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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

MnRhBi 3 : A Cleavable Antiferromagnetic Metal

Cleavable metallic antiferromagnets may be of use for low-dissipation spintronic devices; however, few are currently known. Here, in this study, we present orthorhombic MnRhBi 3 as one such compound and present a thorough study of its physical properties. Exfoliation is demonstrated experimentally, and the cleavage energy and electronic structure are examined by density functional theory calculations. It is concluded that MnRhBi 3 is a van der Waals-layered material that cleaves easily between neighboring Bi layers and that the Bi atoms have lone pairs extending into the van der Waals gaps. A series of four phase transitions are observed below room temperature, and neutron diffraction shows that at least two of the transitions involve the formation of antiferromagnetic order. Anomalous thermal expansion points to a crystallographic phase transition and/or strong magnetoelastic coupling. This work reveals a complex phase evolution in MnRhBi 3 and establishes this cleavable antiferromagnetic metal as an interesting material for studying the interplay of structure, magnetism, and transport in the bulk and ultrathin limits, as well as the role of lone pair electrons in interface chemistry and proximity effects in van der Waals heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2026

MnRhBi3: A Cleavable Antiferromagnetic Metal

This dataset contains DFT input and output files supporting the theoretical modeling in the associated publication (Chem. Mater. 2024, 36, 11306-11316). The calculations characterize MnRhBi3, an orthorhombic (Cmmm) van der Waals-layered intermetallic compound that cleaves easily between neighboring Bi layers. The dataset is organized into three calculation types: (i) Bulk: Structural relaxations of the periodic MnRhBi3 crystal in antiferromagnetic (AFM) and ferromagnetic (FM) configurations, using the vdW-DF-optB86b functional. These provide the equilibrium lattice constants, magnetic energy differences (AFM is 0.5 meV/f.u. lower than FM), and magnetic moments (4.4 µB/Mn, 0.17 µB/Rh, 0.18 µB/Bi) reported in Table 1 of the main text. (ii) Slab: Same magnetic configurations computed with an 18 Ang vacuum layer introduced between Bi layers, used to calculate the cleavage energy Ec = 0.56 J/m2 (AFM) and 0.57 J/m2 (FM), establishing MnRhBi3 as a van der Waals-layered material comparable to graphite, MoS2, and CrI3. (iii) ELF: Single-point calculation on the relaxed bulk AFM geometry with LELF=.TRUE., producing the ELFCAR file used to generate electron localization function isosurfaces and contour maps (Fig. 2, main text) showing Bi lone pairs directed into the van der Waals gaps. All folders contain CONTCAR, INCAR, KPOINTS, OUTCAR, and POSCAR. The ELF/ folder additionally contains ELFCAR. Calculations were performed using VASP 6.3.2 with PBE + vdW-DF-optB86b, PAW potentials, and an energy cutoff of 800 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Deep operator network surrogate for phase-field modeling of metal grain growth during solidification

A deep operator network (DeepONet) has been constructed that generates accurate representations of phase-field model simulations for evolving two dimensional metal grain morphology growing from melt. These representations serve as lower resolution, computationally efficient stand-ins for quick parameter space exploration of solutions to the the Allen-Cahn equations that dictate the phase-field model simulations. The experimental target for the phase-field model is a uranium casting system cooling a 434 g uranium charge from a maximum temperature of 1400° C at an average rate of 30° C / min , traversing the crystallographic phases of the pure metal. Experimental parameters inform the phase-field model, whose higher resolution computational model solutions are used to train the DeepONet in a given parameter space with the aim of developing a faster, more efficient method for predicting the solidifying metal's microstructure at different potential experimental values. The final DeepONet generates high accuracy, lower resolution predictions with cumulative relative approximation error over all timesteps of less than 0.5%, while ensuring solutions remain within physically feasible ranges. Further, these relative error values are comparable with other state-of-the-art DeepONet models for microstructure evolution, while significantly reducing the amount of training data required. Training a convolutional neural network simultaneously with the DeepONet, enforcing realistic values at the complex metal grain boundaries, and mathematically encoding boundary conditions into the structure of the DeepONet improved prediction accuracy and computational efficiency over a standard DeepONet model.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Enhanced ferroelectric and piezoelectric properties of BCT-BZT at the morphotropic phase boundary driven by the coexistence of phases with different symmetries

