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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

The ENSO-Australian rainfall teleconnection in reanalysis and CMIP5

Australian rainfall is strongly influenced by the El Niño-Southern Oscillation (ENSO). The relationship between ENSO and rainfall in eastern Australia is non-linear; the magnitude of La Niña events has a greater effect on rainfall than does the magnitude of El Niño events, and the cause of the non-linearity is unclear from previous work. The twentieth century reanalysis succeeds in capturing the asymmetric ENSO-rainfall relationship. In the reanalysis the asymmetry is strongly related to moisture availability in the south-west Pacific whereas wind flow is of less importance. Some global climate models (GCMs) in the CMIP5 archive capture the asymmetric nature of the ENSO-rainfall relationship whilst others do not. Differences in thermodynamic processes and their relationships with ENSO are the primary cause of variability in model performance. Analysis of an atmosphere-only run of a GCM which fails to capture the non-linear ENSO-rainfall relationship is also conducted. The atmospheric run forced by observed SSTs shows no significant improvement in the ENSO-rainfall relationship over the corresponding coupled model run in the CMIP5 archive. This result suggests that some models are failing to capture the atmospheric teleconnection between the tropical Pacific and Australia, and both this and a realistic representation of oceanic ENSO characteristics are required for coupled models to accurately capture the ENSO-rainfall teleconnection. These findings have implications for the study of rainfall projections in the region.

Meteorology & Atmospheric Sciences↗
DOE OSTI2022

TOUGH3-FLAC3D: a modeling approach for parallel computing of fluid flow and geomechanics

The recent development of the TOUGH3 code allows for a faster and more reliable fluid flow simulator. At the same time, new versions of FLAC3D are released periodically, allowing for new features and faster execution. In this paper, we present the first implementation of the coupling between TOUGH3 and FLAC3Dv6/7, maintaining parallel computing capabilities for the coupled fluid flow and geomechanical codes. We compare the newly developed version with analytical solutions and with the previous approach, and provide some performance analysis on different meshes and varying the number of running processors. Finally, we present two case studies related to fault reactivation during CO 2 sequestration and nuclear waste disposal. The use of parallel computing allows for meshes with a larger number of elements, and hence more detailed understanding of thermo-hydro-mechanical processes occurring at depth.

58 GEOSCIENCES↗
DOE OSTI2019

A Kinetic Model for Dissolution of Zinc Oxide Powder Obtained from Waste Alkaline Batteries in Sodium Hydroxide Solutions

The determination of individual dissolution behaviors of zinc and manganese in waste alkaline battery powders is an important subject from the points of the leaching yield, design of leaching reactor, and separation and recovery steps of hydrometallurgical process. In the current study, we investigated the dissolution kinetics of zinc oxide powder. Zinc oxide was obtained from waste alkaline batteries, and sodium hydroxide solutions were used as solvent. In the experiments, the effects of solution concentration, reaction temperature, stirring speed, solid-to-liquid ratio, and particle size on the dissolution of zinc oxide were investigated. It was demonstrated that the dissolution increased with the increasing concentration, reaction temperature, and stirring speed, and with the decreasing solid-to-liquid ratio and particle size. In consequence of the kinetic analysis performed, it was found that the dissolution kinetics of zinc powder obeyed the Avrami model. Activation energy for the process was determined to be 19.42 kJ/mol. Zinc ions in the resulting solution after dissolution process was recovered in the form of hydroxy-carbonate product by precipitation method. Zinc oxide was produced by isothermal decomposition of hydroxy-carbonate product.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Exploring the Short-Channel Characteristics of Asymmetric Junctionless Double-Gate Silicon-on-Nothing MOSFET

This paper presents an analytical model of an asymmetric junctionless double-gate (asymmetric DGJL) silicon-on-nothing metal-oxide-semiconductor field-effect transistor (MOSFET). Solving the 2-D Poisson’s equation, the expressions for center potential and threshold voltage are calculated. In addition, the response of the device toward the various short-channel effects like hot carrier effect, drain-induced barrier lowering and threshold voltage roll-off has also been examined along with subthreshold swing and drain current characteristics. Performance analysis of the present model is also demonstrated by comparing its short-channel behavior with conventional DGJL MOSFET. The effect of variation of the device features due to the variation of device parameters is also studied. The simulated results obtained using 2D device simulator, namely ATLAS, are in good agreement with the analytical results, hence validating our derived model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Monte Carlo fuel burnup analyses of the Accelerator-Driven Subcritical systems

