Mo⁶⁺ Cation Enrichment of the Structure Chemistry of Iodates: Syntheses, Structures, and Calculations of Ba(MoO₂)₂(IO₃)₄O, Ba₃[(MoO₂)₂(IO₃)₄O(OH)₄]·2H₂O, and Sr[(MoO₂)₆(IO₄)₂O₄]·H₂O

The three metal iodates Ba­(MoO₂)₂(IO₃)₄O (<b>1</b>), Ba₃[(MoO₂)₂(IO₃)₄O­(OH)₄]·2H₂O (<b>2</b>), and Sr­[(MoO₂)₆(IO₄)₂O₄]·H₂O (<b>3</b>) have been successfully synthesized by introducing second-order Jahn–Teller distorted Mo⁶⁺ cations by a mild hydrothermal method. Single-crystal X-ray diffraction (XRD) was used to determine the structures of the three title compounds. In compound <b>1</b>, the [Mo₂O₁₁]^10– dimers connect with the [IO₃]⁻ units by sharing oxygen atoms to form two-dimensional (2D) layers that are separated by the Ba²⁺ cations. For comparison, the [Mo₂O₁₁]^10– dimers and the [IO₃]⁻ units are isolated in compound <b>2</b>, and they are connected by the [BaO₁₁]^20– polyhedra forming a 3D network. For compound <b>3</b>, the [MoO₆]^6– polyhedra link with each other by corner and edge sharing to build 2D corrugated layers with tunnels containing isolated [IO₄]^3– units. The [SrO₉]^16‑ polyhedra link the 2D corrugated layers to form a 3D network. The infrared (IR) spectra, the ultraviolet–visible–near-infrared (UV–vis–NIR) diffuse reflectance spectra, and thermal stabilities of compounds <b>1</b> and <b>2</b> are presented. In addition, the theoretical calculations are also carried out to evaluate their band gaps and density of states

Expanding Frontiers of Ultraviolet Nonlinear Optical Materials with Fluorophosphates

If a bucket is to hold more water, its shortest plank must be made longer. This guideline also applies to the exploration of ultraviolet (UV) and deep-UV (DUV) nonlinear optical (NLO) materials that are limited by multiple criteria. Phosphates are one kind of promising candidate for new NLO materials. Unfortunately, the small birefringence, as the shortest plank, severely restricts the phase-matching of second harmonic generation (SHG) in the UV/DUV region. In this work, fluorophosphates are rationally proposed as substitutes for phosphates to break down the limitation of birefringence and simultaneously enhance SHG response and retain wide UV transmittance. The (PO₃F)^2– and (PO₂F₂)⁻ groups are confirmed as superior material genomes to achieve the discussed combination properties. Accordingly, (NH₄)₂PO₃F was screened out by density functional theory calculation, and single crystals with centimeter size have been grown. It possesses a powder SHG efficiency of 1 × KH₂PO₄ (KDP) and is phase-matchable with output of SHG wavelength at 266 nm. To the best of our knowledge, it is the first time that fluorophosphates are identified and developed as new and ideal candidates to new UV/DUV NLO materials by combining theories and experiments

Expanding Frontiers of Ultraviolet Nonlinear Optical Materials with Fluorophosphates

If a bucket is to hold more water, its shortest plank must be made longer. This guideline also applies to the exploration of ultraviolet (UV) and deep-UV (DUV) nonlinear optical (NLO) materials that are limited by multiple criteria. Phosphates are one kind of promising candidate for new NLO materials. Unfortunately, the small birefringence, as the shortest plank, severely restricts the phase-matching of second harmonic generation (SHG) in the UV/DUV region. In this work, fluorophosphates are rationally proposed as substitutes for phosphates to break down the limitation of birefringence and simultaneously enhance SHG response and retain wide UV transmittance. The (PO₃F)^2– and (PO₂F₂)⁻ groups are confirmed as superior material genomes to achieve the discussed combination properties. Accordingly, (NH₄)₂PO₃F was screened out by density functional theory calculation, and single crystals with centimeter size have been grown. It possesses a powder SHG efficiency of 1 × KH₂PO₄ (KDP) and is phase-matchable with output of SHG wavelength at 266 nm. To the best of our knowledge, it is the first time that fluorophosphates are identified and developed as new and ideal candidates to new UV/DUV NLO materials by combining theories and experiments

Control of Ionic Conductivity by Lithium Distribution in Cubic Oxide Argyrodites Li_6+<i>x</i>P_1–<i>x</i>Si_<i>x</i>O₅Cl

Argyrodite is a key structure type for ion-transporting materials. Oxide argyrodites are largely unexplored despite sulfide argyrodites being a leading family of solid-state lithium-ion conductors, in which the control of lithium distribution over a wide range of available sites strongly influences the conductivity. We present a new cubic Li-rich (>6 Li+ per formula unit) oxide argyrodite Li7SiO5Cl that crystallizes with an ordered cubic (P213) structure at room temperature, undergoing a transition at 473 K to a Li+ site disordered F4̅3m structure, consistent with the symmetry adopted by superionic sulfide argyrodites. Four different Li+ sites are occupied in Li7SiO5Cl (T5, T5a, T3, and T4), the combination of which is previously unreported for Li-containing argyrodites. The disordered F4̅3m structure is stabilized to room temperature via substitution of Si4+ with P5+ in Li6+xP1–xSixO5Cl (0.3 x < 0.85) solid solution. The resulting delocalization of Li+ sites leads to a maximum ionic conductivity of 1.82(1) × 10–6 S cm–1 at x = 0.75, which is 3 orders of magnitude higher than the conductivities reported previously for oxide argyrodites. The variation of ionic conductivity with composition in Li6+xP1–xSixO5Cl is directly connected to structural changes occurring within the Li+ sublattice. These materials present superior atmospheric stability over analogous sulfide argyrodites and are stable against Li metal. The ability to control the ionic conductivity through structure and composition emphasizes the advances that can be made with further research in the open field of oxide argyrodites