The discovery of lead-free piezoelectric materials is crucial for future information and energy storage applications. Enhanced piezoelectric and other physical properties are commonly observed near the morphotropic phase boundary (MPB) composition of ferroelectric solid solutions. The (1 – x)Ba(Zr 0.2 Ti 0.8 )O 3 -x(Ba0.7Ca0.3)TiO 3 (BZT-xBCT) system exhibits a large electromechanical response around its MPB region at x = 0.5. Here, we report experimental and theoretical results of BZT-xBCT over a wide composition range (0.3 ≤ x ≤ 1.0). X-ray diffraction and Raman spectroscopy studies indicate a composition-induced structural phase transition from a rhombohedral (R3m) phase at x ≤ 0.4 to a tetragonal (P4mm) phase at x ≥ 0.6 through a multiphase coexistence region at 0.45 ≤ x ≤ 0.55 involving orthorhombic + tetragonal (Amm2 + P4mm) phases. First-principles calculations elucidate the phase competition in the coexistence region. The critical composition (x = 0.5) displays enhanced dielectric, ferroelectric, and piezoelectric properties, where notably d 33 ~ 320 pC/N. This paper provides clear evidence of Amm2+P4mm crystallographic phases in the MPB region, which is responsible for the improved functional properties.

MPB↗
DOE OSTI2025

Dimensional Control in Phase-Pure Coevaporated Quasi-2D Ruddlesden–Popper Structures

Fast, uncontrolled crystallization with several competing pathways makes solution-processing of phase-pure quasi-two-dimensional (quasi-2D) metal halide Ruddlesden–Popper thin films challenging. Typically, solution-processing results in the formation of different structural phases with varying dimensionality ranging from 2D, to quasi-2D, and 3D, introducing bandgap disorder and inhibiting charge transport. In this work, we eliminate interactions between precursor salts and solvents by using controlled thermal coevaporation to grow quasi-2D thin films that show high phase purity and narrow phase distribution. We study the structural landscape using synchrotron-based X-ray scattering and charge-carrier dynamics using ultrafast pump–probe spectroscopy. We then demonstrate a strategy to control the crystallographic phase of the film through phosphonic acid-based surface modification. We use density functional theory to study the interactions between propylphosphonic acid and the organic precursors and find that the interactions of loosely bound phosphonic acid molecules with evaporated precursors, followed by the migration of phosphonic acids through the deposited thin film, dictate the film structure between 2D and quasi-2D phases. These findings introduce new solvent-free methods for the fabrication of phase-pure quasi-2D Ruddlesden–Popper thin films and control phase selectivity across different dimensional (2D and quasi-2D) structures.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ion irradiation induced phase transformation in gold nanocrystalline films

Gold is a noble metal typically stable as a solid in a face-centered cubic (FCC) structure under ambient conditions; however, under particular circumstances aberrant allotropes have been synthesized. In this work, we document the phase transformation of 25 nm thick nanocrystalline (NC) free-standing gold thin-film via in situ ion irradiation studied using atomic-resolution transmission electron microscopy (TEM). Utilizing precession electron diffraction (PED) techniques, crystallographic orientation and the radiation-induced relative strains were measured and furthermore used to determine that a combination of surface and radiation-induced strains lead to an FCC to hexagonal close packed (HCP) crystallographic phase transformation upon a 10 dpa radiation dose of Au 4+ ions. Contrary to previous studies, HCP phase in nanostructures of gold was stabilized and did not transform back to FCC due to a combination of size effects and defects imparted by damage cascades.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Selective Catalytic Behavior Induced by Crystal–Phase Transformation in Well–Defined Bimetallic Pt–Sn Nanocrystals

