ICMCTF 2026 Session MA3-1-TuM: High Entropy and Other Multi-principal-element Materials I

In indirect-drive inertial confinement fusion (ICF) experiments at the National Ignition Facility (NIF), the hohlraum plays a critical role in achieving increased implosion yield, as it drives the fuel capsule’s compression. Our simulations with the radiation hydrodynamics code LASNEX suggest that the fusion yield can be improved by using hohlraums made of high entropy alloys (HEAs) containing rare-earth (RE) elements. Here, we present results from a systematic study using combinatorial radio-frequency magnetron co-sputtering to develop a family of Gd-Ta-W-Au-Bi coatings with properties favorable for ICF applications, including high electrical resistivity for consideration in magnetically-assisted ICF schemes. These results provide a framework for the future development of RE-HEA hohlraum materials.

This work was performed under the auspices of the U.S. DOE by LLNL under Contract AC52-07NA27344 and was supported by the LLNL-LDRD Program under Project No. 26-ERD-011.

A hohlraum, centimeter-scale sphero-cylindrical heavy-metal cans with wall thicknesses of 10–100 µm, is a key component of indirect-drive inertial confinement fusion (ICF) targets, as they determine the x-ray drive that implodes the fuel capsule. Our simulations predict that hohlraums made from rare-earth-containing high-entropy alloys (RE-HEAs) or depleted-uranium-containing high-entropy alloys (DU-HEAs) can achieve significantly higher x-ray coupling efficiencies than the best-performing single-element hohlraums made from Au or DU. Here, we present our progress in developing sputter-deposited RE- and DU-HEAs with material properties compatible with ICF target fabrication processes.

This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344 and LDRD project 26-ERD-011.

Materials and Data sciences convergence is the new paradigm governing the discovery acceleration of new materials, always more complex and integrating, in a virtuous approach, new durability and sovereignty requirements. Every great transitions are concerned : towards a sustainable future and energies, towards frugal digital applications, towards a medicine of the future always more customized/personalised. In France, this dynamic is organised at the national level by the PEPR DIADEM, a program gathering universities and research institutes to shape and promote this trend.

In this race to the discovery acceleration of materials, artificial intelligence may play a significant role in always more complex synthesis and shaping processes proficiency. Among these high impact generic processes for many industrial sectors, thin film deposition technologies play a key role, in particular driven towards excellence by constraints and specifications imposed by the requirements always more specific of microelectronics applications.

Consequently, highly ionized PVD processes like HiPIMS emerged in this dynamic and now are being developed in many other domains like sustainable energies, in particular in nuclear applications, and also for green hydrogen via electrolysis, photovoltaics and marine energy.

We will present two developments using a hybrid pulsed-DC/HiPIMS multi cathode system :

• a new refractory HEA diffusion barrier layer for nuclear claddings on one hand : To prevent loss of coolant accident, fuel claddings in zirconium alloys are now coated with PVD chromium, but at 1320°C an eutectic phase may occur. Hence, we are developing a refractory V-Nb-Mo-W diffusion barrier to avoid the formation of this eutectic phase (ASTERIX project of PEPR DIADEM).
• new HEA coatings for corrosion in molten salt dedicated to Small Modular Reactors, on the other hand : we will explore the feasibility of Ni-Al-Cr-Mo alloys (A-DREAM project of PEPR DIADEM).

Combinatorial approaches made possible by instrumented multi-target PVD technologies, coupled to artificial intelligence allowing the extraction of inter-parametric relations between processes parameters, are at the heart of this study dedicated to the development of a hybrid pulsed-DC/HiPIMS PVD process digital twin for the deployment of complex coatings for extreme media.

Refractory high entropy TiTaZrHfW-N/Si₃-N₄ nano-layered alloy thin films are investigated to study the effect of nano-layered architecture and silicon (Si) mean content on their structural, mechanical, thermal properties and oxidation behavior. The films are deposited using direct current (DC) magnetron sputtering of separate Si and TiTaZrHfW targets. The Si mean content is controlled by tailoring the power discharge applied to the Si target. The deposition process led to a nano-layered architecture where Si₃N₄ (amorphous) and TiTaZrHfW-N (nano-crystalized NaCl FCC type structure) are alternated. By increasing the thickness of Si₃N₄ nano-layers, the Si mean content increases. All coatings are found to have good thermal stability after annealing under vacuum at 900 °C. Increasing Si mean content reduces the film’s hardness; however, the annealing treatment at 900 °C improves it. A super-hardness of 41 GPa is found for the post-annealed Si-free film. Si₃N₄ nano-layers enhance the oxidation resistance at elevated temperatures of 600, 700, and 800 °C. This oxidation resistance is further enhanced by increasing the nano-layer’s period and also by increasing the density of the films.

