Anionic Sublattices in Halide Solid Electrolytes: A Case Study with the High-Pressure Phase of Li3ScCl6.

The Li3MX6 compounds (M=Sc, Y, In; X=Cl, Br) are known as promising ionic conductors due to their compatibility with typical metal oxide cathode materials. In this study, we have successfully synthesized γ-Li3ScCl6 using high pressure for the first time in this family. Structural analysis revealed that the high-pressure polymorph crystallizes in the polar and chiral space group P63mc with hexagonal close-packing (hcp) of anions, unlike the ambient-pressure α-Li3ScCl6 and its spinel analog with cubic closed packing (ccp) of anions. Investigation of the known Li3MX6 family further revealed that the cation/anion radius ratio, rM/rX, is the factor that determines which anion sublattice is formed and that in γ-Li3ScCl6, the difference in compressibility between Sc and Cl exceeds the ccp rM/rX threshold under pressure, enabling the ccp-to-hcp conversion. Electrochemical tests of γ-Li3ScCl6 demonstrate improved electrochemical reduction stability. These findings open up new avenues and design principles for lithium solid electrolytes, enabling routes for materials exploration and tuning electrochemical stability without compositional changes or the use of coatings.

Li-Ion Conductivity and Phase Stability of Ca-Doped LiBH4 under High Pressure.

The effect of Ca doping on the Li-ion conductivity and phase stability of the rock-salt-type LiBH4 phase emerging under high pressures in the range of gigapascals has been investigated. In situ electrochemical measurements under high pressure were performed using a cubic-anvil-type apparatus. Ca doping drastically enhanced the ionic conductivity of the rock-salt-type phase: the ionic conductivity of undoped and 5 mol %Ca-doped LiBH4 was 2.2 × 10-4 and 1.4 × 10-2 S·cm-1 under 4.0 GPa at 220 °C, respectively. The activation volume of LiBH4-5 mol %Ca(BH4)2, at 3.2 cm3·mol-1, was comparable to that of other fast ionic conductors, such as lithium titanate and NASICONs. Moreover, Ca-doped LiBH4 showed lithium plating-stripping behavior in a cyclic voltammogram. These results indicate that the conductivity enhancement by Ca doping can be attributed to the formation of a LiBH4-Ca(BH4)2 solid solution; however, the solid solution decomposed into the orthorhombic LiBH4 phase and the orthorhombic Ca(BH4)2 phase after unloading the high pressure.

Dissociative Oxygen Adsorption and Incorporation in Co3O4-Dispersed BaZr0.9Sc0.1O2.95 for PCFC Cathode.

The development of air electrodes with superior surface oxygen exchange properties at intermediate temperatures is crucial for improving the efficiency of protonic ceramic fuel cells. This study evaluated the surface exchange properties of Co3O4 dispersed protonic conductors, BaZr0.9Sc0.1O2.95. Although Co3O4 is widely acknowledged as superior dissociative adsorption catalysts, there is still ambiguity regarding the enhancement mechanisms of their surface exchange properties by Co3O4, as well as their optimal composition to achieve high catalytic activity. To overcome these difficulties, this study elucidated the effect of the chemical states and composition of composites on their surface exchange properties by evaluating their chemical states and surface exchange reaction rates with several compositions prepared at different temperature conditions using a vibrating-sample magnetometer and the pulse isotope exchange technique. For samples annealed at a high temperature, it became evident that the surface exchange activity became the most active by adding only 1 vol % Co3O4 and indicated an abrupt decline above this composition despite an increase in the volume of the catalysts. This was attributed to the combined effect of the high dissociative adsorption activity of the Co-containing solid solutions formed at a high temperature and a decrease in oxygen vacancies due to hole compensation. For samples annealed at intermediate temperature, their chemical states remained unchanged from those of the original milled powders, and their surface exchange properties monotonically improved with an increase in the volume of Co3O4. Based on the results, different chemical states of composites derived from different preparation conditions lead to completely different activation behavior of the surface exchange reaction.

Key Role of Interfacial Cobalt Segregation in Stable Low-Resistance Composite Oxygen-Reducing Electrodes.

