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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Structural, electronic, vibrational, and elastic properties of graphene/ MoS 2 bilayer heterostructures

Graphene/MoS 2 van der Waals (vdW) heterostructures have promising technological applications due to their unique properties and functionalities. Many experimental and theoretical research groups across the globe have made outstanding contributions to benchmark the properties of graphene/MoS 2 heterostructures. Even though some research groups have modeled the graphene/MoS 2 heterostructures using first-principles calculations, there exist several discrepancies in the results from different theoretical research groups and the experimental findings. In the present work, we revisit this problem by means of first-principles calculations and address the existing discrepancies about the interlayer spacing between graphene and MoS 2 monolayers in graphene/MoS 2 heterostructures and about the location of Dirac points near the Fermi level. We further investigate the electronic, mechanical, and vibrational properties of the optimized graphene/MoS 2 heterostructures created using 5 x 5/4 x 4 and 4 x 4/3 x 3 supercell geometries having different magnitudes of lattice mismatch. The effect of the varying interlayer spacing on the electronic properties of heterostructures is discussed. Our phonon calculations reveal that the interlayer shear and breathing phonon modes, which are very sensitive to the weak vdW interactions, play a vital role in describing the thermal properties of the studied systems. The thermodynamic and elastic properties of heterostructures are further discussed. A systematic comparison between our results and the results reported from other research groups is presented.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Building Structure-Property Relationships of Cycloalkanes in Support of Their Use in Sustainable Aviation Fuels

In 2018 13.7 EJ of fuel were consumed by the global commercial aviation industry. Worldwide, demand will increase into the foreseeable future. Developing Sustainable Aviation Fuels (SAFs), with decreased CO 2 and soot emissions, will be pivotal to the on-going mitigation efforts against global warming. Minimizing aromatics in aviation fuel is desirable because of the high propensity of aromatics to produce soot during combustion. Because aromatics cause o-rings to swell, they are important for maintaining engine seals, and must be present in at least 8 vol% under ASTM-D7566. Recently, cycloalkanes have been shown to exhibit some o-ring swelling behavior, possibly making them an attractive substitute to decrease the aromatic content of aviation fuel. Cycloalkanes must meet specifications for a number of other physical properties to be compatible with jet fuel, and these properties can vary greatly with the cycloalkane chemical structure, making their selection difficult. Building a database of structure-property relationships (SPR) for cycloalkanes greatly facilitates their furthered inclusion into aviation fuels. The work presented in this paper develops SPRs by building a data set that includes physical properties important to the aviation industry. The physical properties considered are energy density, specific energy, melting point, density, flashpoint, the Hansen solubility parameter, and the yield sooting index (YSI). Further, our data set includes cycloalkanes drawn from the following structural groups: fused cycloalkanes, n-alkylcycloalkanes, branched cycloalkanes, multiple substituted cycloalkanes, and cycloalkanes with different ring sizes. In addition, a select number of cycloalkanes are blended into Jet-A fuel (POSF-10325) at 10 and 30 wt%. Comparison of neat and blended physical properties are presented. One major finding is that ring expanded systems, those with more than six carbons, have excellent potential for inclusion in SAFs. Our data also indicate that polysubstituted cycloalkanes have higher YSI values.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Process-Dependent Properties in Colloidally Synthesized “Giant” Core/Shell Nanocrystal Quantum Dots

Due to their characteristic bright and stable photoluminescence, semiconductor nanocrystal quantum dots (NQDs) have attracted much interest as efficient light emitters for applications from single-particle tracking to solid-state lighting. Despite their numerous enabling traits, however, NQD optical properties are frustratingly sensitive to their chemical environment, exhibit fluorescence intermittency ('blinking'), and are susceptible to Auger recombination, an efficient nonradiative decay process. Previously, we showed for the first time that colloidal CdSe/CdS core/shell nanocrystal quantum dots (NQDs) comprising ultrathick shells (number of shell monolayers, n, > 10) grown by protracted successive ionic layer adsorption and reaction (SILAR) leads to remarkable photostability and significantly suppressed blinking behavior as a function of increasing shell thickness. We have also shown that these so-called 'giant' NQDs (g-NQDs) afford nearly complete suppression of non-radiative Auger recombination, revealed in our studies as long biexciton lifetimes and efficient multiexciton emission. The unique behavior of this core/shell system prompted us to assess correlations between specific physicochemical properties - beyond shell thickness - and functionality. Here, we demonstrate the ability of particle shape/faceting, crystalline phase, and core size to determine ensemble and single-particle optical properties (quantum yield/brightness, blinking, radiative lifetimes). Significantly, we show how reaction process parameters (surface-stabilizing ligands, ligand:NQD ratio, choice of 'inert' solvent, and modifications to the SILAR method itself) can be tuned to modify these function-dictating NQD physical properties, ultimately leading to an optimized synthetic approach that results in the complete suppression of blinking. We find that the resulting 'guiding principles' can be applied to other NQD compositions, allowing us to achieve non-blinking behavior in the near-infrared. Lastly, in addition to realizing novel light-emission properties by refining nanoscale architectures at the single-NQD level, we also investigate collective properties by assembling our core/shell NQDs into larger scale arrays.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Syntheses, crystal structures and properties of two unusual pillared-layer 3d-4f Ln-Cu heterometallic coordination polymers

