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The development of high-performance, sustainable sodium-ion batteries requires a mechanistic understanding of cathode redox processes and structural stability. Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP) is a promising cathode material due to its non-toxicity, high average working voltage, and excellent structural and thermal stability. However, its practical application is hindered by impurity phase formation and low intrinsic electronic conductivity. To address these challenges, Na₄Fe_3-xM_x(PO₄)₂(P₂O₇) (M: Mn, Ni) composites are synthesized via a sol-gel method. A comprehensive characterization approach combining X-ray diffraction (XRD), X-ray absorption spectroscopy (XANES/EXAFS, soft XAS), and resonant inelastic X-ray scattering (RIXS) revealed that low-level substitution of Mn²⁺ and Ni²⁺ into Fe sites suppresses the formation of electrochemically inactive maricite NaFePO₄ and modifies the Fe-O coordination environment. These effects may result in lower ion migration energy barriers and better electrochemical reversibility. Among the doped samples, Mn-NFPP exhibited the best electrochemical performance, delivering a discharge capacity of ∼92 mAh g⁻¹ at 0.1 C and ∼80 mAh g⁻¹ at 2 C, with 99.5 % capacity retention after 100 cycles at 0.1 C. This work provides fundamental insights into the redox mechanism and atomic-scale structure–property relationship of NFPP, guiding the design of high-performance polyanionic cathodes for sodium-ion batteries.

We have investigated the bottom-up sol-gel synthesis of nanocomposite powders comprising two magnetic phases (hexagonal Sr ferrite and spinel Co ferrite) in order to outline a strategy to obtain permanent magnets with large coercivities via low-cost and scalable syntheses. The correlation between morphological, structural and macroscopic magnetic properties of Al-substituted SrFe₁₂O₁₉ and SrFe₁₂O₁₉/CoFe₂O₄ nanocomposites was analyzed in detail. The hysteretic behavior can be tuned by cation substitution and/or modulation of the super-exchange coupling at the interface of the constituting phases. The magnetic data, supported by Monte Carlo simulations, indicates enhanced magnetic coupling within the composite: this observation underscores the significance of soft crystallite size and epitaxial growth quality at the interface as key factors influencing super-exchange coupling strength, ranging from fully coupled to essentially decoupled composites. Bulk magnets with high density were manufactured by compacting these nanostructured phases using spark plasma sintering, without an applied magnetic field. Consolidation of powders significantly impacted magnetic properties, by increasing remanent magnetization and decreasing coercivity due to enhanced super-exchange coupling. The presence of two phases hindered reciprocal growth, influencing coercivity differently in various compositions. Overall, the compaction enhanced magnet performance through improved particle alignment and super-exchange coupling, offering the potential for optimized magnet design.

Layered TiS₂ has been proposed as a versatile host material for various battery chemistries. Nevertheless, its compatibility with aqueous electrolytes has not been thoroughly understood. Herein, we report on a reversible hydration process to account for the electrochemical activity and structural evolution of TiS₂ in a relatively dilute electrolyte for sustainable aqueous Li-ion batteries. Solvated water molecules intercalate in TiS₂ layers together with Li⁺ cations, forming a hydrated phase with a nominal formula unit of Li_0.38(H₂O)_2−δTiS₂ as the end-product. We unambiguously confirm the presence of two layers of intercalated water by complementary electrochemical cycling, operando structural characterization, and computational simulation. Such a process is fast and reversible, delivering 60 mAh g^–1 discharge capacity at a current density of 1250 mA g^–1. Our work provides further design principles for high-rate aqueous Li-ion batteries based on reversible water cointercalation.

NdGa hydride and deuteride phases were prepared from high-quality NdGa samples and their structures characterized by powder and single-crystal X-ray diffraction and neutron powder diffraction. NdGa with the orthorhombic CrBtype structure absorbs hydrogen at hydrogen pressures <= 1 bar until reaching the composition NdGaH(D)(1.1), which maintains a CrB-type structure. At elevated hydrogen pressure additional hydrogen is absorbed and the maximum composition recovered under standard temperature and pressure conditions is NdGaH(D) (1.6) with the Cmcm LaGaH1.66-type structure. This structure is a threefold superstructure with respect to the CrB-type structure. The hydrogen atoms are ordered and distributed on three fully occupied Wyckoff positions corresponding to tetrahedral (4c, 8g) and trigonal-bipyramidal (8g) voids in the parent structure. The threefold superstructure is maintained in the H-deficient phases NaGaH(D)(x) until 1.6 >= x >= 1.2. At lower H concentrations, coinciding with the composition of the hydride obtained from hydrogenation at atmospheric pressure, the unit cell of the CrB-type structure is resumed. This phase can also display H deficiency, NdGaH(D) (y) (1.1 >= y >= 0.9), with H(D) exclusively situated in partially empty tetrahedral voids. The phase boundary between the threefold superstructure (LaGaH1.66 type) and the onefold structure (NdGaH1.1 type) is estimated on the basis of phase-composition isotherms and neutron powder diffraction to be x = 1.15.