The Pt-Sn bimetallic system is a much studied and commercially used catalyst for propane dehydrogenation. The traditionally prepared catalyst, however, suffers from inhomogeneity and phase separation of the active Pt–Sn phase. Colloidal chemistry offers a route for the synthesis of Pt–Sn bimetallic nanoparticles (NPs) in a systematic, well-defined, tailored fashion over conventional methods. Here, the successful synthesis of well-defined ≈2 nm Pt, PtSn, and Pt 3 Sn nanocrystals with distinct crystallographic phases is reported; hexagonal close packing (hcp) PtSn and fcc Pt 3 Sn show different activity and stability depending on the hydrogen-rich or poor environment in the feed. Moreover, face centred cubic (fcc) Pt 3 Sn/Al 2 O 3 , which exhibited the highest stability compared to hcp PtSn, shows a unique phase transformation from an fcc phase to an L1 2 -ordered superlattice. Contrary to PtSn, H 2 cofeeding has no effect on the Pt 3 Sn deactivation rate. Finally, the results reveal structural dependency of the probe reaction, propane dehydrogenation, and provide a fundamental understanding of the structure–performance relationship on emerging bimetallic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Structural modulation and spin glassiness upon oxidation in oxygen storage material LnFeMnO 4+x for Ln = Y, Lu, and Yb

The mixed valence multiferroic LnFe 2+ Fe 3+ O 4 (where Ln = Y, Lu, and Yb) can reversibly uptake oxygen into its lattice, which is evidenced by a crystallographic phase transition along with the appearance of structural modulations. In this study, we show that the Mn-substituted version of this multiferroic can also be readily oxidized to LnFe 3+ Mn 3+ O 4.5 revealing similar oxygen storage behavior. Through neutron, electron, and synchrotron x-ray diffraction studies, we observe a structural modulation that we attribute to a displacement wave in the fully oxidized compound. This wave exhibits commensurability with a wavevector q = (-2/7, 1/7, 0). Bond valence summation analysis of plausible interstitial oxygen positions suggests that oxygen insertion likely occurs at the middle of the Fe/Mn–O bipyramid layers. The structural modulation of LnFeMnO 4.5 is two-dimensional, propagates along the ab-plane, and is highly symmetric as 12 identical modulation vectors are observed in the diffraction patterns. The nature of the lanthanide, Ln 3+ , does not seem to influence such modulations since we observe identical satellite reflections for all three samples of Ln = Y, Lu, and Yb. Both LnFeMnO 4 and LnFeMnO 4.5 display spin glassy behavior with 2D short-range magnetic ordering being observed in LnFeMnO 4 . Analysis of the neutron diffraction data reveals a correlation length of ~10 nm. Upon oxidation to LnFeMnO 4.5 , the short-range magnetic order is significantly suppressed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of Local Structural Distortions on Antiferroelectric–Ferroelectric Phase Transition in Dilute Solid Solutions of K x Na 1– x NbO 3

The fundamental principles that govern antiferroelectric (AFE)–ferroelectric (FE) transitions are not well understood for many solid solutions of perovskite compounds. For example, crystal chemical considerations based on the average Goldschmidt tolerance factor or ionic polarizability do not precisely predict the boundary between the AFE and FE phases in dilute solid solutions of alkali niobates, such as K x Na 1– x NbO 3 ( x ≤ 0.02). Here, based on detailed structural analysis from neutron total scattering experiments, we provide insights about how the relative local distortions around the A- and B-sites of the ABO 3 perovskite structure affect the AFE/FE order of the average crystallographic phases in K x Na 1– x NbO 3 . Specifically, we show that a higher (lower) ratio of B-site-centered distortions over A-site-centered distortions drives transition toward a long-range FE (AFE) phase, which is based on a competition between the long-range polarizing field of the Nb–O dipoles and the disordering effect of local distortions around the A-site. Our study provides a predictive tool for designing complex solid-solution perovskites with tunable (anti)ferroelectric polarization properties, which can be of interest for various energy-related applications such as high-density energy storage and solid-state cooling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Plutonium migration and phase evolution in irradiated U-Pu-Zr metallic fuels: An integrated EPMA-SEM-TEM study

