Rutile-type compounds. IV. SiO2, GeO2 and a comparison with other rutile-type structures

Highly Reversible Conversion-Type CoSn2 Cathode for Fluoride-Ion Batteries

An all-solid-state fluoride-ion battery (FIB) is one of the promising candidates for the next-generation battery owing to its high energy density and high safety. For the practical application of FIBs, it is an urgent task to operate FIBs at lower temperatures. However, there are still two major difficulties in conventional conversion-type pure metal cathodes: low F- ion conductivities and poor cycle stabilities. Here, the conversion-type Sn-based intermetallic alloy is proposed as a new cathode that can overcome the above issues. The present CoSn2 cathode retains the discharge capacity of 229 mAh g-1 after 250 cycles, even at 60 °C. CoSn2 is decomposed into CoF2 and SnF2 nanocrystals in the charging process, and the nanoscale network structure of SnF2 provides the fast F- ion conduction path throughout the cathode, facilitating the battery operation at lower temperatures. Moreover, the formed CoF2 and SnF2 phases are merged into the original CoSn2 phase in the discharging process, leading to a highly reversible redox reaction and the high cycle stability of CoSn2. These findings should pave the way to enhance the performance of all-solid-state FIBs at lower temperatures.

Investigating the Local Bonding Structure of Amorphous Zinc Tin Oxide to Elucidate the Effect of Altering the Intercation Ratio

In this paper, the local bonding structure in amorphous zinc tin oxide (a-ZTO) is probed using a combination of XANES and EXAFS techniques at the Zn and Sn K-edges to gain insight into charge carrier generation in the material. a-ZTO is prepared using two growth methods; spray pyrolysis and magnetron sputtering. It is seen that a-ZTO grown by magnetron sputtering shows no changes in the chemical environment as the cation ratio is varied; meanwhile, XANES analysis of spray pyrolysis grown samples shows alterations to spectra likely due to the effects caused by different precursors. Although a slight shift in Sn-O bond length is visible between magnetron sputtered and spray grown samples, no correlation could be discerned between bond length and variation in cation ratio. It is concluded that a-ZTO, while amorphous over longer ranges, is locally composed of ZnO and SnO2 "building blocks". An alteration in the cation ratio changes the hybridization at the conduction band minimum, resulting in the observed variation in the mobility, charge carrier concentration, and bandgap.

Impact of Nickel on Iridium-Ruthenium Structure and Activity for the Oxygen Evolution Reaction under Acidic Conditions

Proton exchange membrane water electrolysis (PEMWE) is a promising technology to produce hydrogen directly from renewable electricity sources due to its high power density and potential for dynamic operation. Widespread application of PEMWE is, however, currently limited due to high cost and low efficiency, for which high loading of expensive iridium catalyst and high OER overpotential, respectively, are important reasons. In this study, we synthesize highly dispersed IrRu nanoparticles (NPs) supported on antimony-doped tin oxide (ATO) to maximize catalyst utilization. Furthermore, we study the effect of adding various amounts of Ni to the synthesis, both in terms of catalyst structure and OER activity. Through characterization using various X-ray techniques, we determine that the presence of Ni during synthesis yields significant changes in the structure of the IrRu NPs. With no Ni present, metallic IrRu NPs were synthesized with Ir-like structure, while the presence of Ni leads to the formation of IrRu oxide particles with rutile/hollandite structure. There are also clear indications that the presence of Ni yields smaller particles, which can result in better catalyst dispersion. The effect of these differences on OER activity was also studied through rotating disc electrode measurements. The IrRu-supported catalyst synthesized with Ni exhibited OER activity of up to 360 mA mgPGM -1 at 1.5 V vs RHE. This is ∼7 times higher OER activity than the best-performing IrO x benchmark reported in the literature and more than twice the activity of IrRu-supported catalyst synthesized without Ni. Finally, density functional theory (DFT) calculations were performed to further elucidate the origin of the observed activity enhancement, showing no improvement in intrinsic OER activity for hollandite Ir and Ru compared to the rutile structures. We, therefore, hypothesize that the increased activity measured for the IrRu supported catalyst synthesized with Ni present is instead due to increased electrochemical surface area.

