The Na-Ga phase diagram was reinvestigated by heat-flux differential scanning calorimetry (HF-DSC) and powder X-ray diffraction (PXRD). The most sodium-rich phase, Na22Ga39, melts congruently (549(2) °C), while Na7Ga13 (545(2) °C), Na2Ga7 (501(2) °C), and NaGa4 (495(2) °C) decompose peritectically. In the sodium-rich region, a monotectic reaction between Na22Ga39 and melt occurs at 495(2) °C. The critical temperature of the liquid two-phase region was estimated to 523(2) °C. The subtle differences in the decomposition temperatures of neighboring phases were resolved by differential thermal analysis using a mutual sample reference method.

Ni5.7SnSe2, the first member (n = 1) of the layered intergrowth series [Ni3Sn] n [Ni4-delta Se2] (delta = 1.3), was synthesized as a dense, single-phase polycrystalline material by optimizing the Ni content through solid-state reaction followed by spark plasma sintering. At room temperature, laboratory powder X-ray diffraction can be attributed to an average tetragonal structure (space group I4/mmm), in agreement with previous reports; however, weak superstructure reflections reveal a deviation from this high-symmetry average description. Through a combined analysis using single-crystal X-ray diffraction, electron microscopy and synchrotron powder diffraction, the structure is unambiguously resolved in monoclinic symmetry, revealing long-range ordering between the occupied and empty Ni sites within the [Ni4-delta Se2] layers. Variable-temperature synchrotron powder diffraction demonstrates that the superstructure reflections and the associated monoclinic peak splitting vanish reversibly above 490 K, indicating an order-disorder structural transition. Electron diffraction and high-angle annular dark-field scanning transmission electron microscopy further confirm the monoclinic symmetry at room temperature, and reveal the presence of stacking faults along the stacking direction of the layers. Electrical transport measurements indicate metallic behavior (rho = 0.08 m Omega cm at 300 K, RRR approximate to 4.5) and reveal a sharp, reversible anomaly in both resistivity and Seebeck coefficient at the transition temperature, establishing a strong coupling between Ni ordering and electronic transport.

We carried out nonresonant inelastic x-ray scattering measurements at the V L_{1} edge to probe the local V 3d charge density in VO_{2} across the metal-insulator transition (MIT). Without relying on spectral calculations, we were able to integrate directly from the orientational dependence an image of the occupied 3d shell and extract quantitatively the orbital occupations of the V ions. We found that in the low-temperature insulating M_{1} phase the V is highly polarized toward the σ configuration. The orbital occupation undergoes significant redistribution upon transition into the metallic R phase, leading to a more isotropic charge density. The massiveness of the orbital switching promotes the scenario in which electron correlations and lattice degrees of freedom are strongly coupled, so that the contribution of the lattice and the electronic part to the energetics must be treated on equal footing to model the MIT quantitatively.

The cage compound BaIr 2 Si 9 adopts the BaRh 2 Si 9 structure type with space group C 2/ c (Pearson symbol mC 48, a = 6.230(1) Å, b = 21.409(3) Å, c = 6.232(1) Å, β = 90.30(1)°). The atomic arrangement features fragmented sodalite cages that are interrupted along [010] by puckered Ir–Si layers showing the pentagonal Cairo‐Tiling motif. The compound melts incongruently at 1180°C and is obtained as a single‐phase after annealing at 800°C for 3 days. Electric transport measurements reveal that BaIr 2 Si 9 is a p ‐type semiconductor, consistent with band structure calculations indicating a bandgap of 0.5 eV. Quantum chemical calculation confirms positively charged Ba atoms accompanied by Ir atoms with negative charges. The charge distribution of silicon is heterogeneous as Si atoms bonded to Ir exhibit positive charges while those forming merely Si–Si contacts are negatively charged.

The search for intermetallic compounds with elements providing strong spin-orbit coupling yields the new phase Mg3BiN adopting a cubic (anti-)perovskite-type crystal structure (a = 4.4011(2) & Aring;). Synthesis is performed at high-pressure high-temperature conditions in a Walker-type large volume device (8 GPa, 1123-1273 K). The ternary compound is formed by reaction of Mg-Bi mixtures with the crucible material boron nitride upon prolonged heating for 2 hours. The position of the nitride anion is identified by analysis of the spatial distribution of the electron localizability indicator in the metal matrix. The electron balance [Mg+2]3[Bi-3][N-3] indicates that the compound is electron-precise in accordance with the Zintl concept, and the calculated electronic density of states indicates semiconducting properties.