We have prepared and investigated superconducting equimolar medium-entropy alloys of TiZrNb and TiZrNbHf. Their basic superconducting parameters, as the values of the critical temperature T_c, upper critical magnetic field B_c2 and the superconducting energy gap Δ have been studied with the use of magnetic susceptibility and point-contact Andreev reflection (PCAR) spectroscopy measurements. Although our samples have different critical temperatures, namely T_c ∼ 8.2 K for TiZrNb and T_c ∼ 6.3 K for TiZrNbHf, their zero-temperature critical magnetic field has the same value B_c2(0) = 12 T, from the vicinity of the Clogston limit. We have observed the presence of degraded phases on the surfaces of all the investigated samples using PCAR measurements. Still, we were able to show that the bulk phase in both systems exhibits BCS weakly coupled superconductivity with 2Δ(0)/k_BT_c ∼ 3.5.

Prussian white (PW), Na_2−xFe[Fe(CN)₆], is an attractive cathode material for sodium-ion batteries due to its porous framework enabling fast sodium-ion extraction and insertion, environmentally safe elements, scalable synthesis, and performance comparable to current lithium-ion technologies. However, PW suffers from large volume changes between rhombohedral and cubic phases during cycling which is suggested to be detrimental over time because of structural degradation and increased ion insertion resistance. In particular, studies on PW hard carbon full cells revealed that most of the capacity is lost from the lower potential plateau, where this phase transition occurs. It is proposed that cycling in a restricted potential range, where the phase transition is avoided, could benefit the cycle lifetime and capacity retention. Here, we show an operando X-ray diffraction study aiming at determining how the structure evolves after prolonged cycling in different restricted potential ranges and how this impacts the cycling stability and capacity fade in PW. No signs of structural degradation were observed independently of the pre-cycling conditions used. In addition, more of the rhombohedral phase and capacity were recovered in the discharged state when a more restricted potential range had been applied. Thus, it was shown that the phase transition and corresponding volume changes have little impact on the capacity fade. Instead, the main source for capacity fade was proved to be sodium inventory loss, especially during the initial cycles, in combination with, to a lesser extent, polarization. This study gives a new perspective on PW-based batteries in that neither volume changes nor phase transitions are detrimental to battery performance. These results aid the development of improved cycling protocols and battery systems comprised of PW where the lifetime of the material is prolonged.

To enhance battery safety, it is of utmost importance to develop non-flammable electrolytes. An emerging concept within this research field is the development of localized highly concentrated electrolytes (LHCEs). This type of liquid electrolyte relies on the concept of highly concentrated electrolytes (HCEs), but possesses lower viscosity, improved conductivity and reduced costs due to the addition of diluent solvents. In this work, two different hydrofluoroethers, i.e., bis(2,2,2-trifluoroethyl) ether (BTFE) and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), are studied as diluents in a phosphate-based non-flammable liquid electrolyte. These two solvents were added to a highly concentrated electrolyte of 3.0 M lithium bis(fluorosulfonyl)imide (LiFSI) in triethyl phosphate (TEP) whereby the salt concentration was diluted to 1.5 M. The solvation structures of the HCE and LHCE were studied by means of Raman spectroscopy and Nuclear Magnetic Resonance (NMR) spectroscopy, where the latter was shown to be essential to provide more detailed insights. By using molecular dynamics simulations, it was shown that a highly concentrated Li+-TEP solvation sheath is formed, which can be protected by the diluents TTE and BTFE. These simulations have also clarified the energetic interaction between the components in the LHCE, which supports the experimental results from the viscosity and the NMR measurements. By performing non-covalent interaction analysis (NCI) it was possible to show the main contributions of the observed chemical shifts, which indicated that TTE has a stronger effect on the solvation structure than BTFE. Moreover, the electrochemical performances of the electrolytes were evaluated in half-cells (Li|NMC622, Li|graphite), full-cells (NMC622|graphite) and Li metal cells (Li|Cu). Galvanostatic cycling has shown that the TTE based electrolyte performs better in full-cells and Li-metal cells, compared to the BTFE based electrolyte. Operando pressure measurements have indicated that no significant amount of gases is evolved in NMC622|graphite cells using the here presented LHCEs, while a cell with 1.0 M LiFSI in TEP displayed clear formation of gaseous products in the first cycles. The formation of gaseous products is accompanied by solvent co-intercalation, as shown by operando XRD, and quick cell failure. This work provides insights on understanding the solvation structure of LHCEs and highlights the relationship between electrochemical performance and pressure evolution.