How the Interplay between SnO2 and Zn(II) Porphyrins Impacts on the Electronic Features of Gaseous Acetone Chemiresistors

Herein, the integration of SnO2 nanoparticles with two Zn(II) porphyrins─Zn(II) 5,10,15,20-tetraphenylporphyrin (ZnTPP) and its perfluorinated counterpart, Zn(II) 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (ZnTPPF20)─was investigated for the sensing of gaseous acetone at 120 °C, adopting three Zn-porphyrin/SnO2 weight ratios (1:4, 1:32, and 1:64). For the first time, we were able to provide evidence of the correlation between the materials' conductivity and these nanocomposites' sensing performances, obtaining optimal results with a 1:32 ratio for ZnTPPF20/SnO2 and showcasing a remarkable detection limit of 200 ppb together with a boosted sensing signal with respect to bare SnO2. To delve deeper, the combination of experimental data with density functional theory calculations unveiled an electron-donating behavior of both porphyrins when interacting with tin dioxide semiconductor, especially for the nonfluorinated one. The study suggested that the interplay between electrons injected, from the porphyrins' highest occupied molecular orbital to SnO2 conduction band, and the latter's available electronic states has a dramatic impact to boost the chemiresistive sensing. Indeed, we highlighted that the key lies in preventing the full saturation of SnO2 electronic states concomitantly increasing the materials' conductivity: in this respect, the best compromise turned out to be the perfluorinated porphyrin. A further corroboration of our findings was obtained by illuminating the sensors during measurements with light-emitting diode (LED) light. Actually, we demonstrated that it does not have any impact on improving the sensing behavior, most probably due to the electronic oversaturation and scattering caused by LED excitation in porphyrins. Lastly, the most effective hybrids (1:32 ratio) were physicochemically characterized, confirming the physisorption of the macrocycles onto the SnO2 surface. In conclusion, herein, we underscore the feasibility of customizing the porphyrin chemistry and porphyrin-to-SnO2 ratio to enhance the gaseous sensing of bare metal oxides, providing valuable insights for the engineering of highly performing light-free chemiresistors.

Designing and synthesis of perovskite nanocrystals: a promising wide-spectrum solar light-responsive photocatalyst and lead ion sensor

Perovskites are an emerging material with a variety of applications, ranging from their solar light conversion capability to their sensing efficiency. In current study, perovskite nanocrystals (PNCs) were designed using theoretical density functional theory (DFT) analysis. Moreover, the theoretically designed PNCs were fabricated and confirmed by various characterization techniques. The calculated optical bandgap from UV-Vis and fluorescence spectra were 2.15 and 2.05 eV, respectively. The average crystallite size of PNCs calculated from Scherrer equation was 15.18 nm, and point of zero charge (PZC) was obtained at pH 8. The maximum eosin B (EB) removal efficiency by PNCs was 99.56% at optimized conditions following first-order kinetics with 0.98 R2 value. The goodness of the response surface methodology (RSM) model was confirmed from analysis of variance (ANOVA), with the experimental F value (named after Ronald Fisher) of 194.66 being greater than the critical F value F0.05, 14, 14 = 2.48 and a lack of fit value of 0.0587. The Stern-Volmer equation with a larger Ksv value of 1.303710 × 10 6 for Pb2+ suggests its greater sensitivity for Pb2+ among the different metals tested.

An Unexpected Decrease in Vibrational Entropy of Multicomponent Rutile Oxides

High-entropy oxides (HEOs), featuring infinite chemical composition and exceptional physicochemical properties, are attracting much attention. The configurational entropy caused by a component disorder of HEOs is popularly believed to be the main driving force for thermal stability, while the role of vibrational entropy in the thermodynamic landscape has been neglected. In this study, we systematically investigated the vibrational entropy of multicomponent rutile oxides (including Fe0.5Ta0.5O2, Fe0.333Ti0.333Ta0.333O2, Fe0.25Ti0.25Ta0.25Sn0.25O2, and Fe0.21Ti0.21Ta0.21Sn0.21Ge0.16O2) by precise heat capacity measurements. It is found that vibrational entropy gradually decreases with increasing component disorder, beyond what one could expect from an equilibrium thermodynamics perspective. Moreover, all multicomponent rutile oxides exhibit a positive excess vibrational entropy at 298.15 K. Upon examinations of configuration disorder, size mismatch, phase transition, and polyhedral distortions, we demonstrate that the excess vibrational entropy plays a pivotal role in lowering the crystallization temperature of multicomponent rutile oxides. These findings represent the first experimental confirmation of the role of lattice vibrations in the thermodynamic landscape of rutile HEOs. In particular, vibrational entropy could serve as a novel descriptor to guide the predictive design of multicomponent oxide materials.