Two unusual pillared-layer 3d-4f Ln-Cu heterometallic coordination polymers, {l_brace}[Ln{sub 2}Cu{sub 5}Br{sub 4}(IN){sub 7}(H{sub 2}O){sub 6}].H{sub 2}O{r_brace}{sub n} (Ln=Eu (1) and Gd (2), HIN=isonicotinic acid), have been synthesized under hydrothermal conditions, and characterized by elemental analysis, IR, thermal analysis and single-crystal X-ray diffraction. The structure determination reveals that 1 and 2 are isostructural and feature a novel three-dimensional pillared-layer hetrometallic structure built upon the linkages of one-dimensional (1D) linear Ln-carboxylate chains, zero-dimensional (0D) Ln-carboxylate Ln{sub 2}(IN){sub 8} dimers, rare 1D zigzag [Cu{sub 5}Br{sub 4}]{sub n} inorganic chains and IN{sup -} pillars. In both 3D structures, there are Ln-carboxylate layers resulted from the connections of 1D Ln-carboxylate chains and 0D Ln{sub 2}(IN){sub 8} dimers through O-H...O hydrogen bondings. The luminescent properties of 1 have been investigated. The magnetic properties of 1 and 2 have also been studied. - Graphical abstract: Two unusual pillared-layer Eu (Gd)-Cu heterometallic coordination polymers have been hydrothermally synthesized. The luminescent properties of Eu-Cu compound and magnetic properties of both compounds are investigated. Highlights: > Two unusual 3D pillared-layer Eu (Gd)-Cu heterometallic coordination polymers have been synthesized. > 1D and 0D Ln-carboxylate motifs construct layers by O-H...O hydrogen bondings. > In both the structures, there are rare 1D zigzag Cu/Br inorganic chains. > Luminescent properties of Eu-Cu compound and magnetic properties of both the compounds are investigated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Hybrid Monomer Design Synergizing Property Trade‐offs in Developing Polymers for Circularity and Performance

Abstract Current search for more sustainable plastics seeks to redesign polymers possessing both chemical recyclability to monomer for a circular plastics economy and desirable performance that can rival or even exceed today's non‐recyclable or hard‐to‐recycle petroleum‐based incumbents. However, within a traditional monomer framework it is challenging to optimize, concurrently , contrasting polymerizability/depolymerizability and recyclability/performance properties. Here, we highlight the emerging hybrid monomer design strategy to develop intrinsically circular polymers with tunable performance properties, aiming to unify desired, but otherwise conflicting, properties in a single monomer. Conceptually, this design hybridizes parent monomer pairs of contrasting, mismatching, or matching properties into offspring monomers that not only unify the above‐described conflicting properties but also radically alter the resultant polymer properties far beyond the limits of what either parent homopolymers or their copolymers can achieve.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Structural, Magnetic, and Optoelectronic Properties of CuMnSe{sub 2}-Chalcopyrite: DFT + U and Hybrid Functional Investigation