Constituent redistribution is a defining feature of irradiated U-Pu-Zr metallic fuels, yet its mechanisms and effects on fuel performance are not sufficiently resolved to guide model development. Although decades of irradiation testing have established broad trends, a true mechanistic understanding of constituent redistribution has not been achieved. Here, in this study, we use electron probe microanalysis (EPMA), scanning electron microscopy (SEM), and transmission electron microscopy-based (TEM) selective area electron diffraction (SAED) on a EBR-II irradiated U-19 wt.% Pu-6 wt.% Zr fuel pin cross-section to correlate the composition, porosity, and crystallographic phases formed after irradiation. Constituent redistribution is thought to consist of three distinct zones, in which uranium and zirconium migrate while plutonium remains relatively unchanged. Our EPMA results resolve eight distinct compositional regions, and more importantly, show that plutonium redistributes alongside zirconium, contrary to historical assumptions. The distribution of fission products was highly asymmetric with a few large lanthanide precipitates observed at isolated sites on the pin periphery instead of a uniform distribution of smaller precipitates around the periphery. Using thermodynamic data from TAF-ID and the measured EPMA compositions, matrix phase fractions were predicted across the fuel radius. Phase predictions based on composition did not match TEM/SAED results, which revealed a much higher fraction of α−U phase than would be expected if phases were retained from reactor temperatures. These findings highlight the need for expanded SAED phase identification to capture post-irradiation and storage effects, as well as rigorous uncertainty quantification in fuel performance and phase diagram modeling to better constrain predictions from compositional data.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS2003

Scandia-and-Yttria-Stabilized Zirconia for Thermal Barriers

yttria in suitable proportions has shown promise of being a superior thermal- barrier coating (TBC) material, relative to zirconia stabilized with yttria only. More specifically, a range of compositions in the zirconia/scandia/yttria material system has been found to afford increased resistance to deleterious phase transformations at temperatures high enough to cause deterioration of yttria-stabilized zirconia. Yttria-stabilized zirconia TBCs have been applied to metallic substrates in gas turbine and jet engines to protect the substrates against high operating temperatures. These coatings have porous and microcracked structures, which can accommodate strains induced by thermal-expansion mismatch and thermal shock. The longevity of such a coating depends upon yttria as a stabilizing additive that helps to maintain the zirconia in an yttria-rich, socalled non-transformable tetragonal crystallographic phase, thus preventing transformation to the monoclinic phase with an associated deleterious volume change. However, at a temperature greater than about 1,200 C, there is sufficient atomic mobility that the equilibrium, transformable zirconia phase is formed. Upon subsequent cooling, this phase transforms to the monoclinic phase, with an associated volume change that adversely affects the integrity of the coating. Recently, scandia was identified as a stabilizer that could be used instead of, or in addition to, yttria. Of particular interest are scandia-and-yttria-stabilized zirconia (SYSZ) compositions of about 6 mole percent scandia and 1 mole percent yttria, which have been found to exhibit remarkable phase stability at a temperature of 1,400 C in simple aging tests. Unfortunately, scandia is expensive, so that the problem becomes one of determining whether there are compositions with smaller proportions of scandia that afford the required high-temperature stability. In an attempt to solve this problem, experiments were performed on specimens made with reduced proportions of scandia. The criterion used to judge these specimens was whether they retained the non-transformable tetragonal phase after a severe heat treatment of 140 hours at 1,400 C.

Mess, Derek↗
DOE OSTI2020

Potential Control of Oxygen Non-Stoichiometry in Cerium Oxide and Phase Transition Away from Equilibrium

Cerium oxide (ceria, CeO 2 ) is a technologically important material for energy conversion applications. Its activities strongly depend on redox states and oxygen vacancy concentration. Understanding the functionality of chemical active species and behavior of oxygen vacancy during operation, especially in high-temperature solid-state electrochemical cells, is the key to advance future material design. Herein, the structure evolution of ceria is spatially resolved using bulk-sensitive operando X-ray diffraction and spectroscopy techniques. During water electrolysis, ceria undergoes reduction, and its oxygen non-stoichiometry shows a dependence on the electrochemical current. Cerium local bonding environments vary concurrently to accommodate oxygen vacancy formation, resulting in changes in Ce-O coordination number and Ce 3+ /Ce 4+ redox couple. When reduced enough, a crystallographic phase transition occurs from α to an α' phase with more oxygen vacancies. Nevertheless, the transition behavior is intriguingly different from the one predicted in the standard phase diagram of ceria. This work demonstrates a feasible means to control oxygen non-stoichiometry in ceria via electrochemical potential. It also sheds light on the mechanism of phase transitions induced by electrochemical potential. For electrochemical systems, effects from a large-scale electrical environment should be taken into consideration, besides effective oxygen partial pressure and temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Highly Efficient Uniaxial In-Plane Stretching of a 2D Material via Ion Insertion