Subnanometric Osmium Clusters Confined on Palladium Metallenes for Enhanced Hydrogen Evolution and Oxygen Reduction Catalysis

Highly efficient, cost-effective, and durable electrocatalysts, capable of accelerating sluggish reaction kinetics and attaining high performance, are essential for developing sustainable energy technologies but remain a great challenge. Here, we leverage a facile heterostructure design strategy to construct atomically thin Os@Pd metallenes, with atomic-scale Os nanoclusters of varying geometries confined on the surface layer of the Pd lattice, which exhibit excellent bifunctional properties for catalyzing both hydrogen evolution (HER) and oxygen reduction reactions (ORR). Importantly, Os5%@Pd metallenes manifest a low η10 overpotential of only 11 mV in 1.0 M KOH electrolyte (HER) as well as a highly positive E1/2 potential of 0.92 V in 0.1 M KOH (ORR), along with superior mass activities and electrochemical durability. Theoretical investigations reveal that the strong electron redistribution between Os and Pd elements renders a precise fine-tuning of respective d-band centers, thereby guiding adsorption of hydrogen and oxygen intermediates with an appropriate binding energy for the optimal HER and ORR.

Polymorphism and Structural Variety in Sn(II) Carboxylate Coordination Polymers Revealed from Structure Solution of Microcrystals

The crystal structures of four coordination polymers constructed from Sn(II) and polydentate carboxylate ligands are reported. All are prepared under hydrothermal conditions in KOH or LiOH solutions (either water or methanol-water) at 130-180 °C and crystallize as small crystals, microns or less in size. Single-crystal structure solution and refinement are performed using synchrotron X-ray diffraction for two materials and using 3D electron diffraction (3DED) for the others. Sn2 (1,3,5-BTC)(OH), where 1,3,5-BTC is benzene-1,3,5-tricarboxylate, is a new polymorph of this composition and has a three-dimensionally connected structure with potential for porosity. Sn(H-1,3,5-BTC) retains a partially protonated ligand and has a 1D chain structure bound by hydrogen bonding via ─COOH groups. Sn(H-1,2,4-BTC) contains an isomeric ligand, benzene-1,2,4-tricarboxylate, and contains inorganic chains in a layered structure held by hydrogen bonding. Sn2 (DOBDC), where DOBDC is 2,5-dioxido-benzene-1,4-dicarboxylate, is a new polymorph for this composition and has a three-dimensionally connected structure where both carboxylate and oxido groups bind to the tin centers to create a dense network with dimers of tin. In all materials, the Sn centers are found in highly asymmetric coordination, as expected for Sn(II). For all materials phase purity of the bulk is confirmed using powder X-ray diffraction, thermogravimetric analysis, and infrared spectroscopy.

Locality error free effective core potentials for 3d transition metal elements developed for the diffusion Monte Carlo method

Pseudopotential locality errors have hampered the applications of the diffusion Monte Carlo (DMC) method in materials containing transition metals, in particular oxides. We have developed locality error free effective core potentials, pseudo-Hamiltonians, for transition metals ranging from Cr to Zn. We have modified a procedure published by some of us in Bennett et al. [J. Chem. Theory Comput. 18, 828 (2022)]. We carefully optimized our pseudo-Hamiltonians and achieved transferability errors comparable to the best semilocal pseudopotentials used with DMC but without incurring in locality errors. Our pseudo-Hamiltonian set (named OPH23) bears the potential to significantly improve the accuracy of many-body-first-principles calculations in fundamental science research of complex materials involving transition metals.

