Open Access

Show Abstract ▼

Abstract: Ocean-bearing icy worlds may harbour the necessary conditions for life, but we do not yet understand the processes that deliver ocean fluids to the surface where they are accessible to spacecraft. We demonstrate that hydrates of sodium-chloride (NaCl), a constituent of icy world oceans, record the thermal conditions experienced by NaCl rich fluids as they freeze. Through laboratory experiments, we identify four distinct NaCl-H2O assemblages, comprising crystalline and amorphous phases. The specific phase assemblage produced by freezing of brine depends on both the cooling rate and the initial brine salinity, with the production of metastable phases favoured at lower salinities and faster cooling rates. Different NaCl–H₂O assemblages exhibit characteristic near-infrared signatures that may provide a valuable tool for interpreting data collected by upcoming orbital missions to icy worlds. These results establish that the NaCl-H2O solid phase composition could be used as a new diagnostic probe of cryogenic processes on icy worlds, providing a means to reconstruct geological history of ocean-derived surface material and enabling space missions to assess the evolution of icy worlds across the outer Solar System.

Open Access

Show Abstract ▼

Abstract: Structural degradation in Li-rich manganese-based cathodes, driven by irreversible lattice-oxygen loss and transition-metal migration, remains a key obstacle to their practical deployment in high-energy lithium-ion batteries. Here, we report a facile oxidant-driven strategy to reconstruct LiMn6 superstructure units in the Li2MnO3-like domains of Co-free Li1.2Ni0.2Mn0.6O2. Controlled re-sintering with KMnO4 treatment oxidizes a fraction of Ni2+ to Ni3+, which has a similar ionic radius to Mn4+, partially converting LiMn6 superstructure units into LiNiMn5 units. Guided by Pauling's electrostatic valence principle, the LiNiMn5-containing motifs obtained through this Ni/Mn exchange mitigate the aggregation of LiMn6 units within the Li2MnO3-like domains. Concurrently, the treatment induces surface-enriched oxygen vacancies. This synergistic effect of bulk superstructure dispersion and surface oxygen-vacancy regulation enhances oxygen redox reversibility during cycling by suppressing O–O dimerization, transition metal migration, and irreversible molecular O2 release, thereby strengthening the layered framework's stability. As a result, the modified cathode (K-LRM) delivers 231 mAh g−1 at 0.1 C and retains 83.8% of its capacity after 500 cycles at 1 C, with a reduced average voltage decay of 0.88 mV cycle−1 compared with 1.18 mV cycle−1 for the pristine LRM. This work demonstrates a simple and scalable route to tailor superstructure and anionic redox chemistry in Co-free LRM cathodes, offering general guidelines for designing next-generation high-capacity and structurally stable layered oxides.

Open Access

Show Abstract ▼

Abstract: Crystal structure prediction (CSP) from powder diffraction data is a central challenge in materials chemistry. Machine learning (ML) models show promise, but most are trained on idealized simulated data, limiting reliability on real experiments. Here, we assess real-world behaviour using the previously published deCIFer model as an example of PXRD-conditioned generative CSP. deCIFer is an autoregressive transformer that conditions each step of structure generation on encoded PXRD data, guiding token-wise predictions of space group, lattice parameters, and atomic positions. Using controlled robustness tests, we quantify performance under realistic artefacts (noise, background, peak asymmetry, and Scherrer broadening) and introduce metrics for accuracy and predictive uncertainty. deCIFer adapts smoothly to signal distortions and improves over unconditioned baselines when diffraction features remain informative, while expressing appropriate uncertainty as the PXRD pattern becomes underdetermined. Experimental PXRD tests recover the known structures of Si and CeO2 and expose the expected limitations for lower-symmetry Fe2O3 and nanocrystalline CeO2. Overall, ML-based CSP is fundamentally limited by the information content of PXRD, but can accelerate expert workflows by rapidly generating chemically plausible candidates and quantifying uncertainty, making such models valuable human-in-the-loop tools for real-world structure determination.

Show Abstract ▼

Abstract: This work revisits the K+-ion-conducting K3–xSb1–xWxS4 (0 ≤ x ≤ 0.10) system and finds a more complex structural scenario than previously reported. K3SbS4 does not only crystallize in the reported Cmc21 space group but also in a structure best described in the R3c space group. Both polymorphs are present at room temperature, whereas variable-temperature synchrotron X-ray diffraction shows that only the R3c phase persists at elevated temperatures. Similarly, the substitution of Sb(+V) with W(+VI) stabilizes the high-temperature R3c polymorph. K3SbS4 further shows similar diffusion pathways for both polymorphs. It matches the measured transport properties dominated by W(+VI) substitution, increasing ionic conductivity up to 0.64 mS·cm–1 at 298 K for nominal K2.92Sb0.92W0.08S4 with an activation energy of 0.29 eV. This work emphasizes the need for a complementary understanding of atomic arrangement and microstructure in potassium-ion conductors.

Show Abstract ▼

Abstract: The continuous increase of greenhouse gas emissions and the resulting climate change require urgent improvements in energy efficiency and decarbonization across all major industrial sectors. In the aviation and energy conversion industries, increasing operating temperatures and reducing component weight are among the most effective strategies to improve efficiency. However, the service temperatures of state-of-the-art structural materials, namely nickel-based superalloys, are already well-optimized and have reached their limit. Chromium-based alloys represent a promising alternative material class due to their high melting temperature, low density, good thermal conductivity, and favorable availability, yet their application has been historically limited by low-temperature brittleness and insufficient oxidation and nitridation resistance. This work systematically investigates Cr-based alloys, precipitation-strengthened with the Cr₃Si intermetallic phase, with the objective to extend their application window beyond that of Ni-based superalloys. The primary focus lies on the Cr-rich two-phase A2(Cr) + A15(Cr₃Si) system alloyed with molybdenum (Mo), specifically Cr-xMo-8 at.%Si alloys with Mo contents between 0 and 40 at.%. The role of Mo on phase stability, microstructure, oxidation and nitridation behavior at 1200 °C and mechanical properties from room temperature up to 1000 °C is assessed. Based on the insights gained, an alternative precipitation strategy is developed by replacing the A15((Cr,Mo)3Si) phase with low-misfit B2 (NiAl) precipitates, resulting in a BCC superalloy A2 + B2 concept within the Cr-Mo-Si-Ni-Al system. The results demonstrate that Mo is a highly effective alloying element in Cr-based alloys, providing strong solid-solution strengthening, pronounced grain refinement, suppression of nitridation, and significantly improved oxidation behavior. An optimal Mo content around 25 at.% yields an attractive combination of high specific strength (100 N·m·g⁻¹ at 1000°C vs. 40 N·m·g⁻¹ for Ni-based MAR-M-247) and oxidation resistance at temperatures up to 1200 °C, though at the expense of low fracture toughness and a higher ductile-to-brittle transition temperature. The introduction of B2 precipitates improves upon the room-temperature fracture toughness limitations of the A2 + A15 system, while enabling strength up to higher temperatures as compared to the A15- strengthened alloys. Overall, this work establishes Cr-based Cr-Mo-Si (A2 + A15) and Cr-Mo-Si-Ni-Al (A2 + B2) alloys as promising candidates for next-generation high-temperature structural materials and provides a foundation for further alloy and processing optimization.