Manganoan rockbridgeite Fe4.32Mn0.62Zn0.06(PO4)3(OH)5: structure analysis and 57Fe Mössbauer spectroscopy

The structure of the basic iron phosphate rockbridgeite [iron manganese zinc tris­(phosphate) penta­hydroxide] was reinvestigated with special emphasis on the cation distribution deduced from new X‐ray and ⁵⁷Fe Mössbauer data. Rockbridgeite is orthorhombic, space group Cmcm, and shows three different Fe sites, one with symmetry, another with m symmetry and the third in a general position. One phosphate group has the P atom on a site with m symmetry, while the other has the P atom at a site with mm symmetry. Two Fe sites are fully occupied by ferric iron, while Mn³⁺ and Fe²⁺ are situated at a third, principally Fe, site. Structural data, bond‐valence sums and polyhedral distortion parameters suggest a new inter­pretation of the rockbridgeite ⁵⁷Fe Mössbauer spectrum.     

Deep hydration of an Li7–3xLa3Zr2MIIIxO12 solid-state electrolyte material: a case study on Al- and Ga-stabilized LLZO

Single crystals of an Li-stuffed, Al- and Ga-stabilized garnet-type solid-state electrolyte material, Li₇La₃Zr₂O₁₂ (LLZO), have been analysed using single-crystal X-ray diffraction to determine the pristine structural state immediately after synthesis via ceramic sintering techniques. Hydrothermal treatment at 150 °C for 28 d induces a phase transition in the Al-stabilized compound from the commonly observed cubic Iad structure to the acentric I3d subtype. Li^I ions at the interstitial octahedrally (4 + 2-fold) coordinated 48e site are most easily extracted and Al^III ions order onto the tetrahedral 12a site. Deep hydration induces a distinct depletion of Li^I at this site, while the second tetrahedral site, 12b, suffers only minor Li^I loss. Charge balance is maintained by the incorporation of H^I, which is bonded to an O atom. Hydration of Ga-stabilized LLZO induces similar effects, with complete depletion of Li^I at the 48e site. The Li^I/H^I exchange not only leads to a distinct increase in the unit-cell size, but also alters some bonding topology, which is discussed here.     

Commensurate monoclinic form of Ca2Zn0.97Co0.03Ge2O7

Cobalt‐doped dicalcium zinc germanate, synthesized by slow cooling from the melt, is monoclinic and has a layered structure, which is different from the modulated melilite‐type structure of Ca₂ZnGe₂O₇. The monoclinic form has two different Ca, one Zn and two Ge sites, and seven independent O‐atom positions; all are in general position 4e of the space group P2₁/n. The topology of the structure is described and compared with that of Ca₂ZnGe_1.25Si_0.75O₇.     

Substrate-Enabled Room-Temperature Electrochemical Deposition of Crystalline ZnMnO3

Mixed transition metal oxides have emerged as promising electrode materials for electrochemical energy storage and conversion. To optimize the functional electrode properties, synthesis approaches allowing for a systematic tailoring of the materials’ composition, crystal structure and morphology are urgently needed. Here we report on the room-temperature electrodeposition of a ternary oxide based on earth-abundant metals, specifically, the defective cubic spinel ZnMnO₃. In this unprecedented approach, ZnO surfaces act as (i) electron source for the interfacial reduction of MnO₄⁻ in aqueous solution, (ii) as substrate for epitaxial growth of the deposit and (iii) as Zn precursor for the formation of ZnMnO₃. Epitaxial growth of ZnMnO₃ on the lateral facets of ZnO nanowires assures effective electronic communication between the electroactive material and the conducting scaffold and gives rise to a pronounced 2-dimensional morphology of the electrodeposit forming – after partial delamination from the substrate – twisted nanosheets. The synthesis strategy shows promise for the direct growth of different mixed transition metal oxides as electroactive phase onto conductive substrates and thus for the fabrication of binder-free nanocomposite electrodes.     

Ca3ZnGeO2[Ge4O12]: a Ca–Zn germanate related to the mineral taikanite

The title compound, Ca₃ZnGeO₂[Ge₄O₁₂] (tricalcium zinc germanium dioxide dodecaoxidotetragermanate), adopts a taikanite‐type structure. The tetrahedral [Ge₄O₁₂] chain geometry is very similar to that of the silicate chain of taikanite, i.e. BaSr₂Mn³⁺₂O₂[Si₄O₁₂], while the major difference is found parallel to the c axis. In taikanite, Mn³⁺ octahedra form an infinite zigzag chain, whereas the title compound has a chain of distorted ZnO₆ octahedra, which alternates with distorted GeO₄ tetrahedra connected to each other via two common edges. Eightfold‐coordinated Ca²⁺ polyhedra and ZnO₆ octahedra form a slab parallel to (001) which alternates with another slab containing the tetrahedrally coordinated Ge sites along the c axis.     