Unexpected Coexisting Solid Solutions in the Quasi-Binary Ag(II) F2 /Cu(II) F2 Phase Diagram

High-temperature solid-state reaction between orthorhombic AgF2 and monoclinic CuF2 (y=0.15, 0.3, 0.4, 0.5) in a fluorine atmosphere resulted in coexisting solid solutions of Cu-poor orthorhombic and Cu-rich monoclinic phases with stoichiometry Ag1-x Cux F2 . Based on X-ray powder diffraction analyses, the mutual solubility in the orthorhombic phase (AgF2  : Cu) appears to be at an upper limit of Cu concentration of 30 mol % (Ag0.7 Cu0.3 F2 ), while the monoclinic phase (CuF2  : Ag) can form a nearly stoichiometric Cu : Ag=1 : 1 solid solution (Cu0.56 Ag0.44 F2 ), preserving the CuF2 crystal structure. Experimental data and DFT calculations showed that AgF2  : Cu and CuF2  : Ag solid solutions deviate from the classical Vegard's law. Magnetic measurements of Ag1-x Cux F2 showed that the Néel temperature (TN ) decreases with increasing Cu content in both phases. Likewise, theoretical DFT+U calculations for Ag1-x Cux F2 showed that the progressive substitution of Ag by Cu decreases the magnetic interaction strength |J2D | in both structures. Electrical conductivity measurements of Ag0.85 Cu0.15 F2 showed a modest increase in specific ionic conductivity (3.71 ⋅ 10-13 ±2.6 ⋅ 10-15  S/cm) as compared to pure AgF2 (1.85 ⋅ 10-13± 1.2 ⋅ 10-15  S/cm), indicating the formation of a vacancy- or F adatom-free metal difluoride sample.

Investigation of Charge-Ordered Barium Iron Fluorides with One-Dimensional Structural Diversity and Complex Magnetic Interactions

Three mixed-valence barium iron fluorides, Ba7Fe7F34, Ba2Fe2F9, and BaFe2F7, were prepared through hydrothermal redox reactions. The characteristic structures of these compounds feature diverse distributions of FeIIF6 octahedra and FeIIIF6 groups. Ba7Fe7F34 contained one-dimensional infinite ∞[FeIIFeIII6F34]14- double chains, comprising cis corner-sharing octahedra along the b direction; Ba2Fe2F9 contained one-dimensional ∞[Fe2F9]4- double chains, consisting of cis corner-sharing octahedra along the chain (a-axis direction) and trans corner-sharing octahedra vertical to the chain, while BaFe2F7 revealed three-dimensional (3D) frameworks that consist of isolated edge-sharing dinuclear FeII2F10 units linked via corners by FeIIIF6 octahedra. Magnetization and Mössbauer spectroscopy measurements revealed that Ba7Fe7F34 exhibits an antiferromagnetic phase transition at ∼11 K, where ferrimagnetic ∞[FeIIFeIII6F34]14- double chains are arranged in a paralleling manner, while Ba2Fe2F9 shows canted antiferromagnetic ordering at ∼32.5 K, leading to noncollinear spin ordering.

Structural and Reactivity Effects of Secondary Metal Doping into Iron-Nitrogen-Carbon Catalysts for Oxygen Electroreduction

While improved activity was recently reported for bimetallic iron-metal-nitrogen-carbon (FeMNC) catalysts for the oxygen reduction reaction (ORR) in acid medium, the nature of active sites and interactions between the two metals are poorly understood. Here, FeSnNC and FeCoNC catalysts were structurally and catalytically compared to their parent FeNC and SnNC catalysts. While CO cryo-chemisorption revealed a twice lower site density of M-N_x sites for FeSnNC and FeCoNC relative to FeNC and SnNC, the mass activity of both bimetallic catalysts is 50-100% higher than that of FeNC due to a larger turnover frequency in the bimetallic catalysts. Electron microscopy and X-ray absorption spectroscopy identified the coexistence of Fe-N_x and Sn-N_x or Co-N_x sites, while no evidence was found for binuclear Fe-M-N_x sites. ⁵⁷Fe Mössbauer spectroscopy revealed that the bimetallic catalysts feature a higher D1/D2 ratio of the spectral signatures assigned to two distinct Fe-N_x sites, relative to the FeNC parent catalyst. Thus, the addition of the secondary metal favored the formation of D1 sites, associated with the higher turnover frequency.

