The simultaneous presence of hydride (H-) and oxide (O2-) anions in an inorganic material is thermodynamically challenging. Oxyhydrides have always been synthesized from an oxide precursor, by using high-temperature solid-state reaction using a mixture of oxide and hydride, topochemical reduction at mild temperatures, or high-pressure synthesis. Here, we introduce a novel and unprecedented synthesis route for transition metal oxyhydrides, where the starting material is not an oxide but an intermetallic compound, LaScSi. The topochemical synthesis of LaScSiOxHy (x ≈ 0.5, y ≈ 1) occurs through water dissociation, highlighting the exceptional catalytic behavior of the electride-type parent material. The topochemical insertion of oxygen and hydrogen transforms LaScSi into a more two-dimensional material and modifies its electronic properties, altering its transport properties, from three-dimensional metallic to semimetallic. This innovative path to oxyhydrides is also of fundamental interest for catalysis: it could open the way for new methods of hydrogen production and storage, especially in water splitting, bypassing traditional processes such as electrolysis or photocatalysis.

We report a comparative study of two cerium-based intermetallic compounds: CeFeSi with an anti-PbFCl type structure, and CeFeSiH with a ZrCuSiAs type structure. The latter is obtained from CeFeSi through hydrogen insertion. Our results are based on x-rays, transport, thermodynamic and magnetic measurements. While the tetragonal structure withP4/nmmsymmetry remains unchanged after hydrogen insertion, the thermodynamic, magnetic, and transport properties change drastically. On the one hand, CeFeSi behaves as a Pauli paramagnet with a small Sommerfeld coefficient, indicating the absence of 4felectron physics. On the other hand, our study shows that CeFeSiH exhibits strong magnetic fluctuations with a magnetic transition at 3.5 K, and coherent Kondo-lattice heavy-fermion features.

Topochemical reactions in transition metal oxides, typically involving oxygen removal or anion exchange, provide a versatile platform for creating metastable phases with diverse functionalities. While these reactions often modify the valence and coordination environment of transition metals, the underlying metal frameworks are usually preserved, maintaining a 1:1 structural correspondence. A representative example is SrFeO3 → SrFeO2, in which each octahedral layer transforms into a single square-planar layer. In this study, we report an unprecedented topochemical transformation in Mo2Ta2O11, composed of alternating MoO4 tetrahedral bilayers and TaO6 octahedral bilayers. Ammonolysis at 500 °C in the presence of Mo(CO)6 collapses the MoO4 tetrahedral bilayer into a single MoO6 octahedral layer, thereby breaking the conventional 1:1 structural correspondence. This collapse leads to an 18% contraction along the c axis, substantially exceeding the 10% contraction seen in SrFeO2. The resulting compound, Mo3Ta2O10N (space group R-3m), has an Mo-based kagomé lattice with finite d-electrons (Mo4.33+), in sharp contrast to the d0 configuration of the precursor (Mo6+2Ta5+2O11). Magnetic susceptibility and NMR measurements suggest that Mo3Ta2O10N is an itinerant kagomé system. This study demonstrates that topochemical reactions can induce dynamic and extensive structural reorganizations, pushing the boundaries of what was previously considered accessible by such low-temperature routes.

