Superionic lithium transport via multiple coordination environments defined by two-anion packing

Fast cation transport in solids underpins energy storage. Materials design has focused on structures that can define transport pathways with minimal cation coordination change, restricting attention to a small part of chemical space. Motivated by the greater structural diversity of binary intermetallics than that of the metallic elements, we used two anions to build a pathway for three-dimensional superionic lithium ion conductivity that exploits multiple cation coordination environments. Li 7 Si 2 S 7 I is a pure lithium ion conductor created by an ordering of sulphide and iodide that combines elements of hexagonal and cubic close-packing analogously to the structure of NiZr. The resulting diverse network of lithium positions with distinct geometries and anion coordination chemistries affords low barriers to transport, opening a large structural space for high cation conductivity. </jats:p

Accessing Mg‐Ion Storage in V 2 PS 10 via Combined Cationic‐Anionic Redox with Selective Bond Cleavage

Magnesium batteries attract interest as alternative energy‐storage devices because of elemental abundance and potential for high energy density. Development is limited by the absence of suitable cathodes, associated with poor diffusion kinetics resulting from strong interactions between Mg2+ and the host structure. V2PS10 is reported as a positive electrode material for rechargeable magnesium batteries. Cyclable capacity of 100 mAh g−1 is achieved with fast Mg2+ diffusion of 7.2 × ${\times }$ 10−11–4 × ${\times }$ 10−14 cm2 s−1. The fast insertion mechanism results from combined cationic redox on the V site and anionic redox on the (S2)2− site; enabled by reversible cleavage of S−S bonds, identified by X‐ray photoelectron and X‐ray absorption spectroscopy. Detailed structural characterisation with maximum entropy method analysis, supported by density functional theory and projected density of states analysis, reveals that the sulphur species involved in anion redox are not connected to the transition metal centres, spatially separating the two redox processes. This facilitates fast and reversible Mg insertion in which the nature of the redox process depends on the cation insertion site, creating a synergy between the occupancy of specific Mg sites and the location of the electrons transferred

Polar Noncentrosymmetric ZnMoSb₂O₇ and Nonpolar Centrosymmetric CdMoSb₄O₁₀: d¹⁰ Transition Metal Size Effect Influencing the Stoichiometry and the Centricity

Two new quaternary molybdenum­(VI) antimony­(III) oxides, ZnMoSb₂O₇ and CdMoSb₄O₁₀, have been synthesized in phase-pure form. The title compounds consist of highly polarizable cations, i.e., d⁰ (Mo⁶⁺) and d¹⁰ (Zn²⁺ or Cd²⁺), and lone-pair cations (Sb³⁺). ZnMoSb₂O₇ exhibits a three-dimensional framework with ZnO₄, MoO₄, and SbO₄ polyhedra in the polar space group <i>P</i>2₁, whereas CdMoSb₄O₁₀ exhibits one-dimensional tubule structures with CdO₆, MoO₄, and SbO₃ polyhedra in the space group <i>P</i>2₁/<i>m</i>. Several synthetic efforts suggest that the the dissimilar radii of Zn²⁺ and Cd²⁺ that can accommodate polyhedra of Sb³⁺ cations influence the stoichiometry as well as the centricity for the reported materials. Spectroscopic, thermal, and elemental analyses are reported along with dipole moment calculations. Nonlinear optical properties and their structural origin are examined for polar ZnMoSb₂O₇ as well

Major Role of Surface Area in Perovskite Electrocatalysts for Alkaline Systems

We investigate the role of lanthanides and the surface area of perovskite oxides to determine the electrocatalytic properties in processes such as the oxygen reduction and evolution reactions. To evaluate the effects of A-site lanthanide and the surface area, a series of lanthanide-based perovskite nanoparticles (LnSCs) were successfully synthesized with simple co-precipitation methods, and electrochemical tests were carried out with the LnSCs. According to the results, the catalytic activities are not affected by the A-site lanthanides, but the surface area was found to be related to the current densities of the perovskite catalysts

Rb2Na(NO3)3: A Congruently Melting UV-NLO Crystal with a Very Strong Second-Harmonic Generation Response

Crystals of congruently melting noncentrosymmetric (NCS) mixed alkali metal nitrate, Rb2Na(NO3)3, have been grown through solid state reactions. The material possesses layers with NaO8 hexagonal bipyramids and NO3 triangular units. Rb+ cations are residing in the interlayer space. Each NaO8 hexagonal bipyramid shares its corners and edges with two and three NO3 units, respectively, in order to fulfill a highly dense stacking in the unit cell. The NaO8 groups share their six oxygen atoms in equatorial positions with three different NO3 groups to generate a NaO6-NO3 layer with a parallel alignment. The optimized arrangement of the NO3 groups and their high density in the structure together produce a strong second-harmonic generation (SHG) response. Powder SHG measurements indicate that Rb2Na(NO3)3 has a strong SHG efficiency of five times that of KH2PO4 (KDP) and is type I phase-matchable. The calculated average nonlinear optical (NLO) susceptibility of Rb2Na(NO3)3 turns out to be the largest value among the NLO materials composed of only [NO3]− anion. In addition, Rb2Na(NO3)3 exhibits a wide transparency region ranging from UV to near IR, which suggests that the compound is a promising NLO material