Here, we discuss the Monte Carlo fuel burnup analysis performed for the Argonne National Laboratory (ANL) Accelerator-Driven Subcritical (ADS) conceptual design. The ANL ADS conceptual design was determined to dispose of the 131 tons of Minor Actinides (MA) fuel of the current United States Spent Nuclear Fuel (SNF) inventory. It uses a neutron source from 1 GeV 25MW proton beam with the liquid lead target to drive the subcritical fission assembly. It utilizes the liquid metal slurry fuel concept to load the MAs fuel. The subcritical fission assembly has a neutron multiplication factor of 0.98. The total fission power generated in the system is about 2.67 GW. The system is designed to operate for 35 full power years. Monte Carlo fuel burnup analyses were performed to calculate the amount of MAs consumed by the ANL ADS conceptual design. The MCNP6 computer program was used to simulate the high energy physics of the protons striking the liquid lead target for generating the neutron source. The MCB5 and SERPENT Monte Carlo burnup computer programs were used to simulate the fuel burnup during the ADS operation. In the ANL ADS conceptual configuration, the reactivity loss during the fuel burnup is compensated by adding fresh fuel into the subcritical assembly. In this paper, both batch and continuous fueling modes are examined. The fresh fuel particles are loaded into the slurry fuel carrier at the beginning of each burnup step of the batch-fueling mode and loaded continuously into the slurry fuel carrier during the operation in the continuous fueling mode. Monte Carlo fuel burnup analyses show that one ANL ADS conceptual design can consume about 25.7 tons of MAs fuel during the 35 full power years with the continuous fueling mode. About five units is required to dispose of the 131 tons of MAs

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

A review of microgrid development in the United States – A decade of progress on policies, demonstrations, controls, and software tools

Microgrids have become increasingly popular in the United States. Supported by favorable federal and local policies, microgrid projects can provide greater energy stability and resilience within a project site or community. Here, we review major federal, state, and utility-level policies driving microgrid development in the United States. Representative U.S. demonstration projects are selected and their technical characteristics and non-technical features are introduced. The paper discusses trends in the technology development of microgrid systems as well as microgrid control methods and interactions within the electricity market. Software tools for microgrid design, planning, and performance analysis are illustrated with each tool's core capability. Finally, the paper summarizes the successes and lessons learned during the recent expansion of the U.S. microgrid industry that may serve as a reference for other countries developing their own microgrid industries.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2022

Quantitative evaluations of subtropical westerly jet simulations over East Asia based on multiple CMIP5 and CMIP6 GCMs

As a salient feature of the Asian monsoon system, the East Asian subtropical westerly jet (EASWJ) exerts significant impacts on weather and climate changes in China and even throughout East Asia. In this paper, we applied a new self-adaptive algorithm to detect the EASWJ, identify its boundaries, and then represent its characteristics by defining three indices: the intensity index, meridional displacement index, and width index. Compared to the reanalysis data, we carried out a comprehensive, objective, and quantitative EASWJ evaluation using historical experiments from multiple global climate models (GCMs) in the Coupled Model Intercomparison Project Phases 5 and 6 (CMIP5 and CMIP6). The results show that the multimodel ensemble mean (MME) of both CMIP5 and CMIP6 can simulate the characteristics of winter EASWJ well. While for the other three seasons, the MME of both phase models underestimate the 200-hPa zonal wind (U200) strength in the jet coverage area and overestimate the U200 outside the jet area, such simulation results weaken the meridional shear of the wind field. The EASWJ simulations from the CMIP5 GCMs had no consistent intensity or location characteristic tendencies, and most CMIP5 GCMs tended to simulate relatively wide-coverage jets. In contrast, most CMIP6 GCMs are inclined to simulate significantly weaker, wider, and more-northward jets. Compared to the predecessors in CMIP5, about half of CMIP6 GCMs significantly minimized the jet intensity bias, but remarkable errors were still observed in their jet location and coverage representations. Furthermore, the comparative analysis performed by classifying models based on their evaluated simulation results suggested that the simulated performance of the meridional temperature gradient was important for capturing the EASWJ characteristics. Further in-depth study of the causes of model differences is warranted to improve simulation results.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Sterol regulatory element-binding protein 1 inhibitors decrease pancreatic cancer cell viability and proliferation

