Synthesis, Structural Characterization, and Lithium Ion Conductivity of the Lithium Thiophosphate Li2P2S6.

Inspired by the ongoing search for new superionic lithium thiophosphates for use in solid-state batteries, we present the synthesis and structural characterization of Li2P2S6, a novel crystalline lithium thiophosphate. Whereas M2P2S6 with the different alkaline elements (M = Na, K, Rb, Cs) is known, the lithium counterpart has not been reported yet. Herein, we present a combination of synchrotron pair distribution function analysis and neutron powder diffraction to elucidate the crystal structure and possible Li+ diffusion pathways of Li2P2S6. Additionally, impedance spectroscopy is used to evaluate its ionic conductivity. We show that Li2P2S6 possesses P2S62- polyhedral units with edge-sharing PS4 tetrahedra and only one-dimensional diffusion pathways with localized Li-Li pairs, leading to a low ionic conductivity for lithium.

Soft chemical control of superconductivity in lithium iron selenide hydroxides Li(1-x)Fe(x)(OH)Fe(1-y)Se.

Hydrothermal synthesis is described of layered lithium iron selenide hydroxides Li(1-x)Fe(x)(OH)Fe(1-y)Se (x ∼ 0.2; 0.02 < y < 0.15) with a wide range of iron site vacancy concentrations in the iron selenide layers. This iron vacancy concentration is revealed as the only significant compositional variable and as the key parameter controlling the crystal structure and the electronic properties. Single crystal X-ray diffraction, neutron powder diffraction, and X-ray absorption spectroscopy measurements are used to demonstrate that superconductivity at temperatures as high as 40 K is observed in the hydrothermally synthesized samples when the iron vacancy concentration is low (y < 0.05) and when the iron oxidation state is reduced slightly below +2, while samples with a higher vacancy concentration and a correspondingly higher iron oxidation state are not superconducting. The importance of combining a low iron oxidation state with a low vacancy concentration in the iron selenide layers is emphasized by the demonstration that reductive postsynthetic lithiation of the samples turns on superconductivity with critical temperatures exceeding 40 K by displacing iron atoms from the Li(1-x)Fe(x)(OH) reservoir layer to fill vacancies in the selenide layer.

Ammonia-rich high-temperature superconducting intercalates of iron selenide revealed through time-resolved in situ X-ray and neutron diffraction.

The development of a technique for following in situ the reactions of solids with alkali metal/ammonia solutions, using time-resolved X-ray diffraction methods, reveals high-temperature superconducting ammonia-rich intercalates of iron selenide which reversibly absorb and desorb ammonia around ambient temperatures.

Enhancement of the superconducting transition temperature of FeSe by intercalation of a molecular spacer layer.

The discovery of high-temperature superconductivity in a layered iron arsenide has led to an intensive search to optimize the superconducting properties of iron-based superconductors by changing the chemical composition of the spacer layer between adjacent anionic iron arsenide layers. Superconductivity has been found in iron arsenides with cationic spacer layers consisting of metal ions (for example, Li(+), Na(+), K(+), Ba(2+)) or PbO- or perovskite-type oxide layers, and also in Fe(1.01)Se (ref. 8) with neutral layers similar in structure to those found in the iron arsenides and no spacer layer. Here we demonstrate the synthesis of Li(x)(NH(2))(y)(NH(3))(1-y)Fe(2)Se(2) (x~0.6; y~0.2), with lithium ions, lithium amide and ammonia acting as the spacer layer between FeSe layers, which exhibits superconductivity at 43(1) K, higher than in any FeSe-derived compound reported so far. We have determined the crystal structure using neutron powder diffraction and used magnetometry and muon-spin rotation data to determine the superconducting properties. This new synthetic route opens up the possibility of further exploitation of related molecular intercalations in this and other systems to greatly optimize the superconducting properties in this family.