We report the synthesis of bulk RE1-x A x NiO3 (RE = La, Nd; A = Sr, Ca) perovskite phases under high oxygen pressure (T = 900 degrees C, P O2 = 250 bar) and identify a solubility limit of x = 0.07 for phase-pure samples. This solubility limit, shared by the various RE and A combination investigated, is likely constrained by the Ni4+ content (t 2g 6) whose electronic effect limits doping, regardless the size of RE and A atoms. Alkaline earth (hole) doping induces a decrease in the volume of the unit cell of RE1-x A x NiO3, despite the presence of larger alkaline earth atoms, and an increase in the orthorhombic distortion in the case of RE = Nd (Nd1-x A x NiO3). After topotactic reduction, RE1-x Sr x NiO2 infinite-layers were obtained by mixing the perovskite phase with 2 mol CaH2 in a tube sealed under secondary vacuum and treated at low temperature (250 degrees C). Thermogravimetric analysis was used to determine the oxygen stoichiometries of the compounds with accuracy. We find that while the perovskite parent compound RENiO3 displays a high crystalline quality, regardless the nature of the rare-earth (Nd or La), marked stacking faults are present in the reduced NdNiO2 infinite-layer, as determined by X-ray diffraction measurements using synchrotron radiation. The high-pressure diffraction experiment further demonstrates the role of pressure in attenuating the effect of these stacking faults that were also partially simulated and modeled using the FAULTS program. These defects are virtually absent for Sr2+ doping at 7% or when Nd is replaced by La. The occurrence of such stacking faults is confirmed by HRTEM analysis in the case of NdNiO2. These stacking faults are more pronounced in the reduced infinite layer compositions for which the parent perovskite structure is more distorted, as measured by the departure of the Ni-O-Ni angle from 180 degrees, establishing therefore a memory effect between the distortion of the perovskite structure and the occurrence of stacking faults after reduction. The more the perovskite structure is distorted, the greater the stacking fault rate. Finally, we report and discuss the magnetic properties, the electrical resistivity, and the specific heat of La and Nd-based infinite layer compositions with respect to their structural properties. More specifically, we shed light on the contribution of f-electrons of Nd3+ to the specific heat and discuss the possible signature of spin glass state in LaNiO2 through magnetic and specific heat measurements.

Uniaxial pressure provides an efficient approach to control the competition between charge density waves (CDWs) and superconductivity in underdoped YBa$_{2}$Cu$_{3}$O$_{\rm{y}}$. It can enhance the correlation volume of ubiquitous short-range 2D CDW correlations, and induces a long-range 3D CDW otherwise only accessible at large magnetic fields. Here, we use x-ray diffraction to study the strain and doping evolution of these CDWs. No signatures of discommensurations nor pair density waves are observed in the investigated strain-temperature parameter space, but direct evidence for a form of competition between 2D and 3D CDWs is uncovered. We show that the interplay between the 3D CDW, the 2D CDWs and superconductivity is qualitatively well described by including strain effects in simulations of a nonlinear sigma model of competing superconducting and CDW orders. From a broader perspective, our results underscore the potential of strain tuning as a powerful tool for probing and manipulating competing orders in quantum materials.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Intermetallics represent an important family of compounds, in which insertion of light elements (H, B, C, N) has been widely explored for decades to synthesize novel phases and promote functional materials such as permanent magnets or magnetocalorics. Fluorine insertion, however, has remained elusive so far since the strong reactivity of this atypical element, the most electronegative one, tends to produce the chemical decomposition of these systems. Here, we introduce a topochemical method to intercalate fluorine atoms into intermetallics, using perfluorocarbon reactant with covalent C-F bonds. We demonstrate the potential of this approach with the synthesis of non-stoichiometric mixed anion (Si-F) LaFeSiFx single-crystals, which are further shown to host FeSi-based superconductivity. Fluorine topochemistry on intermetallics is thus proven to be an effective route to provide functional materials where the coexistence of ionic and metallo-covalent blocks, and their interactions through inductive effects, is at the root of their functional properties.

Multilayered cuprates possess not only the highest superconducting temperature transition but also offer a unique platform to study disorder-free CuO2 planes and the interplay between competing orders with superconductivity. Here, we study the underdoped trilayer cuprate HgBa2Ca2Cu3O8+δ and we report quantum oscillation and Hall effect measurements in magnetic field up to 88 T. A careful analysis of the complex spectra of quantum oscillations strongly supports the coexistence of an antiferromagnetic order in the inner plane and a charge order in the outer planes. The presence of an ordered antiferromagnetic metallic state that extends deep in the superconducting phase is a key ingredient that supports magnetically mediated pairing interaction in cuprates.