Synthesis and Characterization of the Orthorhombic Sn3 O4 Polymorph

An unexplored tin oxide crystal phase (Sn₃ O₄ ) was experimentally synthesized via a facile hydrothermal method. After tuning the often-neglected parameters for the hydrothermal synthesis, namely the degree of filling of the precursor solution and the gas composition in the reactor head space, an unreported X-ray diffraction pattern was discovered. Through various characterization studies, such as Rietveld analysis, energy dispersive X-ray spectroscopy, and first-principles calculations, this novel material was characterized as orthorhombic mixed-valence tin oxide with the composition Sn^II ₂ Sn^IV O₄ . This orthorhombic tin oxide is a new polymorph of Sn₃ O₄ , which differs from the reported conventional monoclinic structure. Computational and experimental analyses showed that orthorhombic Sn₃ O₄ has a smaller band gap (2.0 eV), enabling greater absorption of visible light. This study is expected to improve the accuracy of hydrothermal synthesis and aid the discovery of new oxide materials.

Effect of the Deposition Time on the Structural, 3D Vertical Growth, and Electrical Conductivity Properties of Electrodeposited Anatase-Rutile Nanostructured Thin Films

TiO₂ time-dependent electrodeposited thin films were synthesized using an electrophoretic apparatus. The XRD analysis revealed that the films could exhibit a crystalline structure composed of ~81% anatase and ~6% rutile after 10 s of deposition, with crystallite size of 15 nm. AFM 3D maps showed that the surfaces obtained between 2 and 10 s of deposition exhibit strong topographical irregularities with long-range and short-range correlations being observed in different surface regions, a trend also observed by the Minkowski functionals. The height-based ISO, as well as specific surface microtexture parameters, showed an overall decrease from 2 to 10 s of deposition, showing a subtle decrease in the vertical growth of the films. The surfaces were also mapped to have low spatial dominant frequencies, which is associated with the similar roughness profile of the films, despite the overall difference in vertical growth observed. The electrical conductivity measurements showed that despite the decrease in topographical roughness, the films acquired a thickness capable of making them increasingly insulating from 2 to 10 s of deposition. Thus, our results prove that the deposition time used during the electrophoretic experiment consistently affects the films' structure, morphology, and electrical conductivity.

Inorganic Structural Chemistry of Titanium Dioxide Polymorphs

Apart from rutile, which crystallizes in the rutile-type structure characteristic of many metal dioxides, three major polymorphs of titanium dioxide (TiO₂) are known: anatase, brookite, and the α-lead dioxide (α-PbO₂)-type high-pressure form. Ti ions are commonly found in octahedra composed of six oxide ions, and their crystal structures are distinguished according to the linkage pattern of the TiO₆ octahedra. Inorganic structural chemistry considers that, in the rutile and α-PbO₂ types, Ti ions occupy half of the octahedral voids in the hexagonal close packing of oxide ions, and the TiO₆ octahedra in each layer are joined via edge sharing to form linear and zigzag strands, respectively. Anatase and brookite, on the other hand, exhibit more complex three-dimensional edge-sharing octahedral connections, although their origins are not fully explained. I show that these configurations can be interpreted as distinct stacking structures of layers with α-PbO₂-type zigzag strands. Additionally, I characterize the crystal structures of four TiO₂ polymorphs in detail using stacking sequence descriptions based on anion close packings and explore their relationships in terms of inorganic structural chemistry. I note that the moderate covalent nature of the Ti-O bond and the local structural instability of d⁰ ions result in an unusual variety of polymorphs in TiO₂.

Nonoxidative coupling of ethane with gold loaded photocatalysts

Direct and continuous conversion of ethane to yield n-butane and hydrogen at near room temperature (ca. 320 K) was examined with gold loaded gallium oxide and titanium dioxide photocatalysts without the aid of any oxidant in a flow reactor.