On-chip dynamic strain engineering requires efficient micro-actuators that can generate large in-plane strains. Inorganic electrochemical actuators are unique in that they are driven by low voltages (≈1 V) and produce considerable strains (≈1%). However, actuation speed and efficiency are limited by mass transport of ions. Minimizing the number of ions required to actuate is thus key to enabling useful “straintronic” devices. Here, it is shown that the electrochemical intercalation of exceptionally few lithium ions into WTe 2 causes large anisotropic in-plane strain: 5% in one in-plane direction and 0.1% in the other. This efficient stretching of the 2D WTe 2 layers contrasts to intercalation-induced strains in related materials which are predominantly in the out-of-plane direction. The unusual actuation of Li x WTe 2 is linked to the formation of a newly discovered crystallographic phase, referred to as Td', with an exotic atomic arrangement. On-chip low-voltage (<0.2 V) control is demonstrated over the transition to the novel phase and its composition. Within the Td'-Li 0.5-δ WTe 2 phase, a uniaxial in-plane strain of 1.4% is achieved with a change of δ of only 0.075. This makes the in-plane chemical expansion coefficient of Td'-Li 0.5-δ WTe 2 far greater than of any other single-phase material, enabling fast and efficient planar electrochemical actuation.

36 MATERIALS SCIENCE↗
DOE OSTI2026

A comparative study on cubic and tetragonal Ce-ZrO 2 supported Rh catalysts for N 2 O decomposition

Zirconium oxide (ZrO 2 ) exhibits strong synergy with cerium oxide (CeO 2 ), acting as a structural and electronic promoter during catalytic redox reactions. As a result, Ce-ZrO 2 composite oxides are widely used as supports in various catalytic systems. In our previous work, we demonstrated that the incorporation of Zr 4+ into the CeO 2 lattice significantly enhanced Rh dispersion, improved redox ability, and stabilized surface Rh species, which collectively boosted the de-N 2 O activity of Rh/Ce-ZrO 2 catalysts. Building on these findings, the present study emphasizes that the crystallographic phase of Ce-ZrO 2 , governed by the Ce/Zr ratio, plays a decisive role in tuning the physicochemical environment of Rh active sites and thereby optimizing catalytic performance. In conclusion, tailoring the Ce/Zr ratio to favor the cubic fluorite structure emerges as a promising strategy for the rational design of highly active and stable catalysts for N 2 O decomposition and potentially other redox-sensitive environmental applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Proton irradiation effects in Molybdenum-Carbide-Graphite composites

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) has prompted the investigation of novel materials for beam-intercepting devices, and in particular for the collimators responsible for protecting the machine from beam losses. The HL-LHC collimation system will inevitably experience increased levels of radiation damage and undergo changes in their crucial physio-mechanical properties. Graphite-matrix composite materials containing molybdenum carbide particles, along with small amounts of titanium carbide, were developed with the objective of enhanced in-beam performance and tested under proton irradiation. The physical degradation observed in early grades of molybdenum carbide compounds, even after modest proton fluences, has prompted the development of advanced compounds. In this work, we examine the effects of proton irradiation on the microstructural and thermophysical properties of new grades of Molybdenum-carbide-graphite compounds up to fluences of ~2 × 10 20 p/cm 2 . Here, we employ a combination of precision dilatometry and high-energy X-ray diffraction to quantify the dimensional stability and crystallographic phase evolution both pre- and post-irradiation. Our results reveal that these new compounds exhibit superior resilience to radiation damage than their predecessors.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Extreme fast charge aging: Correlation between electrode scale and heterogeneous degradation in Ni-rich layered cathodes

Extreme fast charging (XFC) is a key requirement for the adoption of battery-based electric vehicles by the transportation sector. However, XFC has been shown to accelerate degradation, causing the capacity, life, and safety of batteries to deteriorate. There are no systematic studies in the open literature regarding aging modes in Ni-rich Li y Ni 0.a Mn 0.b Co 0.c O 2 (NMCabc) cathodes caused by fast charging. Herein, we report the effects of cathode composition and electrode loading in pouch cells containing NMC532, 622 and 811 paired with graphite and cycled under XFC conditions. The relative anisotropic volume change in the unit cell increases with Ni content in low-loading cells, while it levels up for all three NMC cathodes in high-loading cells because of substantial Li plating. The amounts of lithium plating and heterogeneity on the anode, determined by crystallographic phase quantification, were found to be correlated with electrode loading and cathode heterogeneity. The concentrations of the transition metals deposited on the anodes depend on NMCabc composition in a complex way. More particle cracking and surface degradation was found in NMC811. Here, the findings in this work provide a new understanding of the failure mechanisms and their practical implications for compositional tuning of future high-Ni NMCabc cathode materials during fast charging.