Sterol regulatory element-binding protein1 (SREBP1) is a key regulatory factor that controls lipid homeostasis. Overactivation of SREBP1 and elevated lipid biogenesis are considered the major characteristics in malignancies of prostate cancer, endometrial cancer, and glioblastoma. However, the impact of SREBP1 activation in the progression of pancreatic cancer has not been explored. The present study examines the effect of suppression of SREBP1 activation by its inhibitors like fatostatin and PF429242 besides analyzing the impact of inhibitory effects on SREBP1 downstream signaling cascade such as fatty acid synthase (FAS), hydroxymethylglutaryl-CoA reductase (HMGCoAR), stearoyl-CoA desaturase-1 (SCD-1), and tumor suppressor protein p53 in MIA PaCa-2 pancreatic cancer cells. Both fatostatin and PF429242 inhibited the growth of MIA PaCa-2 cells in a time and concentration-dependent manner with maximal inhibition attained at 72 h time period with IC{sub 50} values of 14.5 μM and 24.5 μM respectively. Detailed Western blot analysis performed using fatostatin and PF429242 at 72 h time point led to significant decrease in the levels of the active form of SREBP1 and its downstream signaling proteins such as FAS, SCD-1 and HMGCoAR and the mutant form of tumor suppressor protein, p53, levels in comparison to the levels observed in vehicle treated control group of MIA PaCa-2 pancreatic cells over the same time period. Our in vitro data suggest that SREBP1 may contribute to pancreatic tumor growth and its inhibitors could be considered as a potential target in the management of pancreatic cancer cell proliferation. - Highlights: • A significant increase in SREBP1 levels was observed in MIA PaCa-2 cells. • Fatostatin and PF429242 suppress SREBP1 activation and its downstream signaling proteins expression. • The inhibition of SREBP1reduces tumor suppressor protein p53 in MIA PaCa-2 cells. • SREBP1 inhibition may be beneficial in treatment of pancreatic cancer.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Experimental validation of solid oxide fuel cell polarization modeling: An LSM-YSZ/YSZ/Ni-YSZ case study

Polarization modeling based on the measured I-V curves is a useful tool for analyzing SOFC performance and diagnosing performance limitations. Using the polarization model, the overpotential of a cell is usually separated into different polarization contributions, including area specific ohmic polarization, activation polarization, and anodic and cathodic concentration polarizations. In this study, we aim to experimentally validate the accuracy of the polarization model. As a case study, anode-supported cells with LSM-YSZ/YSZ/Ni-YSZ configuration are used. By curve-fitting the I-V curves of a cell tested under different cathode oxygen partial pressures into the polarization model, the contributions of different polarization losses are quantified. To validate the polarization model, independent experiments/studies including electrochemical impedance spectroscopy, cathode kinetics study, ex-situ diffusivity measurement, and tortuosity measurement using 3D reconstructed anode are conducted. The results from polarization modeling and from validation studies are in good agreement, thereby validating the polarization model for SOFC performance analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Epistemology of voltage control in DER-rich power system

Despite the recent development of several scalable, robust, and resilient control approaches with superior convergence properties considering an increasing penetration of distributed energy resources (DERs), cognitive oversights often simplify several aspects of the cyber–physical power system in the controller development. Here, following the identification of the limitations of classical controller definitions, we justify alternative definitions of voltage control approaches classifiers considering three inter-disciplinary domains: (i) power system, (ii) optimization and decision-making, and (iii) networking and cyber-security, to develop a taxonomy for helping in real-world comparative performance analysis and deployability of these controllers. We observe that classical and introduced domain-based definitions together can better classify the control algorithms.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

Genetic algorithm optimization of a chemical kinetic mechanism for propane at engine relevant conditions