Exploring the structures, stability, and light absorption properties of three thiostannates synthesised at similar conditions

We present the synthesis, crystal structures and optical properties of three thiostannates prepared by using 1-(2-aminoethyl)piperazine (AEPz) as structure directing agent. Two of the thiostannates are layered materials (AEPz-SnS-1 and AEPz:EtOH-SnS-1) consisting of [Sn3S72-]n sheets with organic cations located in-between. The third compound is a molecular thiostannate (Sn2S6(AEPzH2)2) composed of dimeric Sn2S64- and AEPzH22+. In preparation of the layered compounds, the use of AEPz as the only solvent results in AEPz-SnS-1 with regular hexagonal pores and crystallographically disordered organic cations. In contrast, a mixture of AEPz and absolute ethanol gives AEPz:EtOH-SnS-1 with distorted hexagonal pores and ordered cations between the layers. The influence of cation order on the light absorption properties and the material thermal stability was investigated through thermal treatment of the layered compounds up to 200 °C. Both compounds show colour changes when heated, but cation order results in larger thermal stability. For AEPz-SnS-1, a decreased inter-layer distance and substantial loss of organic matter was observed when heated. However, pair distribution function analysis reveals that the local in-layer thiostannate structure of AEPz-SnS-1 remains unchanged. In contrast, AEPz:EtOH-SnS-1 does not undergo noticeable structural changes by the thermal treatment. All materials are optical semiconductors with band gaps of 3.0-3.1 eV.

Tin(II)-Induced Large Birefringence Enhancement in Metal Phosphates

Two alkali tin(II) phosphates, namely, Rb[SnF(HPO₄)] and Rb(Sn₃O)₂(PO₄)₃, were synthesized through mild hydrothermal methods. They belong to the orthorhombic Pnma and Pbcn space groups, respectively. Rb[SnF(HPO₄)] features a layered structure based on 1D [SnF(HPO₄)]_∞ chains interconnected by hydrogen bonds, with Rb⁺ cations located at the interlayer space. For Rb(Sn₃O)₂(PO₄)₃, each pair of [Sn₃O]⁴⁺ clusters is bridged by a pair of [P(1)O₄]^3- tetrahedra to build a 1D [Sn-P-O]_∞ chain. These 1D [Sn-P-O]_∞ chains are further cross-linked though [P(2)O₄]^3- tetrahedra to construct a 3D network with 7- and 10-membered-ring channels. The tin(II) ions in Rb[SnF(HPO₄)] and Rb(Sn₃O)₂(PO₄)₃ with stereochemically active lone pairs (SCALPs) significantly enhance the birefringences of metal phosphates: Δn = 0.147@1064 nm for Rb[SnF(HPO₄)] and 0.082@1064 nm for Rb(Sn₃O)₂(PO₄)₃.

Vibrational and optical identification of GeO2 and GeO single layers: a first-principles study

In the present work, the identification of two hexagonal phases of germanium oxides (namely GeO₂ and GeO) through the vibrational and optical properties is reported using density functional theory calculations. While structural optimizations show that single-layer GeO₂ and GeO crystallize in 1T and buckled phases, phonon band dispersions reveal the dynamical stability of each structure. First-order off-resonant Raman spectral predictions demonstrate that each free-standing single-layer possesses characteristic peaks that are representative for the identification of the germanium oxide phase. On the other hand, electronic band dispersion analysis shows the insulating and large-gap semiconducting nature of single-layer GeO₂ and GeO, respectively. Moreover, optical absorption, reflectance, and transmittance spectra obtained by means of G₀W₀-BSE calculations reveal the existence of tightly bound excitons in each phase, displaying strong optical absorption. Furthermore, the excitonic gaps are found to be at deep UV and visible portions of the spectrum, for GeO₂ and GeO crystals, with energies of 6.24 and 3.10 eV, respectively. In addition, at the prominent excitonic resonances, single-layers display high reflectivity with a zero transmittance, which is another indication of the strong light-matter interaction inside the crystal medium.

