The parent Hf(Zr)4Fe2Ox compounds and their saturated deuterides have been synthesized. The crystal structures of Hf2FeD4, Hf4Fe2O0.3D6.34, Hf4Fe2O0.6D3.5, Zr4Fe2O0.25D8.5 and Zr4Fe2O0.5D7.5 using both X-ray and neutron powder diffraction have been determined. Experimental data together with the analysis of the crystal structure of the deuterides indicate that oxygen content influences substantially on H(D)-storage capacity. The interesting phenomenon of local disorder of the metal matrix for the majority of the studied deuterides, which appears at certain concentrations of oxygen and hydrogen, was discovered and analysed. This disorder was in a good agreement with the 57Fe hyperfine data observed at low temperatures for Zr4Fe2O0.25D9.9.

Solid-state sodium ion conductors are crucial for the next generation of all-solid-state sodium batteries with high capacity, low cost, and improved safety. Sodium closo-carbadodecaborate (NaCB11 H12 ) is an attractive Na-ion conductor owing to its high thermal, electrochemical, and interfacial stability. Mechanical milling has recently been shown to increase conductivity by five orders of magnitude at room temperature, making it appealing for application in all-solid-state sodium batteries. Intriguingly, milling longer than 2 h led to a significant decrease in conductivity. In this study, X-ray Raman scattering (XRS) spectroscopy is used to probe the origin of the anomalous impact of mechanical treatment on the ionic conductivity of NaCB11 H12 . The B, C, and Na K-edge XRS spectra are successfully measured for the first time, and ab initio calculations are employed to interpret the results. The experimental and computational results reveal that the decrease in ionic conductivity upon prolonged milling is due to the increased proximity of Na to the CB11 H12 cage, caused by severe distortion of the long-range structure. Overall, this work demonstrates how the XRS technique, allowing investigation of low Z elements such as C and B in the bulk, can be used to acquire valuable information on the electronic structure of solid electrolytes and battery materials in general.

Despite many years of research and continuous improvements in scientific equipment, some of the thermodynamic properties of binary systems are still unknown, or are only theoretically predicted or calculated. This situation often arises from the difficulties in preparing alloys for experimental measurements. The alloys from the Mg-Pd system, especially for the Pd-rich side, are difficult to produce, and the availability of thermodynamic data is very limited. Therefore, this paper presents calorimetric studies on the standard enthalpy of formation of alloys from the Mg-Pd system, which were prepared using mechanical alloying. Three alloys (S1, S2, and S3) were synthesized, homogenized, and subjected to X-ray diffraction (XRD) analysis to investigate their phase composition. The XRD studies showed that the alloys designated as S1 and S2 were the intermetallic phases Mg6Pd and Mg0.9Pd1.1, and the S3 sample was a mixture of MgPd and MgPd3 intermetallic phases. Their heat effects, measured by drop calorimetry, were used to calculate the values of the standard enthalpies of formation of the prepared phases. The values obtained were as follows: −27.5 ± 1.1 kJ/mol at. for the Mg6Pd intermetallic phase, −72.7 ± 1.0 kJ/mol at. for the Mg0.9Pd1.1 intermetallic phase, and −46.8 ± 1.5 kJ/mol at. for the alloy which was a mixture of MgPd and MgPd3. These data were compared with values from the existing literature on the enthalpy of formation of alloys, as well as with data calculated using Miedema’s model.

The ionic conductivity of Li 4 B 10 H 10 B 12 H 12 exceeds that of its parent compounds Li 2 B 10 H 10 and Li 2 B 12 H 12 by several orders of magnitude. It is stable against lithium metal and has been incorporated into solid-state batteries.

Hydroborates are an emerging class of solid electrolytes for all-solid-state batteries. Here, we investigate the impact of pressure on the crystal structure and ionic conductivity of a close-hydroborate salt consisting of Na 2 B 10 H 10 and Na 2 B 12 H 12 . Two Na 2 B 10 H 10 :Na 2 B 12 H 12 ratios were studied, 1:1 and 1:3. The anions of the as-synthesized powder with 1:1 ratio crystallize in a single face-centered cubic phase, while the anions of the powder with 1:3 ratio crystallize in a single monoclinic phase. After applying pressure to densify the powder into a pellet, a partial phase transformation into a body-centered cubic (BCC) phase is observed for both ratios. The BCC content saturates at 50 weight percent (wt%) at 500 MPa for the 1:1 ratio and at 77 wt% at 1000 MPa for the 1:3 sample. The room temperature sodium-ion conductivity follows an analogous trend. For the 1:1 ratio, it increases from 2 × 10 –4 Scm −1 at 10 wt% BCC content to about 1.0 × 10 –3 Scm −1 at 50 wt% BCC content. For the 1:3 ratio, it increases from 1.3 × 10 –5 Scm −1 at 11.9 wt% BCC to 8.1 × 10 –4 Scm −1 at 71 wt% BCC content. Our results show that pressure is a prerequisite to achieve high sodium-ion conductivity by formation of the highly conductive BCC phase.