The work presented in this manuscript is a study of structural, magnetic, and optoelectronic properties of CuMnSe{sub 2}-chalcopyrite by FP-(L)APW + lo method using semilocal and hybrid functional. Structural properties such as cell parameters, bulk modulus, and its pressure derivative, as well as the cohesive energy and total energy of the unit cell were determined for the three magnetic phases (AFM, FM, and NM) from which it has been found that CuMnSe{sub 2}-chalcopyrite is ferromagnetic. The studied elastic properties confirm the mechanical stability of CuMnSe{sub 2} in its chalcopyrite structure. Electronic properties, such as the band gap energy, density of states, and charge density, and magnetic properties, such as Hubbard term estimation, magnetic moment, and polarization of the CuMnSe{sub 2}, have been predicted by several methods (GGA-PBEsol + U{sub eff}, GGA-PBEsol-(mBJ) + U{sub eff}, and hybrid functional). Optical properties such as the analysis of the dielectric function and the prediction of the refractive index and birefringence variations were also studied.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Full-Field Strain Measurement Integrated with Two Dimension Regression Analysis to Evaluate the Bi-Modulus Elastic Properties of Isotropic and Transversely Isotropic Materials

Background: Measuring the physical properties of shale is critical for optimizing engineering activities such as geothermal energy generation and hydraulic fracturing. Shale is a transversely isotropic material. Furthermore, this material can also include micro and macro cracks at different locations and orientations that cause it to behave differently under tensile or compressive loading. Objective: In this work, a combined experimental–numerical approach is proposed to evaluate the bi-modulus elastic properties of isotropic and transversely isotropic materials. Methods: Full-field strain measurements for a circular disk under diametral compression are integrated with a regression analysis technique to evaluate the elastic properties of bi-modulus materials subjected to tensile and compressive loads using two loading configurations on the same specimen. Digital Image Correlation (DIC) is used to measure the full-field strains. Subsequently, in the case of an isotropic material, a linear least-squares approach is utilized to process the experimentally determined strains in conjunction with analytical expressions of the stress fields (in terms of far-field loading) to determine the elastic modulus E, the shear modulus G, and the Poisson’s ratio $v$. In the case of a transversely isotopic material, such as shale, a finite element model is implemented to determine the stress fields (again in terms of far-field loading), which is followed by repeating the previous regression analysis in an iterative process to estimate the elastic parameters. Results: The results show that the proposed technique successfully provides a complete set of elastic properties as a function of both the loading condition and the principal material directions. The technique is validated by measurements on a known isotropic material and then applied to determine the properties of shale. Conclusion: In this work, the proposed approach is successfully used to calculate the bi-modulus elastic response of poly(methyl meth- acrylate) (PMMA) and shale. As expected, PMMA exhibits an isotropic response with no bi-modulus effect, however, shale exhibits both transverse isotropy and a bi-modulus effect. Therefore, this approach holds promise for investigating the elastic properties of materials like rocks and fiber-reinforced composite laminates as functions of the principal material directions and the loading conditions.

42 ENGINEERING↗
DOE OSTI2019

Processing and Thermoelectric Properties of TiNiSn Materials: A Review

The half-Heusler alloy TiNiSn is a promising material for high-temperature thermoelectric applications due to its good thermal stability and semiconductor-like electrical properties. Numerous synthesis techniques have been utilized to make TiNiSn, but a comparative study on its thermoelectric properties with respect to processing parameters has not been reported. Based on published experimental data, primary melting methods, such as arc melting or induction levitation melting, do not have a noticeable effect on the final thermoelectric properties, although choice of densification technique and annealing parameters correlate with each thermoelectric property. Thermal conductivity (2.47-6.08 W/m K), governed by lattice scattering effects, was maximized with high density from the spark plasma sintering (SPS) technique as well with low inclusions of metallic impurities and interstitial Ni defects from low-temperature, non-densified processes. Electrical resistivity (4.75-30 µΩ m), inversely related to thermal conductivity, is minimized when density is maximized and chemical defects are favorable from using SPS. All reported TiNiSn alloys contain intermetallic impurities, imparting a global trend of lowered electrical resistivity. Seebeck coefficient (− 273.20 to − 50.71 µV/K), proportional to electrical resistivity, is maximized when charge carrier concentration is minimized by eliminating phase impurities and Ni defects. Porosity has been observed to scatter low-energy electrons, which can increase Seebeck coefficient and electrical resistivity, although no statistical significance is found. An ideal TiNiSn alloy should have intermediate values of all interconnected thermoelectric properties to maximize ZT. Future research work should strive to include quantitative phase analysis to better characterize the contributions of Ni defects and impurity phases toward thermoelectric properties.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Understanding fundamental effects of biofuel structure on ignition and physical fuel properties