Syntheses and Characterization of the Mixed-Valent Manganese(II/III) Fluorides Mn2F5 and Mn3F8

We obtained single crystals of the binary mixed-valent fluorides Mn₂F₅ and Mn₃F₈ using a high-pressure/high-temperature approach. Mn₂F₅ crystallizes isotypic to CaCrF₅ in the monoclinic space group C2/c (No. 15), with a = 8.7078(8) Å, b = 6.1473(6) Å, c = 7.7817(7) Å, β = 117.41(1)°, V = 369.80(6) ų, Z = 4, and mC28 at T = 173 K. Mn₃F₈ crystallizes in the monoclinic space group P2₁ (No. 4) with a = 5.5253(2) Å, b = 4.8786(2) Å, c = 9.9124(4) Å, β = 92.608(2)°, V = 266.92(2) ų, Z = 2, and mP22 at T = 183 K and presents a new structure type. Crystal-chemical reasoning, CHARDI calculations, and quantum-chemical calculations allowed for the assignment of the oxidation states of the Mn atoms. In both bulk compounds, MnF₂ was present as an impurity, as evidenced by powder X-ray diffraction and IR and Raman spectroscopy.

Colossal Density-Driven Resistance Response in the Negative Charge Transfer Insulator MnS_{2}

A reversible density driven insulator to metal to insulator transition in high-spin MnS_{2} is experimentally observed, leading with a colossal electrical resistance drop of 10^{8}  Ω by 12 GPa. Density functional theory simulations reveal the metallization to be unexpectedly driven by previously unoccupied S_{2}^{2-} σ_{3p}^{*} antibonding states crossing the Fermi level. This is a unique variant of the charge transfer insulator to metal transition for negative charge transfer insulators having anions with an unsaturated valence. By 36 GPa the emergence of the low-spin insulating arsenopyrite (P2_{1}/c) is confirmed, and the bulk metallicity is broken with the system returning to an insulative electronic state.

BSSE-corrected consistent Gaussian basis sets of triple-zeta valence with polarization quality of the sixth period for solid-state calculations

Consistent basis sets of triple-zeta valence with polarization quality for the elements Cs-Po were derived for periodic quantum-chemical solid-state calculations. They are an extension of the pob-TZVP-rev2 [Vilela Oliveira, D.; Laun, J.; Peintinger, M. F. and Bredow, T., J. Comput. Chem., 2019, 40 (27), 2364-2376] basis sets and are based on the fully relativistic effective core potentials (ECPs) of the Stuttgart/Cologne group and on the def2-TZVP valence basis of the Ahlrichs group. The basis sets are constructed to minimize the basis set superposition error (BSSE) in crystalline systems. The contraction scheme, the orbital exponents, and contraction coefficients were optimized in order to ensure robust and stable self-consistent-field (SCF) convergence for a set of compounds and metals. For the applied PW1PW hybrid functional, the average deviations of the calculated lattice constants from experimental references are smaller with pob-TZVP-rev2 than with standard basis sets available from the CRYSTAL basis set database.

Facet controlled growth mechanism of SnO2 (101) nanosheet assembled film via cold crystallization

Cold crystallization of SnO₂ was realized in aqueous solutions, where crystal growth was controlled to form SnO₂ (101) nanosheet assembled films for devices such as chemical sensors. The nanosheets grew directly on a fluorine-doped tin oxide substrate without a seed layer or a buffer layer. The nanosheets had a thickness of 5–10 nm and an in-plane size of 100–1600 nm. Moreover, the large flat surface of the (101) facet was metastable. The thickness of the SnO₂ (101) nanosheet assembled film was approximately 800 nm, and the film had a gradient structure that contained many connected nanosheets. TEM results revealed that the predominate branch angles between any two connected nanosheets were 90° and 46.48°, corresponding to type I and type II connections, respectively. These connections were consistent with the calculations based on crystallography. Crystallographic analysis clarified the characteristic crystal growth of the SnO₂ (101) nanosheet assembled film in the aqueous solution. Furthermore, we demonstrate that the metastable (101) facet can be exploited to control the rate of crystal growth by adjusting the etching condition.