Thermal polymorphism in the alkali-metal salts incorporating the icosohedral monocarba-hydridoborate anion, CB11H12−, results in intriguing dynamical properties leading to superionic conductivity for the lightest alkali-metal analogues, LiCB11H12 and NaCB11H12. As such, these two have been the focus of most recent CB11H12− related studies, with less attention paid to the heavier alkali-metal salts, such as CsCB11H12. Nonetheless, it is of fundamental importance to compare the nature of the structural arrangements and interactions across the entire alkali-metal series. Thermal polymorphism in CsCB11H12 was investigated using a combination of techniques: X-ray powder diffraction; differential scanning calorimetry; Raman, infrared, and neutron spectroscopies; and ab initio calculations. The unexpected temperature-dependent structural behavior of anhydrous CsCB11H12 can be potentially justified assuming the existence of two polymorphs with similar free energies at room temperature: (i) a previously reported, ordered R3 polymorph stabilized upon drying and transforming first to R3c symmetry near 313 K and then to a similarly packed but disordered I43d polymorph near 353 K and (ii) a disordered Fm3 polymorph that initially appears from the disordered I43d polymorph near 513 K along with another disordered high-temperature P63mc polymorph. Quasielastic neutron scattering results indicate that the CB11H12− anions in the disordered phase at 560 K are undergoing isotropic rotational diffusion, with a jump correlation frequency [1.19(9) × 1011 s−1] in line with those for the lighter-metal analogues.

Closo-Hydroborate Solid Electrolyte The solid electrolyte Na4(CB11H12)2(B12H12) at the interface with Na anode is tested as a function of battery stack pressure and current density in article number 2101254 by Matteo Brighi, Fabrizio Murgia, and Radovan Černý. Employing two different polyanions allows tuning locally the electrochemical properties while preserving structural and chemical coherence. Image credit: Xavier Ravinet & Olivier Gaumer - University of Geneva.

The crystal structures of three thermal polymorphs (I, II, and III) for each isomer of closo-dicarbadodecaboranes C2B10H12 (ortho, meta, and para) have been determined by combining synchrotron radiation X-ray powder diffraction and density functional theory calculations. The structures are in agreement with previous calorimetric and spectroscopic studies. The difference between rotatory phases (plastic crystals) I and II lies in isotropic rotations in the former and anisotropic rotations of the icosahedral clusters in the latter. Phase I is the cubic close packing (ccp) of rotating closo-molecules C2B10H12 in the space group Fm3̅. Phase II is the ccp of rotating closo-molecules C2B10H12 in the cubic space group Pa3̅. The preferred rotational axis in II varies with the isomer. The ordered phases III are orthorhombic (meta) or monoclinic (ortho and para) deformations of the cubic unit cell of the disordered phases I and II. The ordering in the phase III of the ortho-isomer carrying the biggest electrical dipole moment creates a twofold superstructure w.r.t. the cubic unit cell. The thermal polymorphism for C2B10H12 and related metal salts can be explained by division of the cohesive intercluster interactions into two categories (i) dispersive cohesive interaction with additional Coulombic components in the metal salts and (ii) anisotropic local interaction resulting from nonuniform charge distribution around icosahedral clusters. The local interactions are averaged out by thermally activated cluster dynamics (rotations and rotational jumps) which effectively increase the symmetry of the cluster. The C2B10H12 molecules resist at least as well as the CB11H12- anion to the oxidation, and both clusters form easily a mixed compound. This allows designing solid electrolytes such as Nax(CB11H12)x(C2B10H12)1-x, where the cation content may be varied and the temperature of transition into the disordered conducting phase is decreased.