Propane has demonstrated significant potential for reductions in greenhouse gas and pollutant emissions in medium- and heavy-duty engine applications, but further improvements require accurate, compact, and scalable chemical kinetic mechanisms to design the next generation of propane fueled engines, particularly at the boosted operating conditions necessary to meet the power density demand of medium- and heavy-duty applications. In this work, six key chemical reactions were identified in a reduced mechanism with 70 species and 352 reactions through a sensitivity analysis performed at conditions typical of thermodynamic trajectories observed in a high compression ratio, long stroke engine operated on propane from throttled to boosted operating conditions. While the original mechanism was validated against rapid compression machine (RCM) data, it was found to overpredict experimental autoignition tendencies in 2-zone, 0-D SI engine simulations performed in Chemkin Pro. Subsequently, a genetic algorithm approach was used to optimize the six reaction rate parameters within established uncertainty bounds by performing RCM simulations and comparing to two independent sets of literature ignition delay times for propane, thus generating two new kinetic mechanisms. The first optimization achieved a mean absolute percent error (MPE) reduction in 2nd stage ignition delay of 61.4% in seven generations, while the second optimization utilized a newer experimental RCM dataset, and achieved MPE reduction of 56.7% in seven generations, and further marginal improvement to 57.8% reduction in 34 generations. Finally, the two mechanisms were then evaluated again in the 2-zone 0-D SI engine model in Chemkin Pro comparing typical mean and knocking cycle trajectories, and it was found that the second optimized mechanism provided better prediction of knock onset at the representative conditions evaluated in this work, particularly for higher load operating conditions.

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

Architectural development of an ST fusion device

A recent U.S. National Academy study recommended the development of a next step Sustained High Power Density (SHPD) facility within the U.S. as an intermediate step in designing and building a Pilot Plant device. Several papers have been written describing the physics, design and engineering scoping analysis performed in developing this machine design. This paper places emphasis on the continued evolution of the architectural development of past activities to meet the requirements of an ST fusion pilot plant and power plant. The current effort centers on meeting basic physics and component requirements in a machine design that improves the chance of achieving fission level availability (95%) within an arrangement that promotes design simplicity, offsite construction with on-site modular assembly. As a prelude to both the SHPD and Pilot Plant, a scoping design of a 500MWe Spherical Tokamak Advanced Reactor (STAR) has been defined to investigate design options and physics scenarios that can successfully meet physics performance, engineering requirements and economic conditions of an ST power plant. Following a successful physics/engineering assessment, the STAR Power Plant design will be downsized to meet the specifications established in the design of a near term ST Pilot Plant

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Experimental investigation of the small-scale prototype of the dew point water recovery system

The article presents experimental investigation of the Dew Point Water Recovery (DPWR) system designed for clean water recovery using the dew point cooling phenomenon. The technology is a novel distillation process which allows for highly efficient water recovery. It is a first distillation technology which allows for water distillation through direct contact with atmospheric air. The authors designed, built, and tested an original prototype of a laboratory-scale DPWR system to verify its basic operating principles and perform performance analysis. It was shown that on average 10 × 10 −6 m 3 of clean water could be recovered from each cubic meter of the supply air with an average GOR of 1.9. Although the operation of the DPWR system requires electricity to drive fans, pumps and other associated equipment, the actual driving force of the system is thermal energy. The average thermal energy demand of the DPWR system was 370 kWh/m 3 , and more than half of this energy was based on the thermodynamic potential of the supply air. Based on experimental data, the mathematical model of the DPWR system was verified and it was found that the average relative discrepancy in predicting air temperature did not exceed 8%, and in predicting air humidity: 5%. In conclusion, the conducted experiments confirmed that the proposed DPWR system is feasible and has the potential to fill the technological gap in terms of a low-energy and easily accessible water recovery method.

42 ENGINEERING↗
DOE OSTI2021

ZrN coating as diffusion barrier in U(Mo) dispersion fuel systems

The control of the interaction between the U(Mo) fuel phase and the Al matrix is one of the challenges of dispersion fuel plate development for research reactors. Given the specific properties of this interaction layer, larger amounts of it in the meat could lead to a reduction of the plate mechanical integrity and thermal conductivity, eventually leading to pillowing. The SELENIUM project showed that by depositing a ZrN coating on the surface of the U(Mo) fuel particles, the amount of formed U(Mo)-Al interaction layer is limited but still present. Microstructural analysis performed on the as fabricated coating and fresh fuel plates containing ZrN coated U(Mo) dispersed in an Al matrix, revealed that the coating gets damaged during plate production. The post irradiation examinations (PIE) of the ZrN coated U(Mo) fuel plates, from the SELENIUM and SEMPER FIDELIS experiments, show how the U(Mo)-Al interaction layer is formed -only at those locations where the coating is missing or damaged -and the evolution of coating microstructure during irradiation. Finally, as a remedy, to further reduce the amount of interaction layer formed, the use of an Al-Si matrix was proposed based on the higher affinity of Si for U compared to the affinity of Al for U. PIE of a fuel plate consisting of ZrN coated U(Mo) dispersed in an Al-Si matrix irradiated in the SEMPER FIDELIS experiment, clearly demonstrates the benefit of adding Si to the matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Titanium porous-transport layers for PEM water electrolysis prepared by tape casting

