at certain loading stage can be carried out by homogeneous mass transfer through channels with a liquid-like structure, from which follows that the dislocation mechanism of plastic deformation of crystals has a limited field of application. The main role has a synergistic structure formation in the conditions of distance from thermodynamic equilibrium. The relaxation processes proceed intensively after and during the process of destruction. The results of modeling have shown the possibility of forming channels of hydrodynamic flow without the participation of defects in the initial material.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Production of bio-based materials using photobioreactors with binary cultures

A method, device and system for producing preselected products, (either finished products or preselected intermediary products) from biobased precursors or CO.sub.2 and/or bicarbonate. The principal features of the present invention include a method wherein a binary culture is incubated with a biobased precursor in a closed system to transform at least a portion of the biobased precursor to a preselected product. The present invention provides a method of cultivation that does not need sparging of a closed bioreactor to remove or add a gaseous byproduct or nutrient from a liquid medium. This improvement leads to significant savings in energy consumption and allows for the design of photobioreactors of any desired shape. The present invention also allows for the use of a variety of types of waste materials to be used as the organic starting material.

36 MATERIALS SCIENCE↗

DOE OSTI2022

A bi-layer barrier design for 122-type iron-based superconducting wires and tapes

Iron-based superconducting wires and tapes hold great promise for high-field magnet applications. A promising design for 122-type wires and tapes based on the powder-in-tube method is using silver and copper double-layer sheaths. For this design a heat treatment temperature below ~ 779 °C is required to prevent Ag-Cu liquid formation. However, this may be below the optimal heat treatment temperature for the critical current density, and still cannot prevent Ag-Cu interdiffusion occurring in the solid state. In this work we propose adding a niobium or tantalum or vanadium (or their alloys) barrier layer between the Ag and Cu to solve the Ag-Cu interdiffusion issue, given that the group-VB metals (vanadium, niobium, tantalum) are relatively inert to both Ag and Cu. To investigate the effectiveness of this design, BaFe 1.84 Co 0.16 As 2 wires and tapes with Ag/Cu and Ag/Ta/Cu sheaths, as well as Ba 0.6 K 0.4 Fe 2 As 2 wires and tapes with Ag/Cu and Ag/Nb/Cu sheaths, were fabricated. It was found that both the Ta and Nb layers kept integral after wire drawing, but after a large flat-rolling reduction the Ta layer broke while the Nb layer kept integral. In the tapes with Ag/Cu sheaths (without the Ta or Nb layer) Cu diffused through the Ag layer and into the powder cores during 740 °C heat treatment, while in the tapes with Ag/Nb/Cu sheaths the Nb layer effectively blocked Ag-Cu interdiffusion even at 900 °C. Further, this work demonstrates that Ta is a suitable barrier material for 122-type wires, while Nb is suitable for both wires and tapes. In this design using Ag/Nb (or Ta)/Cu sheaths, we can regard the outer Cu as the conductor matrix while the Ag and Nb (or Ta) serve as two layers of barriers that suppress reactions between the components. Thus, we call this design a “bi-layer barrier” design for 122-type wires and tapes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Method of fabricating a back-contact solar cell and device thereof