Electronic synergy between metal ions and organic linkers is a key to engineering molecule-based materials with a high electrical conductivity and, ultimately, metallicity. To enhance conductivity in metal-organic solids, chemists aim to bring the electrochemical potentials of the constituent metal ions and bridging organic ligands closer in a quest to obtain metal- d and ligand- π admixed frontier bands. Herein, we demonstrate the critical role of the metal ion in tuning the electronic ground state of such materials. While VCl 2 (pyrazine) 2 is an electrical insulator, TiCl 2 (pyrazine) 2 displays the highest room-temperature electronic conductivity (5.3 S cm –1 ) for any metal-organic solid involving octahedrally coordinated metal ions. Notably, TiCl 2 (pyrazine) 2 exhibits Pauli paramagnetism consistent with the specific heat, supporting the existence of a Fermi liquid state (i.e., a correlated metal). This result widens perspectives for designing molecule-based systems with strong metal-ligand covalency and electronic correlations.

HgBa2Ca2Cu3O8+δ V. Oliviero1,†, S. Benhabib1,†,‡,∗, I. Gilmutdinov, B. Vignolle, L. Drigo , M. Massoudzadegan, M. Leroux, G.L.J.A. Rikken, A. Forget, D. Colson, D. Vignolles1,∗ and C. Proust1,∗ LNCMI-EMFL, CNRS UPR3228, Univ. Grenoble Alpes, Univ. Toulouse, INSA-T, Grenoble and Toulouse, France Institut de Chimie de la Matière Condensée, Bordeaux, France Service de Physique de l’Etat Condensé, CEA Saclay (CNRS-URA 2464), Gif sur Yvette 91191, France

Clément Collignon, 2, ∗ Yudai Awashima, Ravi, Xiao Lin, † Carl Willem Rischau, ‡ Anissa Acheche, Baptiste Vignolle, 5 Cyril Proust, Yuki Fuseya, 6 Kamran Behnia, and Benoit Fauqué § JEIP, USR 3573 CNRS, Collège de France, PSL Research University, 11, place Marcelin Berthelot, 75231 Paris Cedex 05, France Laboratoire de Physique et d’Étude des Matériaux (ESPCI Paris CNRS Sorbonne Université), PSL Research University, 75005 Paris, France Department of Engineering Science, University of Electro-Communications, Chofu, Tokyo 182-8585, Japan Laboratoire National des Champs Magnétiques Intenses (LNCMI-EMFL), CNRS ,UGA, UPS, INSA, Grenoble/Toulouse, France Institut de Chimie de la Matière Condensée, Bordeaux, France Institute for Advanced Science, University of Electro-Communications, Chofu, Tokyo 182-8585, Japan (Dated: January 25, 2021)

High-T-c cuprate superconductors host spin, charge, and lattice instabilities. In particular, in the antiferromagnetic glass phase, over a large doping range, lanthanum-based cuprates display a glass-like spin freezing with antiferromagnetic correlations. Previously, sound velocity anomalies in La1.88Sr0.12CuO4 (LSCO) for hole doping p = x >= 0.145 were reported and interpreted as arising from a coupling of the lattice to the magnetic glass [M. Frachet, I. Vinograd et al., Nat. Phys. 16, 1064 (2020)]. Here we report both sound velocity and attenuation in LSCO p = 0.12, i.e., at a doping level for which the spin freezing temperature is the highest. Using high magnetic fields and comparing with nuclear magnetic resonance measurements, we confirm that the anomalies in the low temperature ultrasound properties of LSCO are produced by a coupling between the lattice and the spin glass. Moreover, we show that both sound velocity and attenuation can be simultaneously accounted for by a simple phenomenological model originally developed for canonical spin glasses. Our results point towards a strong competition between superconductivity and spin freezing, tuned by the magnetic field. A comparison of different acoustic modes suggests that the slow spin fluctuations have a nematic character.