Metal-organic framework luminescence in the yellow gap by codoping of the homoleptic imidazolate ∞(3)[Ba(Im)2] with divalent europium.

The rare case of a metal-triggered broad-band yellow emitter among inorganic-organic hybrid materials was achieved by in situ codoping of the novel imidazolate metal-organic framework ∞(3)[Ba(Im)2] with divalent europium. The emission maximum of this dense framework is in the center of the yellow gap of primary light-emitting diode phosphors. Up to 20% Eu2+ can be added to replace Ba2+ as connectivity centers without causing observable phase segregation. High-resolution energy-dispersive X-ray spectroscopy showed that incorporation of even 30% Eu2+ is possible on an atomic level, with 2-10% Eu2+ giving the peak quantum efficiency (QE = 0.32). The yellow emission can be triggered by two processes: direct excitation of Eu2+ and an antenna effect of the imidazolate linkers. The emission is fully europium-centered, involving 5d → 4f transitions, and depends on the imidazolate surroundings of the metal ions. The framework can be obtained by a solvent-free in situ approach starting from barium metal, europium metal, and a melt of imidazole in a redox reaction. Better homogeneity for the distribution of the luminescence centers was achieved by utilizing the hydrides BaH2 and EuH2 instead of the metals.

High-pressure synthesis and structural investigation of H3P8O8N9: a new phosphorus(V) oxonitride imide with an interrupted framework structure.

The first crystalline phosphorus oxonitride imide H(3)P(8)O(8)N(9) (=P(8)O(8)N(6)(NH)(3)) has been synthesized under high-pressure and high-temperature conditions. To this end, a new, highly reactive phosphorus oxonitride imide precursor compound was prepared and treated at 12 GPa and 750 °C by using a multianvil assembly. H(3)P(8)O(8)N(9) was obtained as a colorless, microcrystalline solid. The crystal structure of H(3)P(8)O(8)N(9) was solved ab initio by powder X-ray diffraction analysis, applying the charge-flipping algorithm, and refined by the Rietveld method (C2/c (no. 15), a=1352.11(7), b=479.83(3), c=1820.42(9) pm, ß=96.955(4)°, Z=4). H(3)P(8)O(8)N(9) exhibits a highly condensed (κ=0.47), 3D, but interrupted network that is composed of all-side vertex-sharing (Q(4)) and only threefold-linking (Q(3)) P(O,N)(4) tetrahedra in a Q(4)/Q(3) ratio of 3:1. The structure, which includes 4-ring assemblies as the smallest ring size, can be subdivided into alternating open-branched zweier double layers {oB,2(2)(∞)}[(2)P(3)(O,N)(7)] and layers containing pairwise-linked Q(3) tetrahedra parallel (001). Information on the hydrogen atoms in H(3)P(8)O(8)N(9) was obtained by 1D (1)H MAS, 2D homo- and heteronuclear (together with (31)P) correlation NMR spectroscopy, and a (1)H spin-diffusion experiment with a hard-pulse sequence designed for selective excitation of a single peak. Two hydrogen sites with a multiplicity ratio of 2:1 were identified and thus the formula of H(3)P(8)O(8)N(9) was unambiguously determined. The protons were assigned to Wyckoff positions 8f and 4e, the latter located within the Q(3) tetrahedra layers.

Unprecedented zeolite-like framework topology constructed from cages with 3-rings in a barium oxonitridophosphate.