The development of biochemicals and biofuels with advantaged properties of higher combustion efficiency at lower emission levels can be aided by a priori prediction of critical global characteristics based on molecular structure. Existing predictive techniques are incomplete for comprehensive ignition and physical fuel property prediction. Here this investigation focuses on filling this knowledge gap by developing a priori prediction techniques for predicting important ignition as well as physical fuel properties of promising advantaged biofuels. We demonstrate the utility of this a priori prediction technique on saturated (≤C 5 ) alcohols, both linear and branched in nature by correlating their molecular structure with both important ignition and physical properties of the fuels. This work utilizes a semi-automated method of predicting ignition characteristics via accurate fundamental-based calculations of the fuel radical cascades that govern low-temperature combustion. This numerical methodology is supported by the relevant fuel ignition delay time (IDT) and research octane number (RON) data experimentally measured by the Advanced Fuel Ignition Delay Analyzer (AFIDA). Phyiscal fuel property trends are also analyzed by correlating the molecular structure of the fuel to its physical characteristics. Based on their molecular structure, recommendations are made on an a priori method for selecting biofuels that have advantaged properties for the selected fuel application. Lastly, the utility of this investigation is extended beyond the subset of alcohols considered by analyzing the IDT trends of i-Pentanol and n-Hexanol, revealing the fidelity of the novel kinetic modelling approach and the accuracy of the predicted trends in this study.

09 BIOMASS FUELS↗
DOE OSTI2022

Modulation of apparent optical properties using arrayed mesoscale structures

In this study, a method for using arrays of mesoscale structures to modify the apparent optical properties of an opaque composite surface has been theoretically demonstrated to both raise and lower the apparent emissivity as compared to the intrinsic properties of the constitutive materials. For design problems where thermomechanical and optical material properties are both of importance, mesoscale surface structuring can greatly expand the design space. Analysis via the net radiosity method herein illustrates the ability to achieve a wide range of spectral apparent optical properties. Notably, a hexagonal array of spheres on a planar surface can raise the apparent emissivity of a planar surface by 50%. Conversely, a hexagonal enclosure of reradiating surfaces, realized by thin adiabatic walls, can reduce the apparent emissivity of a blackbody by half. As this method of modifying apparent optical properties utilizes structures much larger than the wavelengths of interest, the relationship between intrinsic planar emissivity, geometry, and apparent emissivity can be computed semi-analytically at low computational expense. Passive solar cooling, thermophotovoltaic cells, aerodynamic surfaces exposed to intense heating, and solar absorbers are presented as case studies that could benefit from the use of mesoscale structures on opaque surfaces to modify the apparent optical properties.

42 ENGINEERING↗
DOE OSTI2014

Density functional theory investigation of the electronic structure and thermoelectric properties of layered MoS{sub 2}, MoSe{sub 2} and their mixed-layer compound

First principles density functional theory calculations were carried out for the 2H-MoQ{sub 2} (Q=S and Se) and their hypothetical mixed-layer compound. Due to the different electronegativities of S and Se atoms on MoQ{sub 2}, the band gap size could be adjusted in mixed-layer compound MoS{sub 2}/MoSe{sub 2}. Also, the indirect band gap in pure MoQ{sub 2} compounds is changed to the pseudo direct band gap in mixed-layer MoS{sub 2}/MoSe{sub 2} which is similar to the monolayer compound. The layer mixing enhances the thermoelectric properties because of the increased density of states around the Fermi level and the decreased band gap size. Therefore, we suggest that this layer mixing approach should be regarded as a useful way to modulate their electronic structures and to improve their thermoelectric properties. -- Graphical abstract: On the basis of density functional calculations we predict that the mixed-layer compounds 2H-MoS{sub 2}/2H-MoSe{sub 2}, in which two different layers 2H-MoS{sub 2} and 2H-MoSe{sub 2}, have enhanced thermoelectric properties because of the increased density of states around the Fermi level and the decreased band gap size. Highlights: • We explored a way of improving TE properties of 2H-MoQ{sub 2} on DFT methods. • The mixed-layer compounds MoS{sub 2}/MoSe{sub 2} have enhanced thermoelectric properties. • This is caused by modulated electronic structure of mixed layer compound. • Layer mixing approach should be regarded as a useful way to improve TE properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Assembly and property research on seven 0D–3D complexes derived from imidazole dicarboxylate and 1,2-bi(pyridin-4-yl)ethene