Li2ZnSi is a layered Zintl phase composed of heterographene-like Zn-Si sheets separated by Li atoms. Although the intrinsic crystal structure is fully ordered, mechanical handling readily introduces stacking faults of the Zn-Si layers. These defects significantly broaden the 7Li and 29Si NMR signals and are described by statistically disordered structure models in single-crystal X-ray diffraction. Upon moderate heating to only 310-370 K, the 7Li NMR spectra sharpen, while single-crystal X-ray diffraction reveals a fully ordered structure model. The heat-capacity data exhibit a broad endothermic feature during heating, characteristic of a stress-relief annealing process rather than a thermodynamic phase transition. Mechanical treatment strongly affects physical properties, and the transport response in impedance measurements is dominated by grain-boundary effects. Density-functional calculations show that the stacking-fault formation is energetically unfavorable but localized, explaining why the defects are readily introduced mechanically and can be healed at unexpectedly low temperatures.

We performed the Te-nuclear magnetic resonance, the Mo-nuclear quadrupole resonance, and the AC susceptibility in the Weyl semimetal superconductor 1T-MoTe2 at pressures up to 2.17 GPa. From the temperature and pressure dependence of the AC susceptibility, the superconducting transition temperature Tc and the upper critical field Hc2 were estimated. The results deviate from the Werthamer-Helfand-Hohenberg model but are well described by Hc2(T) = Hc2(0)[1-T/Tc]alpha. The latter fit yields Hc2(0) = 1.50 T, Tc= 3.81 K, and alpha = 1.1 at 2.17 GPa, suggesting that the superconductivity lies in a strong-coupling regime. Since the nuclear spin-lattice relaxation rate divided by temperature, 1/T1T, follows the Korringa relation at ambient pressure, the increase in 1/T1T with pressure up to approximately 0.7 GPa indicates an increase in the density of states (DOS), N(EF). This trend mirrors the pressure dependence of Tc in the low-pressure region, consistent with the BCS mechanism. Above 0.7 GPa, however, N(EF) slightly decreases while Tc continues to rise, suggesting an additional pairing contribution beyond the conventional BCS picture. In the 1TA phase at 2.17 GPa, the absence of a coherence peak in 1/T1T around Tc, accompanied by a two-step decrease just below Tc, was observed, which may be a signature of unconventional superconductivity.

Using infrared and Raman spectroscopies combined with high-resolution x-ray diffraction, we address several controversial aspects of altermagnetic alpha-MnTe. We show that mechanical stress applied to crystals of this material causes a drastic broadening of Bragg peaks that conceals signatures of additional phases present in the sample. Indeed, spatially resolved Raman spectroscopy reveals that the modes around 175 cm-1 often reported in alpha-MnTe are not reproducible across different positions and samples and originate from the secondary phase of MnTe2. By combining spectroscopic probes with ab initio calculations, we establish the IR-active optical phonon of alpha-MnTe around 155 cm-1 (E1u) and the Raman-active optical phonon around 100 cm-1 (E2g) at room temperature. Two intense Raman modes around 120 and 140 cm-1 are shown to be intrinsic, even though they can not be assigned to P-point optical phonons. These modes couple to magnetic order in alpha-MnTe and also to the transient reflectivity, resulting in coherent oscillations. Both sixfold rotation symmetry and inversion symmetry are preserved in bulk alpha-MnTe within our experimental resolution.

The presence of magnetism in potentially altermagnetic RuO2 has been a subject of intense debate. Using broadband infrared spectroscopy combined with density-functional band-structure calculations, we show that the optical conductivity of RuO2, the bulk probe of its electronic structure, is best described by a nonmagnetic model. The sharp Pauli edge demonstrates the presence of a Dirac nodal line lying 45 meV below the Fermi level. An excellent match between the experimental and plasma frequencies underpins the weakness of electronic correlations. The intraband part of the optical conductivity indicates Fermi-liquid behavior with two distinct scattering rates below 150 K. Fermi-liquid theory also accounts for the temperature-dependent magnetic susceptibility of RuO2 and allows a consistent description of this material as a paramagnetic metal. Published by the American Physical Society 2025