Sodium chromium oxide, NaCrO2, has received significant attention as positive electrode (cathode) for Na-ion batteries mainly due the high capacity retention of the material. In this paper, we use operando powder X-ray diffraction to investigate the structural evolution of O3–NaCrO2 during Na-ion extraction and insertion with use of both liquid and solid-state electrolytes. This reveals a previously overlooked phase transition, causing formation of an unexplored O′3-NaxCrO2 intermediate during Na-ion extraction (charge). The phase transitions within the electrode are investigated by sequential Rietveld refinement and distortion analysis, which shows that the discovered O′3-NaxCrO2 intermediate accommodates the increasing interlayer repulsion and in-plane contraction with less distortion of the [NaO6]-polyhedra as compared to the other observed phases. Our structural findings are corroborated by analysis of the Na-ion diffusion coefficients through the galvanostatic intermittent titration technique. Furthermore, the operando powder X-ray diffraction reveals substantial charge-discharge asymmetry with a significant preference for solid-solution and two-phase behavior during charge (Na-extraction) and discharge (Na-insertion), respectively.

Stack pressure and mechanical robustness are two important parameters needed to tackle the interfacial instability of solid‐state batteries. Here, the mechanical behavior of Na 4 (CB 11 H 12 ) 2 (B 12 H 12 ), as solid electrolyte at the interface with Na anode, is reported. The solid electrolyte is tested as function of stack pressure and different current densities, revealing a critical current density of 0.6 mA cm −2 at room temperature and an optimal stack pressure of 1.5 MPa. These findings are achieved, thanks to the adoption of a multilayer approach, demonstrating the powerfulness of hydroborates to compensate chemical and electrochemical instability, simply employing different complex hydride polyanions that change locally the electrochemical properties while preserving structural and chemical coherence.

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.

This work describes temperature-induced crystallization processes and reaction mechanisms occurring in the borohydride-imidazolate system. In the course of thermal evolution, crystal structures of two novel bimetallic imidazolates AMnIm3 (A = Na, K) were solved using synchrotron radiation powder diffraction data. Both the alkali metal cation and the Mn cations exhibit distorted octahedral coordination while each imidazolate is surrounded by two alkali metal and two manganese atoms. Extensive study of the thermal expansion behaviour revealed that the expansion of the bimetallic imidazolates does not proceed uniformly over the entire temperature range but rather abruptly changes from a colossal negative to a moderate positive volume expansion. Such behaviour is caused by the coherent intergrowth of the coexisting phases which form a composite, a positive lattice mismatch and a tensile strain during the coexistence of NaMIm3 (M = Mg and Mn) and NaIm or HT-NaIm. Such coherent coalescence of two materials opens the possibility for targeted design of zero thermal expansion materials. Crystal structures of AMnIm3 (A = Na, K) were determined. Coherently intergrown NaMIm3/NaIm (M = Mg, Mn) present colossal negative thermal expansion.

The last twenty years of an intense research on metal hydroborates as solid hydrogen stores and solid electrolytes are reviewed. It is shown that from the most promising application in hydrogen storage due to their high gravimetric and volumetric capacities, the focus has moved to solid electrolytes due to high cation mobility in disordered structures with rotating or tumbling anions-hydroborate clusters. Various strategies of overcoming the strong covalent bonding of hydrogen in hydroborates for hydrogen storage and disordering their structures at room temperature for solid electrolytes are discussed. The important role of crystal chemistry and crystallography knowledge in material design can be read in the cited literature.

A new type of hybrid compound, combining properties of MOFs and borohydrides, was synthesized solvothermally using Mg(BH4)2 and imidazole as precursors. Material in the form of acetonitrile solvate with formula [Mg3{(Im)BH2(Im)}6(ImH)6]·CH3CN crystallizes in the space group R3̅, having the unit cell parameters a = 15.1942(2) Å and c = 28.3157(3) Å as determined by single crystal X-ray diffraction. The structure was further investigated by solid-state NMR and DFT quantum chemical calculations. The main feature of the structure, reported here for the first time, is a linear trinuclear complex, where octahedrally nitrogen-coordinated Mg2+ ions are bridged with {(Im)BH2(Im)}- units, forming inside voids of 4.6 Å in diameter between the magnesium ions. Polar intermolecular interactions hold the molecules in a dense rhombohedral stacking, where a disordered acetonitrile molecule plays a cohesive role. The compound is stable in air and upon heating to about 160 °C. Using an alternative synthesis method from an imidazole melt, an imidazole solvate with the formula [Mg3{(Im)BH2(Im)}6(ImH)6]·ImH and a very similar crystal structure to acetonitrile solvate was prepared. It is stable up to 220 °C. Upon further heating, it transformed into a layered structure with the formula Mg(Im3BH)2, space group P3̅1c, and unit cell parameters a = 8.7338(9) Å and c = 17.621(2) Å determined by synchrotron powder diffraction. Besides its structural novelty, two types of potentially reactive hydrogens, bonded to boron and nitrogen in the same molecule, make the material highly interesting for future investigations in the fields of energy storage applications.

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.