14 SOLAR ENERGY↗

DOE OSTI2016

The intercalation chemistry of layered iron chalcogenide superconductors

The iron chalcogenides FeSe and FeS are superconductors composed of two-dimensional sheets held together by van der Waals interactions, which makes them prime candidates for the intercalation of various guest species. We review the intercalation chemistry of FeSe and FeS superconductors and discuss their synthesis, structure, and physical properties. Before we review the latest work in this area, we provide a brief background on the intercalation chemistry of other inorganic materials that exhibit enhanced superconducting properties upon intercalation, which include the transition metal dichalcogenides, fullerenes, and layered cobalt oxides. From past studies of these intercalated superconductors, we discuss the role of the intercalates in terms of charge doping, structural distortions, and Fermi surface reconstruction. We also briefly review the physical and chemical properties of the host materials—mackinawite-type FeS and β-FeSe. The three types of intercalates for the iron chalcogenides can be placed in three categories: 1.) alkali and alkaline earth cations intercalated through the liquid ammonia technique; 2.) cations intercalated with organic amines such as ethylenediamine; and 3.) layered hydroxides intercalated during hydrothermal conditions. A recurring theme in these studies is the role of the intercalated guest in electron doping the chalcogenide host and in enhancing the two-dimensionality of the electronic structure by spacing the FeSe layers apart. We end this review discussing possible new avenues in the intercalation chemistry of transition metal monochalcogenides, and the promise of these materials as a unique set of new inorganic two-dimensional systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1993

High temperature composite analyzer (HITCAN) user's manual, version 1.0

This manual describes 'how-to-use' the computer code, HITCAN (HIgh Temperature Composite ANalyzer). HITCAN is a general purpose computer program for predicting nonlinear global structural and local stress-strain response of arbitrarily oriented, multilayered high temperature metal matrix composite structures. This code combines composite mechanics and laminate theory with an internal data base for material properties of the constituents (matrix, fiber and interphase). The thermo-mechanical properties of the constituents are considered to be nonlinearly dependent on several parameters including temperature, stress and stress rate. The computation procedure for the analysis of the composite structures uses the finite element method. HITCAN is written in FORTRAN 77 computer language and at present has been configured and executed on the NASA Lewis Research Center CRAY XMP and YMP computers. This manual describes HlTCAN's capabilities and limitations followed by input/execution/output descriptions and example problems. The input is described in detail including (1) geometry modeling, (2) types of finite elements, (3) types of analysis, (4) material data, (5) types of loading, (6) boundary conditions, (7) output control, (8) program options, and (9) data bank.

Lackney, J. J.↗

DOE OSTI2015

International Round-Robin Study on Thermoelectric Transport Properties of n-type Half-Heusler from 300 K to 773 K

International transport property measurement round-robins have been conducted by the Thermoelectric Annex under the International Energy Agency (IEA) Implementing Agreement on Advanced Materials for Transportation (AMT). The previous round-robins used commercially available bismuth telluride as the testing material, with the goals of understanding measurement issues and developing standard testing procedures. The current round-robin extended the measurement temperature range to 773 K. It was designed to meet the increasing demands for reliable transport data of thermoelectric materials for power generation applications. Eleven laboratories from six IEA-AMT member countries participated in this study. Half-Heusler (n-type) material prepared by GMZ Energy was selected for the round-robin. The measured transport properties showed narrower distribution on uncertainties compared to previous round-robin efforts. The study intentionally included multiple testing methods and instrument types. Over the full temperature range, the measurement discrepancies on the figure of merit, ZT, in this round-robin were ±1.5 to ±16.4% from the averages.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Polarity governs atomic interaction through two-dimensional materials

The objective of this project is to develop two-dimensional material-based layer transfer (2DLT) for high-efficiency, low-cost III-V solar cells. More specifically, in short term, the team will develop 2DLT for cost-cost, high-throughput GaAs single-junction solar cells. The team will develop ultraclean high yield graphene transfer on GaAs and optimize the remote homoepitaxy process to obtain dislocation-free single-crystalline GaAs on graphene whose crystalline quality is identical to that of the GaAs wafer [1,2]. The team will develop the 2DLT process for a solar cell with highest achievable efficiency. The team will also strive to target GaAs solar cells with efficiency of 25~29% before and after the transfer, and reuse the substrate multiple times without CMP by damage-free transfer process enabled by 2DLT. Our team is partnered with industrial collaborators to obtain World record efficiency of flexible GaAs solar cells. Once the concept is fully realized for the GaAs solar cells, the team will expand the concept for multiple-junction solar cell targeting 35% efficiency with the 2DLT process in other projects.

36 MATERIALS SCIENCE↗