In solid-state compounds, the valence of europium can sometimes be mixed, which is especially favored in structures with several positions for the europium atoms. In this work, we study the Eu-based intermetallic noncentrosymmetric system Eu11-x Hg54+x , which has 65 atoms per unit cell and 4 distinct crystallographic positions for europium and 14 positions for mercury. Our detailed analysis of the magnetism of large single crystals suggests that europium in Eu11-x Hg54+x might be present in two valence states, resulting in a fragile magnetic ground state. Due to the cage-like structure with a large distance between the Eu atoms, those atoms are weakly ferromagnetically coupled and Eu11-x Hg54+x orders at low temperatures, below T 1 = 5.5 K, with a subsequent spin reorientation at T 2 = 4.3 K. There is no sign of magnetic frustration. Interestingly, the magnetic ordering of the europium substructure results in a magnetization pole reversal with a delicate ferrimagnetic ground state. Additional magnetic phases can be induced by the application of a modest external magnetic field.

New TiNiSi-type compounds ALiAu (A = Ca, Sr, Ba, Eu, Yb) were obtained in the form of mm-sized single crystals by high-temperature centrifugation-aided filtration from lithium melt. They are the first examples of TiNiSi-type representatives containing Li and a transition metal. The metallic phases show paramagnetic (Ca) or diamagnetic (Sr, Ba, Yb) behavior or antiferromagnetic ordering below 19 K (Eu). A new structural description is based on a hexagonal close packing with A occupying all octahedral and Li occupying half of the tetrahedral voids in an ordered fashion. Chemical bonding analysis supports the structural description and reveals the formation of eight-atomic stella-quadrangula bonds pinned on the empty tetrahedral holes, a bonding picture known from elemental metals.

Understanding superconductivity requires a deep comprehension of the chemical structure. The discovery of a new unconventional superconductor UTe2 a few years ago prompted many detailed investigations of its physical properties. Despite its unconventional ground state being rather well-studied, a strong sample-to-sample variation of superconducting behavior as a result of different preparation conditions has remained largely unexplained until now. In this work, an in-depth analysis of the UTe2 crystal structure and resultant physical properties by implementing several types of synthetic routes was carried out. The difference between superconducting and non-superconducting UTe2 lies in the presence of uranium vacancies, on the order of 4%. As a result, the b and c lattice parameters vary, yielding a volume difference of about 0.51%. A subtler difference between samples exhibiting one and two superconducting transitions is driven by local deviations from the translational symmetry in the main atomic arrangement. Several well-pronounced maxima have been observed in the difference density map, predominantly located in the bc plane due to a local appearance of the similar atomic arrangements in different orientations. The extreme sensitivity of UTe2 to such a small number of defects re-emphasizes the unconventional nature of superconductivity in this compound. Furthermore, this work underscores the importance of a thorough, combined chemical and physical analysis of intriguing strongly correlated materials─in particular for compounds that are known to exhibit nontrivial ground states and exotic accompanying phenomena.

The pressure evolution of RuO2 is studied using single-crystal x-ray diffraction in a diamond anvil cell, combined with ab initio band-structure calculations. The tetragonal rutile structure transforms into the orthorhombic CaCl2-type structure above 13 GPa under quasihydrostatic pressure conditions. This second-order transition is ferroelastic in nature and accompanied by tilts of the RuO6 octahedra. Orthorhombic RuO2 is expected to be a paramagnetic metal, similar to ambient-pressure RuO2. It shows the increased t2g-eg crystal-field splitting that is responsible for the pressure-induced color change. It further features the Dirac nodal line that shifts across the Fermi level upon compression.

With many candidate altermagnetic materials, MnTe has emerged as one of the most promising systems, with growing experimental evidence for altermagnetic phenomena. So far, the majority of measurements have been performed on thin-films, or have involved surface measurements. However, the question of altermagnetic order in the bulk system - in the absence of substrate or surface effects - remains. Here we show evidence for bulk altermagnetism in single crystal MnTe, through spectroscopic X-ray microscopy. By performing nanoscale X-ray magnetic circular dichroic (XMCD) imaging in transmission on a 200 nm thick lamella, we observe domains and magnetic textures with a spectroscopic signature characteristic of altermagnetic order, thereby confirming the intrinsic nature of altermagnetism in MnTe. Quantitative analysis of the XMCD signal reveals an excellent agreement with predicted signals, establishing that the altermagnetic order exists throughout the thickness of the lamella and confirming the intrinsic, bulk nature of the state. With these results, we demonstrate that transmission XMCD spectroscopic imaging is a robust, quantitative technique to probe altermagnetic order, providing a means to probe individual altermagnetic domains within complex configurations. This ability to investigate, and characterise altermagnetic order in bulk crystals represents an important tool for the exploration of altermagnetism across a wide range of candidate materials, of key importance for the development of future technologies.