The development of efficient and stable oxygen-reducing electrodes is challenging but vital for the production of efficient electrochemical cells. Composite electrodes composed of mixed ionic-electronic conducting La1-xSrxCo1-yFeyO3-δ and ionic conducting doped CeO2 are considered promising components for solid oxide fuel cells. However, no consensus has been reached regarding the reasons of the good electrode performance, and inconsistent performance has been reported among various research groups. To mitigate the difficulties related to analyzing composite electrodes, this study applied three-terminal cathodic polarization to dense and nanoscale La0.6Sr0.4CoO3-δ-Ce0.8Sm0.2O1.9 (LSC-SDC) model electrodes. The critical factors determining the performance of the composite electrodes are the segregation of catalytic cobalt oxides to the electrolyte interfaces and the oxide-ion conducting paths provided by SDC. The addition of Co3O4 to the LSC-SDC electrode resulted in reduced LSC decomposition; thus, the interfacial and electrode resistances were low and stable. In the Co3O4-added LSC-SDC electrode under cathodic polarization, Co3O4 turned wurtzite-type CoO, which suggested that the Co3O4 addition suppressed the decomposition of LSC and, thus, the cathodic bias was maintained from the electrode surface to electrode-electrolyte interface. This study shows that cobalt oxide segregation behavior must be considered when discussing the performance of composite electrodes. Furthermore, by controlling the segregation process, microstructure, and phase evolution, stable low-resistance composite oxygen-reducing electrodes can be fabricated.

Heat-Resistant Black Insulative Thin Films for Flat-Panel Displays in Al-Doped Ag-Fe-O Systems.

Multilayer antireflection (AR) coatings require a material with a large and constant absorption coefficient over the whole visible range and thermal stability. Coatings for use in touch panel displays are also required to be electrically insulative. In this study, 60 mol % Ag-40 mol % (Fe1-xAlx)-O (x = 0, 0.25, 0.50, 0.75, and 1.0) thin films are prepared by pulsed laser deposition, and their optical properties, electric resistance, and thermal stability are clarified by combining the experimental data and density functional theory (DFT) calculations. Over the visible range, large and constant absorption coefficients are obtained for all compositions. The standard deviations of the absorption coefficients of the x = 0.75 and 1.0 samples are found to be smaller than those of conventional materials like graphite and CrOx. High sheet resistance (Rsheet > 107 Ω·sq-1) is also confirmed. It is determined that nanometer-sized Ag dispersed into a matrix, which was confirmed to be ionic Ag in the matrix phase, is responsible for the absorption at a shorter visible light range and insulative nature even at high Ag content. The films with high Al content are stable up to 500 °C. The potential of these black insulative Ag-Al-Fe-O thin films for use as black AR coatings is confirmed by optical simulations with multilayer stacks.

Hydride-based antiperovskites with soft anionic sublattices as fast alkali ionic conductors.

Most solid-state materials are composed of p-block anions, only in recent years the introduction of hydride anions (1s2) in oxides (e.g., SrVO2H, BaTi(O,H)3) has allowed the discovery of various interesting properties. Here we exploit the large polarizability of hydride anions (H-) together with chalcogenide (Ch2-) anions to construct a family of antiperovskites with soft anionic sublattices. The M3HCh antiperovskites (M = Li, Na) adopt the ideal cubic structure except orthorhombic Na3HS, despite the large variation in sizes of M and Ch. This unconventional robustness of cubic phase mainly originates from the large size-flexibility of the H- anion. Theoretical and experimental studies reveal low migration barriers for Li+/Na+ transport and high ionic conductivity, possibly promoted by a soft phonon mode associated with the rotational motion of HM6 octahedra in their cubic forms. Aliovalent substitution to create vacancies has further enhanced ionic conductivities of this series of antiperovskites, resulting in Na2.9H(Se0.9I0.1) achieving a high conductivity of ~1 × 10-4 S/cm (100 °C).

(45)Sc NMR spectroscopy and first-principles calculation on the symmetry of ScO6 polyhedra in BaO-Sc2O3-based oxides.

The correlation between the local structure and the electric-field gradient at the Sc site in ScO6 polyhedra in Sc2O3, Ba3Sc4O9 and BaSc2O4 was investigated by means of (45)Sc NMR spectroscopy and DFT calculations. The electric-field gradient at the nucleus as determined experimentally and by calculations is compared using the quadrupolar coupling constant, CQ, around chemically and crystallographically distinct Sc sites in Sc-containing compounds. With CQ as the NMR parameter, the results obtained from the DFT calculation were in good agreement with the NMR measurements. The increase in the CQ values with the standard deviation of the O-O bond length surrounding Sc indicates that CQ is affected by the distribution of the six nearest neighboring O atoms around Sc. This study suggests that CQ plays an important role as an indicator of the local structure around ions, and that a combined complementary approach using both NMR spectroscopy and DFT calculation can be used along with diffraction techniques to provide a detailed understanding of crystal structures.