Solid Electrolytes: Extremely Fast Charge Carriers in Garnet‐Type Li6La3ZrTaO12 Single Crystals

The development of all‐solid‐state electrochemical energy storage systems, such as lithium‐ion batteries with solid electrolytes, requires stable, electronically insulating compounds with exceptionally high ionic conductivities. Considering ceramic oxides, garnet‐type LiLaZrO and derivatives, see Zr‐exchanged LiLaZrTaO (LLZTO), have attracted great attention due to its high Li⁺ ionic conductivity of 10 S cm at ambient temperature. Despite numerous studies focussing on conductivities of powder samples, only few use time‐domain NMR methods to probe Li ion diffusion parameters in single crystals. Here we report on temperature‐variable NMR relaxometry measurements using both laboratory and spin‐lock techniques to probe Li jump rates covering a dynamic time window spanning several decades. Both techniques revealed a consistent picture of correlated Li ion jump diffusion in the single crystal; the data perfectly mirror a modified BPP‐type relaxation response being based on a Lorentzian‐shaped relaxation function. The rates measured could be parameterized with a single set of diffusion parameters. Results from NMR are completely in line with ion transport parameters derived from conductivity spectroscopy.     

β‐Y2Si2O7, a new thortveitite‐type compound,determined at 100 and 280 K

A new form of Y₂Si₂O₇ (diyttrium heptaoxodisilicate) has been synthesized which is isotypic with thortveitite, Sc₂Si₂O₇, and crystallizes in the centrosymmetric space group C2/m, both at 100 and 280 K. The Y³⁺ cation occupies a distorted octahedral site, with Y—O bond lengths in the range 2.239 (2)–2.309 (2) Å. The SiO₄ tetrahedron is remarkably regular, with Si—O bond lengths in the range 1.619 (2)–1.630 (2) Å. The bridging O atom of the Si₂O₇ pyrosilicate group shows a large anisotropic displacement perpendicular to the Si—O bond. Changes in lattice and structural parameters upon cooling are small with, however, a distinct decrease of the anisotropic displacement of the briding O atom. Structure solution and refinement in the non‐centrosymmetric space group C2 are possible but do not yield a significantly different structure model. The Si—O—Si bond angle of the isolated Si₂O₇ groups is 179.2 (1)° at 280 K in C2 and 180° per symmetry in C2/m. The C2/m structure model is favoured.     

LiInSiO4: a new monovalent–trivalent olivine

The structure of the olivine LiInSiO₄ (lithium indium silicate) is isotypic with LiScSiO₄ and MgMgSiO₄ (forsterite). The main differences between the title compound and the divalent–divalent olivines are found for the bond lengths and angles opposite common edges between the tetrahedron and the Li⁺ and In³⁺ ion sites. The tetrahedron shares one common edge with the Li⁺ site and two common edges with the In³⁺ site. The tetrahedron is distinctly distorted, as are the Li⁺ and In³⁺ sites.     

Magnetic ordering and spin structure in Ca-bearing clinopyroxenes CaM(Si, Ge)2O6, M=Fe, Ni, Co, Mn

The compounds CaFeSi₂O₆ (hedenbergite), CaNiGe₂O₆, CaCoGe₂O₆ and CaMnGe₂O₆ have been synthesized by hydrothermal or ceramic sintering techniques and were subsequently characterized by SQUID magnetometry and powder neutron diffraction in order to determine the magnetic properties and the spin structure at low temperature. All four compounds reveal the well-known clinopyroxene structure-type with monoclinic symmetry, space group C2/c, Z=4 at all temperatures investigated. Below 35 K hedenbergite shows a ferromagnetic (FM) coupling of spins within the infinite M1 chains of edge-sharing octahedra. This FM coupling dominates an antiferromagnetic (AFM) coupling between neighbouring chains. The magnetic moments lie within the a-c plane and form an angle of 43° with the crystallographic a-axis. Magnetic ordering in CaFeSi₂O₆ causes significant discontinuities in lattice parameters, Fe-O bond lengths and interatomic Fe-Fe distances through the magnetic phase transition, which could be detected from the Rietveld refinements of powder neutron diffraction data. CaCoGe₂O₆ and CaNiGe₂O₆ show magnetic ordering below 18 K, the spin structures are similar to the one in hedenbergite with an FM coupling within and an AFM coupling of spins between the M1 chains. The moments lie within the a-c plane. The paramagnetic Curie temperature, however, decreases from CaFeSi₂O₆ (+40.2 K) to CaCoGe₂O₆ (+20.1 K) and CaNiGe₂O₆ (−13.4 K), suggesting an altered interplay between the concurring AFM and FM interaction in and between the M1 chains. CaMnGe₂O₆ finally shows an AFM ordering below 11 K. Here the magnetic moments are mainly oriented along the a-axis with a small tilt out from the a-c plane.     

The ferriannite KFe(Al0.26FeSi3)­O10(OH)2 at 100 and 270 K

Unusually large and good‐quality single crystals of the synthetic trioctahedral mica KFe(Al_0.26FeSi₃)O₁₀(OH)₂ [potassium triiron(II) aluminasilaferrate(III) decaoxide dihy­droxide] have been grown hydro­thermally. X‐ray diffraction data measured at 270 and 100 K have been used to refine the crystal structure, including the positions of the H atoms. This synthetic mica is similar to annite, KFe₃AlSi₃O₁₀(OH)₂, and crystallizes with the same monoclinic C2/m symmetry. No phase transition has been observed down to 100 K. At low temperature, the ditrigonal distortion of the mica structure increases markedly, while the octahedral and tetrahedral bond lengths tend to decrease and increase, respectively. A detailed comparison of structural parameters in various Fe‐rich micas is presented.