25 ENERGY STORAGE↗
DOE OSTI2024

Unraveling the multi-step crystallization mechanism of polytetrafluoroethylene, modified polytetrafluoroethylene, and their nanocomposites with boron nitride nanobarbs: Experimental insights and theoretical analysis

The non-isothermal crystallization behavior and kinetics of polytetrafluoroethylene (PTFE) composites with boron nitride nanobarb (BNNB), a new generation nanostructure with unique surface morphology and mechanical “barbs” have been analyzed, understanding these properties is essential for their high-end applications as thermal interface materials (TIM) for microwave, 5G and microelectronic devices. The analysis of the crystallization parameters includes crystallization onset, peak and end temperatures, crystallization half-life and overall crystallinity of PTFE, modified PTFE and their BNNB composites. The results were further analyzed using theoretical models such as the combined Avrami-Ozawa model. It was found that BNNB supports crystallization in the modified PTFE but shows minimal effect on the crystallization of PTFE. Due to the limitation of the classical theoretical models used above in fully characterizing the multi-step crystallization process of PTFE, an in-depth analysis using the model-free advanced isoconversional computation was used to characterize the PTFE crystallization based on the evolution of activation energy with fractional crystallinity and for the first time with temperature. Three kinetic regions were identified in the crystallization mechanism. Here, this study investigated the molecular organization and microstructural evolution of PTFE, modified PTFE and their composites during non-isothermal crystallization using advanced X-ray scattering measurements. An insight into the changes undergone by the material's microstructural units including crystallite size and morphology, lamellar thickness and lamellar interfacial layer thickness, and crystallographic phase dynamics during non-isothermal cooling from the melt, was provided here in this work. The effect of copolymer modification of PTFE and the inclusion of pristine and functionalized BNNB (a thermally conductive and electrically insulating ceramic) are both new investigations that provide valuable knowledge for the development of materials with strong matrix-nanofiller interaction and guidance for optimizing sintering and cooling cycles, two key steps in PTFE processing that largely affect the material microstructural features. Overall, the result of the three-part investigation demonstrates that BNNB supports crystallization in the modified PTFE up to 20 wt% concentration and at low and high cooling rates typically used in the industrial processing of PTFE.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effects of growth rate and dynamic substrate tilt on properties of Au-Ta alloy films deposited by high-power impulse magnetron sputtering

Gold-tantalum (Au—Ta) alloys are promising for next-generation hohlraums for magnetically-assisted indirect-drive inertial confinement fusion. Hohlraum fabrication involves sputter deposition of ultrathick coatings on sphero-cylindrical substrates. The control of physical properties of such coatings remains a challenge. Here, in this work, we systematically study effects of the growth rate and dynamic substrate tilt on properties of AuTa 4 films deposited onto rotating planar substrates mounted at different tilt angles to mimic different regions of the sphero-cylindrical surface of a hohlraum. We use high-power impulse magnetron sputtering (HiPIMS) in the constant charge per pulse mode with a pulse duration of 100 μs, a charge per pulse of 190 μC, a peak target current of about 3 A, and the pulse frequency varied in the range of 400–1400 Hz. The Langmuir probe, mass-resolved ion energy spectrometry, and optical emission spectroscopy are used to monitor plasma discharge characteristics in order to isolate and study effects of the growth rate. The deposition rate and the ballistics and energetics of depositing species are estimated by Monte Carlo simulations. Results show that the film microstructure, crystallographic phase, residual stress, and electrical resistivity strongly depend on both the deposition rate and substrate tilt, highlighting their critical role in tailoring properties of Au—Ta films during hohlraum fabrication.

36 MATERIALS SCIENCE↗