The layered Zintl phase Li 2 ZnSi is a structural analog of intercalated graphite with hexagonal layers of Zn and Si atoms separated by Li atoms (space group P 6 3 / mmc , a = 4.2458(2) Å, c = 8.224(1) Å). Single‐crystal X‐ray diffraction reveals Zn relocation into the center of the Zn 3 Si 3 rings in 4% of the hexagonal layers. The Zn relocation is coupled with Li migration. The resulting 2D defects can be modeled either as 60° slab rotations or, alternatively, as layer translations by k = 1/3 [1,−1,0]. Li 2 ZnSi shows metal‐type electrical resistivity (ρ = 1.18 μΩ m at 300 K) and exhibits significantly enhanced diamagnetism, suggesting orbital contributions akin to those in graphite. This study demonstrates transition‐metal mobility in a layered Zintl phase, generating localized 2D defects that leave the local coordination of each atom unchanged. This mechanism is relevant for understanding defect tolerance in structurally related electrode materials.

The preparation of Zintl phases with pronounced spin-orbit coupling has received substantial scientific interest because of their distinctive electronic properties. In the context of superconductivity and topological phenomena related to band inversion, intermetallic compounds of bismuth have come into focus recently. While bismuth forms a rich variety of Zintl phases with the heavier alkaline-earth metals, there are significantly fewer magnesium compounds. Here we show that high-temperature high-pressure synthesis opens a convenient route for the preparation of Mg5Bi3Hx already at moderate conditions. The compound (space group Pnma, a = 11.5399(3) Å, b = 8.9503(2) Å and c = 7.8770(2) Å) adopts a Ca5Sb3F crystal structure. The minute amounts of hydrogen could only be detected by thermal decomposition of the compound in combination with mass spectroscopy of the gas phase. Direct space analysis of the chemical bonding allowed for allocating the hydrogen position at a partially occupied interstitial site and reveals strongly polar Mg-Bi and Mg-H bonds in accordance with the Zintl concept. Calculated band structures exhibit substantial electronic reorganization upon hydrogen insertion. The combination of advanced analytical tools in concert with modern quantum chemical techniques provides an efficient approach to allocate trace amounts of interstitial atoms stabilizing intermetallic phases.

Secondary reactions and solid-electrolyte interface (SEI) formation are crucial aspects for battery lifetime. We show that one part of a natural SEI consists of crystalline NaH, which is formed on the sodium surface when carbonate-based electrolytes are used. Its impact on the electrochemical performance was studied using room-temperature H2-treated Na anodes and a NaH-Na composite anode. Depending on the preparation conditions, hydrogen was stored on the Na surface in the form of NaOH, enhancing the long-term performance of the cell with a layered Na-oxide cathode, or in the form of NaH, deteriorating the performance in comparison to a reference Na cell. With the help of thermogravimetry coupled with mass spectrometry, we identified an explosion-like thermal decomposition of fatigued Na anodes above approximately 120 °C, but H2-treated anodes exhibited higher stability of 10-30 °C compared to the reference anode. The composite NaH-Na anode shows a lower electrochemical capacity but no thermally induced explosion. Therefore, for a highly reactive metallic sodium anode, an effective protective layer against liquid electrolyte components is necessary to achieve high capacities and stable long-term operation. This passivation layer must fulfill the requirement of inertness to hydrogen gas to ensure a long lifetime.

Single crystals of α-MnTe were synthesized by chemical vapor transport using iodine as the transport reagent. Structural characterization by powder x-ray diffraction confirmed the hexagonal structure (space group P6_3/mmc). Magnetization M(T) and specific heat C_p(T) measurements revealed an antiferromagnetic phase transition at T_N ≈307 K. The magnetic entropy derived from the C_p(T) data is consistent with the S = 5/2 spin state of Mn^2+ ions. Angle- and field-dependent magnetization measurements indicate complex magnetic responses associated with domains, and show an anomaly around 1 T. These features are analyzed using a phenomenological micromagnetic model that includes higher-order anisotropic exchange interactions coupling the weak ferromagnetic component and the antiferromagnetic order parameter. The model captures the generic behavior of magnetic states and demonstrates that the observed uniaxial and unidirectional anisotropies arise from metastable domain configurations and irreversible magnetization processes.