While the porous-transport layer (PTL) is a key component in PEM electrolyzers, it is one of the most underexplored due to limited available structures. In this work, we present a novel PTL design for PEM water electrolyzers enabled by a cost-effective, scalable tape-casting technique. Here, a precise control of the PTL pore structure is achieved by incorporating poreformers of various sizes, and by varying the titanium and poreformer ratio. The structures are characterized with SEM and synchrotron X-ray computed tomography imaging techniques. Comprehensive electrochemical performance analysis demonstrates that higher titanium loading provides improved contact at the catalyst-layer/PTL interface but suffers from severe mass-transport losses due to gas bubbles. We solve this mass-transport problem by mixing in large poreformer beads that produce a highly porous structure with excellent gas removal properties yet still maintaining mechanical integrity. The PTL fabricated with 60:40 Ti:PMMA ratio and 60 μm PMMA bead size outperformed the standard commercial Ti powder-based PTL by 62 mV at 4 A/cm 2 .

25 ENERGY STORAGE↗
DOE OSTI2014

Magnetism and magnetocaloric effect in multicomponent Laves-phase compounds: Study and comparative analysis

This paper presents a review and results of comparative study of the influence of Gd on some physical properties of (R{sub 0.9}R′{sub 0.1}){sub 1−x}Gd{sub x}Co{sub 2} solid solutions with R=Dy, Ho and R′=Er, Ho and x varied from 0.05 to 0.15. Powder X-ray diffraction analysis performed at room temperature revealed that all studied solid solutions solidify with the formation of a Laves-phase MgCu{sub 2}-type structure (space group Fd−3m). The magnetization behavior and the magnetic transition are analyzed in terms of the Landau theory. The studies of magnetic properties and heat capacity showed that a relatively small Gd addition significantly increases T{sub C} of the compounds. The maximum percentage increase in T{sub C}, namely, ∼43% was observed for (Ho{sub 0.9}Er{sub 0.1}){sub 1−x}Gd{sub x}Co{sub 2}. However, the highest temperature was noted for the (Dy{sub 0.9}Ho{sub 0.1}){sub 0.85}Gd{sub 0.15}Co{sub 2} solid solution; it is T{sub C}=183.4 K. Below the ordering temperature, all samples are ferrimagnetically ordered; at high temperatures, they are Curie–Weiss paramagnets. Moreover, a small Gd addition eliminates the field-induced magnetic transition near T{sub C} and, as consequence, transforms the nature of magnetic transition from the first- to second-order. The magnetocaloric effect has been estimated in terms of both isothermal magnetic entropy and adiabatic temperature changes. The highest adiabatic temperature change ΔT{sub ad}=3 K and highest isothermal entropy change ΔS{sub mag}=12.1 J/kg K were observed for (Ho{sub 0.9}Er{sub 0.1}){sub 0.95}Gd{sub 0.05}Co{sub 2} at ∼90 K in magnetic fields of 2 T and 3 T, respectively. A decrease in the entropy change has been observed with increasing Gd content in all studied samples. The smallest values of ΔS{sub mag} were observed for the (Dy{sub 0.9}Ho{sub 0.1}){sub 1−x}Gd{sub x}Co{sub 2} solid solutions. Under an external field change of from 0 to 3 T, the maximum entropy change for (Dy{sub 0.9}Ho{sub 0.1}){sub 1−x}Gd{sub x}Co{sub 2} compounds decreases from 6.9 at x=0.05–4.3 J/kg K at x=0.15. The refrigerant capacity for all solid solutions (with 0.05≤x≤0.15) is reported. The effect of increasing Gd content in the solid solutions on their magnetic and magnetocaloric properties is discussed. - Graphical abstract: Temperature dependencies of ΔT{sub ad} induced by µ{sub 0}H=1 and 2 T in (a) (Ho{sub 0.9}Er{sub 0.1}){sub 1−x}Gd{sub x}Co{sub 2} and (b) (Dy{sub 0.9}Er{sub 0.1}){sub 1−x}Gd{sub x}Co{sub 2} solid solutions. Display Omitted.