A novel oxonitridophosphate, Ba(19)P(36)O(6+x)N(66-x)Cl(8+x) (x ≈ 4.54), has been synthesized by heating a multicomponent reactant mixture consisting of phosphoryl triamide OP(NH(2))(3), thiophosphoryl triamide SP(NH(2))(3), BaS, and NH(4)Cl enclosed in an evacuated and sealed silica glass ampule up to 750 °C. Despite the presence of side phases, the crystal structure was elucidated ab initio from high-resolution synchrotron powder diffraction data (λ = 39.998 pm) applying the charge flipping algorithm supported by independent symmetry information derived from electron diffraction (ED) and scanning transmission electron microscopy (STEM). The compound crystallizes in the cubic space group Fm ̅3c (no. 226) with a = 2685.41(3) pm and Z = 8. As confirmed by Rietveld refinement, the structure comprises all-side vertex sharing P(O,N)(4) tetrahedra forming slightly distorted 3(8)4(6)8(12) cages representing a novel composite building unit (CBU). Interlinked through their 4-rings and additional 3-rings, the cages build up a 3D network with a framework density FD = 14.87 T/1000 Å(3) and a 3D 8-ring channel system. Ba(2+) and Cl(-) as extra-framework ions are located within the cages and channels of the framework. The structural model is corroborated by (31)P double-quantum (DQ) /single-quantum (SQ) and triple-quantum (TQ) /single-quantum (SQ) 2D correlation MAS NMR spectroscopy. According to (31)P{(1)H} C-REDOR NMR measurements, the H content is less than one H atom per unit cell.

SrP3N5O: a highly condensed layer phosphate structure solved from a nanocrystal by automated electron diffraction tomography.

The oxonitridophosphate SrP(3)N(5)O has been synthesized by heating a multicomponent reactant mixture that consisted of phosphoryl triamide OP(NH(2))(3), thiophosphoryl triamide SP(NH(2))(3), SrS, and NH(4)Cl enclosed in evacuated and sealed silica-glass ampoules up to 750 °C. The compound was obtained as nanocrystalline powder with needle-shaped crystallites. The crystal structure was solved ab initio on the basis of electron diffraction data by means of automated electron diffraction tomography (ADT) and verified by Rietveld refinement with X-ray powder diffraction data. SrP(3)N(5)O crystallizes in the orthorhombic space group Pnma (no. 62) with unit-cell data of a=18.331(2), b=8.086(1), c=13.851(1) Å and Z=16. The compound is a highly condensed layer phosphate with a degree of condensation κ=½. The corrugated layers (∞)(2){(P(3)N(5)O)(2-)} consist of linked, triangular columns built up from P(O,N)(4) tetrahedra with 3-rings and triply binding nitrogen atoms. The Sr(2+) ions are located between the layers and exhibit six-, eight-, and ninefold coordination. FTIR and solid-state NMR spectra of SrP(3)N(5)O are discussed as well.

Artificial Solid Electrolyte Interphases for Lithium Metal Electrodes by Wet Processing: The Role of Metal Salt Concentration and Solvent Choice.

In this study, the artificial solid electrolyte interphase (SEI) formed on lithium metal when treated in ZnCl2 solutions is thoroughly investigated. The artificial SEI on lithium metal electrodes substantially decreases the interfacial resistance by ca. 80% and improves cycling stability in comparison to untreated lithium. The presence of a native SEI negatively affects the morphology and interfacial resistance of the artificial SEI. Increasing the ZnCl2 concentration in tetrahydrofuran (THF) (precursor solution) results in higher homogeneity of the surface morphology. Independent of the ZnCl2 concentrations, the artificial SEI is composed of Cx, CO, LiCl, Li2CO3, ZnCl2, and LixZny alloys. ZnCl2 (1 M) produces the most homogenous surface and additional surface species with carbonyl side groups. Nonetheless, the ZnCl2 concentration only has a small effect on the interfacial resistance or cycling stability. Using ethyl methyl carbonate (EMC) as the solvent significantly reduces the interfacial resistance to 7 Ω cm2, in comparison to 25 Ω cm2 for THF. The composition of the artificial SEIs varies depending on the solvent. Either way, the SEI consists of Cx LixC, LiCl, Li2CO3, ZnCl2, and LiZn alloys. The THF-based SEI additionally features ether and carbonyl groups, LiZnO, and Zn metal. For the artificial SEI formed with both solvents, the atomic percentage of the LiZn alloy increases close to the Li surface.