The rational design of multi-component oxide systems provides an effective pathway to balance high capacity and structural robustness in lithium-ion battery anodes. In this study, TiO₂–SnO₂ composite solid solutions were synthesized via a controlled solid-state reaction to explore the interplay between structural evolution and electrochemical performance. Structural analyses (XRD and TEM) confirmed the partial incorporation of Sn⁴⁺ into the rutile TiO₂ lattice, accompanied by limited phase segregation into SnO₂-rich domains at higher Sn contents. The coexistence of solid-solution and segregated regions generated a nanoscale heterostructure that enhanced Li⁺ diffusion and mitigated volume fluctuation during cycling. Among the synthesized samples, ST1450 initially delivered the highest capacity of 635.5 mAh g⁻¹ at 0.2 C, but gradually declined to 231.9 mAh g⁻¹ after 100 cycles, corresponding to the lowest degree of phase segregation. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) analyses revealed that coherent TiO₂/SnO₂ interfaces effectively facilitated charge-transfer kinetics while preserving mechanical integrity. The optimized ST1450 sample exhibited an extremely low charge-transfer resistance of 3.85 Ω, reflecting improved electronic transport pathways. Furthermore, in-situ XRD measurements directly captured phase transitions during lithiation and delithiation, providing crucial insight into the dynamic reaction mechanism. The observed spinodal decomposition within the TiO₂–SnO₂ system forms a self-organized nanoscale microstructure that reinforces both ionic transport and structural stability. These results elucidate the lithiation pathway of TiO₂–SnO₂ composite oxides and highlight spinodal decomposition as a promising strategy for developing structurally adaptive, high-performance oxide anodes for next-generation lithium-ion batteries.

Keywords: Composite oxides, Anode materials, Fast-charging materials, In-situ XRD, Solid-state reaction

Hydrogen is widely recognized as a promising clean energy carrier, with the hydrogen evolution reaction (HER) serving as a crucial step in sustainable hydrogen production. Transition-metal phosphides have attracted considerable attention owing to their excellent electrical conductivity and catalytic activity. In this study, Fe–Co–Ni phosphides were synthesized via a solution-based precursor route followed by phosphorization, forming nanostructured multimetallic phases with uniform morphology. Transmission electron microscopy (TEM) revealed nanoscale features, while energy-dispersive X-ray spectroscopy (EDS) confirmed the homogeneous distribution of Fe, Co, and Ni.

Electron energy loss spectroscopy (EELS) played a central role in elucidating the electronic structure evolution of the catalysts. The spectra revealed distinct edges corresponding to O (538.5 eV), Fe (712.0 eV), Co (783.0 eV), and Ni (857.0 eV), clearly reflecting the hybridization between metal 3d and P 2p orbitals and providing direct evidence of charge redistribution among the transition-metal sites. These findings demonstrate the strong correlation between the local electronic configuration and catalytic performance.

Electrochemical analysis further confirmed that Fe–Co–Ni phosphides exhibit remarkable HER activity, requiring only -0.176 V overpotential to reach −10 mA cm⁻². The polarization (I–V) curves showed rapid current response and low activation energy, while a Tafel slope of 109 mV dec⁻¹ indicated a favorable Volmer–Heyrovsky mechanism. Long-term chronoamperometric measurements verified excellent durability, and subsequent durability and accelerated cycling tests lasting up to 100 hours will be conducted to comprehensively evaluate structural and electrochemical stability under realistic conditions.

This work not only demonstrates the successful synthesis of multimetallic phosphides but also highlights EELS as a powerful tool for probing the structure–property relationship, offering valuable insights for the rational design of efficient and durable hydrogen electrocatalysts.

Nanostructured thin films continue to draw considerable attention owing to their unique and tunable properties, governed by composition, structure, and morphology. Precise control of synthesis parameters enables tailoring of film architecture and optimization of functional performance. Previous studies have shown that binary metal/carbon (Me/C) nanocomposites (Me = Ni, Co) can form amorphous, self-organized films via magnetron sputtering, characterized by high-aspect-ratio nanocolumns that may induce anisotropic behavior. These findings have inspired the development of multicomponent coatings with precisely engineered compositions and structures to further enhance performance in targeted applications.

An investigated approach employed NiMo-C coatings, synthesized with reactive magnetron sputtering of a Ni₈₀Mo₂₀ alloy in an acetylene atmosphere, as catalysts for the hydrogen evolution reaction (HER) in an acidic medium. The structural, chemical, and phase evolution of the coatings with increasing carbon content (5-75 at.%) was examined using X-ray diffraction, X-ray photoelectron spectroscopy, and transmission/scanning electron microscopy. Electrical conductivity measurements, performed with a conductive atomic force microscope, complemented the structural and compositional studies. It was found that progressive carbon incorporation (20-75 at.%) induced a transition from nanocrystalline to amorphous and ultimately to a quasi-amorphous nanocolumnar architecture composed of metallic columns perpendicular to the surface and encapsulated by an amorphous carbon shell. This morphology is expected to enhance charge transport along the columnar pathways. Moreover, the coatings surface exhibited nickel-enriched conductive regions (approx. 20 nm in diameter) that act as active catalytic centers for HER, while the surrounding carbon matrix improves corrosion resistance and interfacial stability.

The pronounced chemical stability of self-organized, carbon-enriched coatings validates their suitability for both catalytic and biomedical applications. This has been demonstrated in our studies of FeNiMo-C and CoCrMo-C systems derived from the medical alloys 316L and F-1537-08. Cyclic potentiodynamic testing in simulated body fluid showed that both coating systems were highly resistant to localized corrosion, including pitting. Tribocorrosion tests on CoCrMo-C further indicated that increasing the carbon content reduced the friction coefficient to approx. 0.1. The coatings containing 40 at.% carbon exhibited the most favorable tribological performance, demonstrating the lowest friction coefficient and a low wear rate irrespective of the measurement conditions.