The hydrothermal reaction of transition metals, 1H-imidazole-4,5-dicarboxylic acid (H{sub 3}ImDC) and 1,2-bi(pyridin-4-yl)ethene (bpe) affords a series of new complexes, namely, [Mn(HImDC)(bpe)(H{sub 2}O)] (1), [M(H{sub 2}ImDC){sub 2}(H{sub 2}O){sub 2}]·(bpe) (M=Fe(2), Co(3), Zn(4), Cd(6)), [Zn{sub 3}(ImDC){sub 2}(bpe)(H{sub 2}O)]·3H{sub 2}O (5) and [Cd(H{sub 2}ImDC)(bpe)] (7), which are characterized by elemental analyses, IR, TG, XRPD and single crystal X-ray diffraction. Complex 1 exhibits a one dimensional (1D) zigzag chain with two types of irregular rings, and the 1D chains are linked to form a three dimensional (3D) supramolecular framework by the hydrogen bonding interactions (O–H∙∙∙O and O–H∙∙∙N). Complexes 2–4 and 6 are isomorphous, and they display the mononuclear structures. In these complexes, the O–H∙∙∙O and O–H∙∙∙N hydrogen bonds play an important role in sustaining the whole 3D supramolecular frameworks. Complex 5 shows a (3,3)-connected 3D framework with (10{sup 3}) topology, and the lattice water molecules as guest molecules exist in the 3D framework. Complex 7 is a wave-like two dimensional (2D) structure, in which the adjacent 1D chains point at the opposite directions. Moreover, the fluorescent properties of complexes 1–7 and the magnetic property of 1 have been investigated. The water vapor adsorption for complex 5 has been researched at 298 K. - Graphical abstract: Seven new complexes based on different structural characteristics have been hydrothermally synthesized by the mixed ligands. The fluorescent properties, the magnetic property and the water vapor adsorption have been investigated. - Highlights: • The semi-rigid ligand with C=C bonds and imidazole dicarboxylates with some advantages have been used. • A series of new complexes with different structural characteristics have been discussed in detail. • The fluorescent properties, the magnetic property and the water vapor adsorption have been investigated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Structural and electrical properties of Si- and Ti-doped Cu{sub 2}SnSe{sub 3} bulks

Silicon-doped (Cu{sub 2}(Sn{sub 1−x}Si{sub x})Se{sub 3} and titanium-doped (Cu{sub 2}(Sn{sub 1−x}Ti{sub x})Se{sub 3} at x=0, 0.05, 0.1, 0.15, and 0.2 were prepared at 550 °C for 2 h with soluble sintering aids of volatile Sb{sub 2}S{sub 3} and Te. Defect chemistry was studied by measuring structural and electrical properties of Si-doped and Ti-doped Cu{sub 2}SnSe{sub 3} (CTSe) as a function of dopant concentration. Si-doped CTSe pellets show p-type at x=0 and 0.05 and n-type at x=0.1, 0.15, and 0.2, whereas Ti-doped CTSe pellets show p-type at x=0, 0.05 and 0.1 and n-type at x=0.15 and 0.2. The lowest hole concentration of 3.6×10{sup 17} cm{sup −3} and the highest mobility of 1525 cm{sup 2} V{sup −1} s{sup −1} were obtained for the Si-doped (Cu{sub 2}(Sn{sub 1−x}Si{sub x})Se{sub 3} bulks at x=0.1 (10% Si), while they were 3.1×10{sup 17} cm{sup −3} and 813 cm{sup 2} V{sup −1} s{sup −1} for the Ti-doped CTSe bulks at x=0.15 (15% Ti), as compared to 1.1×10{sup 18} cm{sup −3} and 209 cm{sup 2} V{sup −1} s{sup −1} for undoped one. The explanations based upon antisite defects of Si-to-Sn, Ti-to-Sn, Cu-to-Sn, and Sn-to-Cu for the changes in electrical property were declared. The study in bulk Si-doped and Ti-doped CTSe is based upon defect state and is consistent and supported by the data of electrical property and lattice parameter. - Graphical abstract: Cu{sub 2}SnSe{sub 3} (CTSe) semiconductor is interesting because of its adjustable electrical properties by extrinsic doping. Si and Ti doping in CTSe leads to high carrier mobility above 800 cm{sup 2} V{sup −1} s{sup −1}. - Highlights: • Cu{sub 2}SnSe{sub 3} (CTSe) is an interesting semiconductor because of its adjustable electrical properties. • Cu(In,Ga)Se{sub 2}, on the contrary, is difficult to change its electrical properties. • Si and Ti doping can change p-CTSe to n-CTSe. • The lowest electron concentration in doped CTSe had the highest mobility above 800 cm{sup 2} V{sup −1} s{sup −1}. • The defects of Si-to-Sn, Ti-to-Sn, Cu-to-Sn, and Sn-to-Cu in Si- and Ti-doped CTSe were proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structural and thermoelectric properties of zintl-phase CaLiPn (Pn=As, Sb, Bi)