A Polar Titanium–Organic Chain with a Very Large Second-Harmonic-Generation Response

A noncentrosymmetric (NCS) titanium–organic compound, [H₂N­(CH₃)₂]­TiO­{[NC₅H₃(CO₂)₂]­[NC₅H₄(CO₂)]} (CAUMOF-18), has been synthesized by a solvothermal reaction. The aligned unidimensional polar chain structure of CAUMOF-18 consisting of corner-shared distorted TiO₅N₂ pentagonal bipyramids is attributed to strong hydrogen-bonding and π–π interactions. CAUMOF-18 reveals a very strong second-harmonic-generation efficiency of 400 times that of α-SiO₂ and is phase-matchable (type I). Water-molecule-driven reversible centricity conversion and topotactic transformation to TiO₂ microrods for CAUMOF-18 are also presented

Polymorphisms in <i>M</i>²⁺AlF₅(H₂O)₇ (<i>M</i>^2<i>+</i> = Fe²⁺, Co²⁺, or Ni²⁺): Syntheses, Crystal Structures, and Characterization of New Mixed Metal Fluoride Hydrates

Three new mixed metal fluoride hydrates, M2+AlF5(H2O)7 (M2+ = Fe2+, Co2+, or Ni2+), were synthesized and characterized. The crystals of M2+AlF5(H2O)7 were obtained using a hydrothermal method with a CF3COOH aqueous solution. The crystal structures displayed polymorphisms in C2/m (No. 12) or P-1 (No. 2) space groups, depending on temperature variations. The observed polymorphisms in M2+AlF5(H2O)7 are associated with changes in the bonding environment of [M(H2O)6]2+ and [AlF5(H2O)]2− octahedra, along with changes in hydrogen bonds and unit cell volumes. Infrared spectra and thermogravimetric analyses confirmed the presence of water molecules. The ultraviolet–visible spectra of M2+AlF5(H2O)7 revealed distinctive absorption bands dependent on the [M(H2O)6]2+ complex. This work provides a detailed account of the synthetic procedure, crystal structures, and spectroscopic characterization of M2+AlF5(H2O)7

Influence of Ca-doping in layered perovskite PrBaCo2O5+delta on the phase transition and cathodic performance of a solid oxide fuel cell

Layered perovskite oxides with the formula LnBaCo(2)O(5+delta) (Ln = Pr, Nd, Sm and Gd) have received attention as promising cathode materials for solid oxide fuel cells (SOFCs) because of their high oxygen diffusion and surface exchange coefficients. Recently, many researchers have reported that substituting barium with strontium or calcium can increase the structural stability, electrical conductivity, and catalytic activity of LnBaCo(2)O(5+delta). In this study, we investigated the effect of Ca doping on the structural, electrical, and electrochemical properties of PrBa1-xCaxCo2O5+delta (x = 0, 0.1, 0.2, 0.3 and 0.4). Increasing the amount of Ca dopant changed the structure of PrBa1-xCaxCo2O5+delta from a layered perovskite to a simple perovskite. At x = 0.3, co-existence of the simple and the layered perovskite structure is observed. Electrical conductivity and electro-chemical performance were improved with increasing amount of Ca in the layered perovskite structure and declined with increasing amount of the simple perovskite phase.clos

Variable Asymmetric Chains in Transition Metal Oxyfluorides: Structure–Second-Harmonic-Generation Property Relationships

Four novel transition metal oxyfluorides, [Zn­(pz)₃]­[MoO₂F₄]·0.1H₂O (<b>1</b>), [Zn­(pz)₂F₂]­[Zn­(pz)₃]₂[WO₂F₄]₂ (<b>2</b>), [Cd­(pz)₄]­[Cd­(pz)₄(H₂O)]­[MoO₂F₄]₂·0.625H₂O (<b>3</b>), and [Zn­(mpz)₃]₂[MoO₂F₄]₂ (<b>4</b>) (pz = pyrazole; mpz = 3-methyl pyrazole) have been synthesized. Compounds <b>1</b> and <b>4</b> contain helical chains. Compound <b>2</b> accommodates zigzag chains, and compound <b>3</b> has quasi-one-dimensional linear chains. The variable chain structures are found to be attributable to the different structure-directing anionic groups and hydrogen bonding interactions. Compound <b>4</b> crystallized in the noncentrosymmetric (NCS) polar space group, <i>Pna</i>2₁, is nonphase-matchable (Type I), and reveals a moderate second-harmonic-generation (SHG) efficiency (10 × α-SiO₂). The observed SHG efficiency of compound <b>4</b> is due to the small net polarization occurring from the arrangement of ZnN₃F₂ trigonal bipyramids. Spectroscopic and thermal characterizations along with calculations for the title materials are reported