High-Throughput Screening of Solid-State Li-Ion Conductors Using Lattice-Dynamics Descriptors.

Low lithium-ion migration barriers have recently been associated with low average vibrational frequencies or phonon band centers, further helping identify descriptors for superionic conduction. To further explore this correlation, here we present the computational screening of ∼14,000 Li-containing compounds in the Materials Project database using a descriptor based on lattice dynamics reported recently to identify new promising Li-ion conductors. An efficient computational approach was optimized to compute the average vibrational frequency or phonon band center of ∼1,200 compounds obtained after pre-screening based on structural stability, band gap, and their composition. Combining a low computed Li phonon band center with large computed electrochemical stability window and structural stability, 18 compounds were predicted to be promising Li-ion conductors, one of which, Li3ErCl6, has been synthesized and exhibits a reasonably high room-temperature conductivity of 0.05-0.3 mS/cm, which shows the promise of Li-ion conductor discovery based on lattice dynamics.

Insight in the 3D morphology of silica-based nanotubes using electron microscopy.

Amorphous silica-based nanotubes (SBNTs) were synthesized from phosphoryl triamide, OP(NH2)3, thiophosphoryl triamide, SP(NH2)3, and silicon tetrachloride, SiCl4, at different temperatures and with varying amount of the starting material SiCl4 using a recently developed template-free synthesis approach. Diameter and length of the SBNTs are tunable by varying the synthesis parameters. The 3D mesocrystals of the SBNTs were analyzed with focused ion beam sectioning and electron tomography in the transmission electron microscope showing the hollow tubular structure of the SBNTs. The reconstruction of a small SBNT assembly was achieved from a high-angle annular-dark field scanning transmission electron microscopy tilt series containing only thirteen images allowing analyzing beam sensitive material without altering the structure. The reconstruction revealed that the individual nanotubes are forming an interconnected array with an open channel structure.

Sr3P6O6N8--a highly condensed layered phosphate.

We describe the synthesis and the structure elucidation of Sr(3)P(6)O(6)N(8), a novel, highly condensed layered phosphate.

Crystal structures of incommensurately modulated Ln(PO3)3 (Ln=Tb-Yb) and commensurate Gd(PO3)3 and Lu(PO3)3.

The crystal structure of the late lanthanoids' catena-polyphosphates Ln(PO3)3 (Ln=Tb-Yb) is incommensurately modulated (Dy(PO3)3: space group Cc(0beta0)0; Z=4; a=1417.4(4), b=670.96(14), c=1009.5(3) pm; beta=127.62(2) degrees, q=0.364b*; Rall=0.057, wRall=0.071; 293 K) and consists of infinite chains of corner-sharing PO4 tetrahedra. The cations are coordinated 6-fold in an almost octahedral arrangement over the whole modulation period. All atoms comprise a sinoidal positional modulation. The basic structure can be derived from a fcc packing which explains the pseudo-face-centering observed in the diffraction patterns. The crystal structure of Lu(PO3)3 is isotypic with C-type phosphates (Cc; Z=12; a=1397.2(1), b=2001.8(2), c=995.56(9) pm; beta=127.351(6) degrees; R1=0.042, wR2=0.097, 293 K), and Gd(PO3)3 crystallizes in a new structure type (I2/a; Z=16; a=2601.7(2), b=1351.1(1), c=1008.4(1) pm; beta=119.311(6) degrees; R1=0.039, wR2=0.092; 293 K). Both can be described in terms of superstructures of the basic structure unit cell of the incommensurate phases, and thus, a consistent structural description of many polyphosphates is provided. Tb(PO3)3 was obtained as single phase adopting a novel synthesis under reducing conditions. The absence of an inversion center in the incommensurate phases and Lu(PO3)3 was proved by a SHG experiment. The vibrational spectra are also discussed.