First-principles calculations were carried out to study the structural, mechanical, dynamical and transport properties of zintl phase materials CaLiPn (Pn=As, Sb and Bi). We have used two different approaches to solve the system based on density functional theory. The plane wave pseudopotential approach has been used to study the structural and dynamical properties whereas, full potential linear augment plane wave method is used to examine the electronic structure, mechanical and thermoelectric properties. The calculated ground-state properties agree quite well with experimental values. The computed electronic structure shows the investigated compounds to be direct band gap semiconductors. Further, we have calculated the thermoelectric properties of all the investigated compounds for both the carriers at various temperatures. We found a high thermopower for both the carriers, especially n-type doping to be more favourable, which enabled us to predict that CaLiPn might have promising applications as a good thermoelectric material. Further, the phonon dispersion curves of the investigated compounds showed flat phonon modes and we also find lower optical and acoustic modes to cut each other at the lower frequency range, which further indicate the investigated compounds to possess reasonably low thermal conductivity. We have also analysed the low value of the thermal conductivity through the empirical relations and discussions are presented here. - Highlights: • Electronic band structure and chemical bonding. • Single crystalline elastic constants and poly crystalline elastic moduli. • Thermoelectric properties of zintl phase. • Lattice dynamics and phonon density of states.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The effect of a prior short-term ageing on mechanical and creep properties of P92 steel

Highlights: • The results of simulated ageing at 650°C allows to estimate degradation of P92 steam pipes due to accidental overheating. • Simulated ageing has only a slight effect on ambient tensile properties and hardness. • A sudden decrease in impact properties occurred after ageing for 2000h. The FATT of about 25°C was determined. • The creep results show a clear detrimental influence of tempering ageing on the creep strength. • No Z-phase precipitation occurred due to the ageing process. - Abstract: We have investigated the effect of prior short-term ageing on the mechanical and creep properties of tungsten and boron modified 9%Cr ferritic steel (ASTM Grade P92 steel), to provide material data base for the estimation of material degradation due to occurrence of accidental overheating in the early stage of service loading. The steel was aged at 650 °C for up to 100, 200, 500, 1000, 2000 and 5000 h prior to mechanical and creep testing. Changes in the microstructure during ageing had a slight effect on the reduction of room temperature tensile properties. A sudden decrease on impact properties occurred after ageing for 2000 h, but the occurred impact energy of about 70 J is in accordance with the specified minimum value of 68 J at room temperature for the virgin condition. The creep behaviour of P92 steel in the as-received condition and after different isothermal ageing exposures prior to creep was investigated at 600 and 650 °C in the power-law creep regime. The initial applied tensile stress ranged from 90 to 200 MPa. The results clearly show a detrimental influence of isothermal ageing on creep properties even after a few hundred hours. Based on microstructure analysis, which was done mostly in a qualitative way, a significant decrease in the creep life after ageing resulted from changes of the dislocation substructure and instability of Laves phase and M{sub 23}C{sub 6} particles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Systematic DFT study of the impact of anionic variations on the physical properties of Cd1-xMnxX (XS, Se, Te; x = 6.25%)