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

Sol–gel method as a way of carbonyl iron powder surface modification for interaction improvement

This article presents a method for modification of carbonyl iron particles’ surface (CIP), (d{sub 50}=4–9 µm) by silica coatings obtained using the sol–gel method. Reaction parameters were determined to obtain dry magnetic powder with homogeneous silica coatings without further processing and without any by-product in the solid or liquid phase. This approach is new among the commonly used methods of silica coating of iron particles. No attempt has been made to cover a carbonyl iron surface by silica in a waste-free method, up to date. In the current work two different silica core/shell structures were made by the sol–gel process, based on different silica precursors: tetraethoxy-silane (TEOS) and tetramethoxy-silane (TMOS). The dependence between the synthesis procedure and thickness of silica shell covering carbonyl iron particles has been described. Surface morphology of the modified magnetic particles and the coating thickness were characterized with the use of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Determination of the physicochemical structure of the obtained materials was performed by the energy-dispersive X-ray spectroscope (EDS), and the infrared technique (IR). The surface composition was analyzed using X-ray photoelectron spectroscopy (XPS). Additionally, distribution of particle size was measured using light microscopy. The new, efficient process of covering micro-size CIP with a nanometric silica layer was shown. Results of a performed analysis confirm the effectiveness of the presented method. - Highlights: • Proper covering CIP by sol–gel silica layer avoids agglomeration. • A new solid waste-free method of CIP coating is proposed. • Examination of the properties of modified CIP in depends on washing process. • Coatings on CIP particles doesn’t change the magnetic properties of particles.

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

Quaternary rare-earth arsenides REAg{sub 1−x}Zn{sub y}As{sub 2} (RE=La–Nd, Sm, Gd–Dy) with tetragonal SrZnBi{sub 2}- and HfCuSi{sub 2}-type structures

Reactions of the elements at 800 °C with the nominal compositions REAg{sub 1−x}Zn{sub x}As{sub 2} resulted in quaternary arsenides REAg{sub 1−x}Zn{sub y}As{sub 2} in which the combined Ag and Zn content deviates increasingly from unity in the Zn-richer phases, reflecting the transition from the fully stoichiometric ternary silver-containing arsenides REAgAs{sub 2} to the substoichiometric zinc-containing ones REZn{sub 0.67}As{sub 2}. Powder X-ray diffraction analysis indicated SrZnBi{sub 2}-type (space group I4/mmm, Z=4; RE=La, Ce) and HfCuSi{sub 2}-type structures (space group P4/nmm, Z=2; RE=Pr, Nd, Sm, Gd, Tb, Dy). Single-crystal X-ray diffraction analysis performed on LaAg{sub 0.5}Zn{sub 0.5}As{sub 2}, PrAg{sub 0.5}Zn{sub 0.5}As{sub 2}, and NdAg{sub 0.5}Zn{sub 0.5}As{sub 2} indicated that the Ag and Zn atoms are disordered within metal-centred tetrahedra and provided no evidence for distortion of the square As nets. The small electron excess tolerated in these quaternary arsenides and the absence of distortion in the square nets can be traced to the occurrence of As–As states that are only weakly antibonding near the Fermi level. PrAg{sub 0.5}Zn{sub 0.5}As{sub 2} and NdAg{sub 0.5}Zn{sub 0.5}As{sub 2} are paramagnetic with effective magnetic moments consistent with trivalent RE species. - Graphical abstract: On proceeding from fully stoichiometric REAgAs{sub 2} to substoichiometric REZn{sub 0.67}As{sub 2}, deficiencies in Zn content become increasingly prominent in quaternary arsenides REAg{sub 1−x}Zn{sub y}As{sub 2}. - Highlights: • Ag and Zn atoms are disordered within quaternary arsenides REAg{sub 1−x}Zn{sub y}As{sub 2}. • In Zn-richer phases, Zn deficiencies develop to counteract electron excess. • Distortions of square As net appear to be suppressed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