We have prepared and investigated the superconducting equimolar alloys TiZrNb, TiZrNbHf and TiZrNbHfTa, which exhibit transition temperatures Tc between 6.4 K and 8.4 K, and examined the influence of hydrogenation on their superconductivity. The upper critical magnetic field Hc2 of alloys was estimated to be above 10 T, in agreement with previous studies of superconducting alloys of similar composition. On the other hand, the hy-drogenation of alloys, some of which appear to be promising for hydrogen storage, lead to suppression of su-perconductivity in TiZrNb, TiZrNbHf and TiZrNbHfTa dihydrides and in TiZrNbHfTa monohydride, and no transition to superconducting state was observed therein above 2 K. A possible reason for this may be related to the high concentration of disorder (defects) in hydrides originating from the preparation method during which the starting alloy disintegrates into fine powder.

The ability to rapidly screen material performance in the vast space of high entropy alloys is of critical importance to efficiently identify optimal hydride candidates for various use cases. Given the prohibitive complexity of first principles simulations and large-scale sampling required to rigorously predict hydrogen equilibrium in these systems, we turn to compositional machine learning models as the most feasible approach to screen on the order of tens of thousands of candidate equimolar high entropy alloys (HEAs). Critically, we show that machine learning models can predict hydride thermodynamics and capacities with reasonable accuracy (e.g. a mean absolute error in desorption enthalpy prediction of ∼5 kJ mol_H2⁻¹) and that explainability analyses capture the competing trade-offs that arise from feature interdependence. We can therefore elucidate the multi-dimensional Pareto optimal set of materials, i.e., where two or more competing objective properties can't be simultaneously improved by another material. This provides rapid and efficient down-selection of the highest priority candidates for more time-consuming density functional theory investigations and experimental validation. Various targets were selected from the predicted Pareto front (with saturation capacities approaching two hydrogen per metal and desorption enthalpy less than 60 kJ mol_H2⁻¹) and were experimentally synthesized, characterized, and tested amongst an international collaboration group to validate the proposed novel hydrides. Additional top-predicted candidates are suggested to the community for future synthesis efforts, and we conclude with an outlook on improving the current approach for the next generation of computational HEA hydride discovery efforts.

Nucleation is a fundamental part in most syntheses of ceramic materials. Yet, few techniques enable control of this step, which would offer possibilities to attain full-scale kinetic selectivity of the syntheses to reach novel compounds with unique properties. Herein, we present a nucleation-controlled crystallization pathway to synthesize coatings of aluminum titanate (Al₂TiO₅)─renowned for its low-to-negative thermal expansion─at significantly reduced temperatures than conventional solid-state techniques. Based on a kinetic study using in situ X-ray diffraction, detailed mechanistic insights into the crystallization process and phase evolutions within the Al–Ti–O system are obtained. The lowest activation energies for crystallization are given when the Al–Ti ratio is close-to-stoichiometric or Ti-enriched. Along with these compositions’ similar kinetics at the earliest stages of the transformation, a joint nucleation behavior is discovered, revealing the elemental role of titanium in nucleating the main Al₂TiO₅ phase. Based on classical nucleation theory, we deduce the significant influence of the configurational entropy (S_config) when crystallization occurs in the nucleation-controlled domain. Finally, peculiar transition features are observed in the Al-enriched regime during annealing at intermediate temperatures, whose causes are ascribed to the presence of secondary nucleation events and possibilities of structural relaxations in the amorphous matrixes when crystallizing.