Highlights: • The structural and electronic properties are investigated with most accurate mBJ potential. • The FM state stability is illustrated for Cd{sub 0.9375}Mn{sub 0.0625}S/Se/Te DMSs. • The FM semiconducting nature depicts potential applications in magneto-optic applications. • The absorption shifts within the visible range with S to Te variation that is verified by E{sub g}. • Thermoelectric properties indicate dominant hole-carriers and suitability at high temperatures. - Abstract: The structural and electronic properties are theoretically investigated for Cd{sub 1-x}Mn{sub x}X (XS, Se, Te; x = 6.25%) diluted magnetic semiconductors, which are further employed for extracting the magnetic, optical and thermoelectric properties using modified-Becke-Johnson (mBJ) potential. Ferromagnetic state stability is confirmed through the computed enthalpy of formation and the cohesive energies. The electronic properties elucidate Cd{sub 1-x}Mn{sub x}X (XS, Se, Te; x = 6.25%) as ferromagnetic semiconductors because both spin channels have Fermi energy level (E{sub F}) within the band gap, depicting potential applications in spintronic devices. The calculated optical response indicates shifts in the absorption within the visible energy that is consistent with the computed direct band gap values (1.9 eV–3.1 eV). Thermoelectric properties observed within 200 K–800 K show positive Seebeck coefficient indicating holes as majority charge carriers. Although Mn-doping suppresses the power factor, however, it improves with temperature, showing a potential for optimizing the thermoelectric performance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Mechanical and tribological properties of anodic Al coatings as a function of anodizing conditions

Enhanced wear and corrosion resistance properties are vital for numerous functional and decorative applications. Anodizing is a process frequently used to generate stable oxide coatings on metal surfaces, including aluminium (Al). In this work, we present an evaluation of process variables for optimized anodized coating properties using existing methods and as a baseline for novel coating development. A representative relatively pure Al alloy was chosen as a model system with a goal of finding conditions to achieve high wear coatings with retained ductility. AA5052 alloy coupons were anodized in two different electrolytes (sulfuric and phosphoric acid) to study the effects of anodizing conditions on the mechanical and tribological properties of the anodic coatings. Porosity was evaluated with microscopy, coating hardness was determined via nanoindentation, and tribological properties were characterized using a pin-on-disk tribometer. These measurements were correlated and a loading evaluation was performed to assess the optimum nanoindentation parameters for the use of representative coupons without the need for special processing prior to anodizing. The porosity and coating thickness were found to depend on the anodizing time and the type of electrolyte. Thicker and harder anodic coatings were generated in sulfuric acid compared to phosphoric acid. Porosity studies of the anodic coatings generated in phosphoric acid revealed that coating porosity decreased as the anodizing time increased. Both electrolytes generated anodic coatings with improved tribological properties (friction coefficient and dimensional wear rate), and an optimum processing time was identified for best wear properties.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Origin of Electrical Property Deterioration with Increasing Mg Concentration in ZnMgO:Ga

Transparent conductive Ga-doped Zn{sub 1-x}Mg{sub x}O (ZnMgO:Ga) films were epitaxially grown via Pulsed Laser Deposition on sapphire by optimizing the substrate temperature and other parameters of deposition. Zn{sub 0.68}Mg{sub 0.31}Ga{sub 0.01}O/sapphire films deposited at 400 C have a Hall mobility ({mu}) of 9.2 {+-} 0.5 cm{sup 2} V{sup -1} s{sup -1} and a free electron density (n) of 1.79 x 10{sup 20} {+-} 0.06 x 10{sup 20} cm{sup -3}, yielding an electrical conductivity ({sigma}) = 262 {+-} 22 S/cm. Zn{sub 0.90}Mg{sub 0.09}Ga{sub 0.01}O/sapphire films, deposited under the same growth conditions, have similar crystalline quality, but significantly better electrical properties ({sigma} = 1450 {+-} 10 S/cm, {mu} = 24.5 {+-} 2.5 cm{sup 2} V{sup -1} s{sup -1}, n = 3.81 x 10{sup 20} {+-} 0.20 x 10{sup 20} cm{sup -3}). This comparison provides evidence of electrical property deterioration in doped ZnMgO bulk material with increasing Mg content, independent of crystalline quality. Electrical properties of ZnMgO:Ga are further deteriorated by the decrease of the crystalline quality. Polycrystalline Zn{sub 0.90}Mg{sub 0.09}Ga{sub 0.01}O/a-SiO{sub 2} samples deposited under identical conditions on amorphous silica substrates had both inferior crystal quality and inferior transport properties ({mu} = 2.5 {+-} 0.2 cm{sup 2} V{sup -1} s{sup -1}, n = 2.04 x 10{sup 20} {+-} 0.20 x 10{sup 20} cm{sup -3}, {sigma} = 80 {+-} 8 S/cm) compared to their epitaxial counterparts. Overall, the results of this study indicate that both bulk material properties and crystalline quality influence the electrical properties of single-phase ZnMgO:Ga thin films.

14 SOLAR ENERGY↗