Orbital Design of Two-Dimensional Transition-Metal Peroxide Kagome Crystals with Anionogenic Dirac Half-Metallicity

Assembling p orbital ferromagnetic half-metallicity and a topological element, such as a Dirac point at the Fermi level, in a single nanomaterial is of particular interest for long-distance, high-speed, and spin-coherent transportation in nanoscale spintronic devices. On the basis of the tight-binding model, we present an orbital design of a two-dimensional (2D) anionogenic Dirac half-metal (ADHM) by patterning cations with empty d orbitals and anions with partially filled p-type orbitals into a kagome lattice. Our first-principles calculations show that 2D transition-metal peroxides h-TM₂(O₂)₃ (TMO₃, TM = Ti, Zr, Hf), containing group IVB transition-metal cations [TM]⁴⁺ bridged with dioxygen anions [O₂]^8/3- in a kagome structure, are stable ADHMs with a Curie temperature over 103 K. The 2/3 filled π* orbitals of dioxygen anions are ferromagnetically coupled, leading to p orbital ferromagnetism and a half-metallic Dirac point right at the Fermi level with a Fermi velocity reaching 2.84 × 10⁵ m/s. We proposed that 2D h-TM₂(O₂)₃ crystals may be extracted from ABO₃ bulk materials containing 2D TMO₃ layers.

Inside the failure mechanism of tin oxide as anode for sodium ion batteries

The conversion-alloying compounds have been identified as promising anode materials for sodium ion batteries (SIBs). One of them, SnO2, with an enormous theoretical capacity of 1558 mAh g−1 is an interesting candidate, also due to its low cost, environmental friendliness and wide availability of tin. However, many drawbacks limit its application in commercial batteries. In this paper, SnO2 has been synthesized from cheap reagents by using simple and easily scalable coprecipitation synthesis routes obtaining nanoparticles with sizes between 2 and 14 nm with almost spherical morphologies. The reasons of the failure of the alloying/de-alloying process were investigated by combining the results obtained from common electrochemical techniques, providing useful examples for the investigation of every material with analogous electrochemical features. Thanks to cyclic voltammetry, different reaction paths were detected for the two samples. The first cycle irreversibility was well characterized with electrochemical impedance spectroscopy, showing interesting trends in the values of the resistance. Galvanostatic cycling with potential limitations was employed to quantify the irreversibility, finding out that the most crystalline sample reached the terminal phase in the Sn-Na system (Na15Sn4), while the least crystalline sample could not achieve such a result (Na3Sn). The crystallinity of SnO2 was determined to be a key parameter, often neglected, for the realization of satisfactory anode compounds.

Maghemite in Brazilian Iron Ores: Quantification of the Magnetite-Maghemite Isomorphic Series by Χ-ray Diffraction and the Rietveld Method, and Confirmation by Independent Methods

Maghemite (γ-Fe2O3) is a mineral formed from magnetite oxidation at low temperatures, an intermediate metastable term of the magnetite to hematite oxidation and could be mixed with both. It has magnetic susceptibility similar to magnetite, crystal structure close to magnetite with which it forms a solid solution, while compositionally it equals hematite. Maghemite is thus easily misidentified as magnetite by Χ-ray diffraction and/or as hematite by spot chemical analysis in iron ore characterization routines. Nonstoichiometric magnetite could be quantified in samples of Brazilian soils and iron ores by the Rietveld method using a constrained refinement of the Χ-ray patterns. The results were confirmed by reflected light microscopy and Raman spectroscopy, thus qualitatively validating the method. Χ-ray diffraction with the refinement of the isomorphic substitution of Fe2+ by Fe3+ along the magnetite-maghemite solid solution could help to suitably characterize maghemite in iron ores, allowing for the evaluation of its ultimate influence on mineral processing, as its effect on surface and breakage properties.

Colossal Spin Splitting in the Monolayer of the Collinear Antiferromagnet MnF2

In this Letter we report on the colossal spin splitting (on the order of several electronvolts) in the collinear antiferromagnetic (AFM) MnF₂ (110) monolayer, which we obtained from first-principles calculations and explain in terms of group-theoretical analysis. This Pekar-Rashba AFM-induced spin splitting with a magnetic mechanism does not require the presence of spin-orbit coupling such as with a traditional Rashba-Dresselhaus electric mechanism. Furthermore, it was observed for all wave vectors, including high-symmetry points of the two-dimensional (2D) Brillouin zone. This is in contrast to recently reported AFM-induced spin splitting in the bulk structure of MnF₂, which was both smaller by at least an order of magnitude and required to vanish by symmetry at several high-symmetry points and directions of the three-dimensional Brillouin zone. The crucial part of our group-theoretical analysis is the determination of the magnetic layer group for the monolayer structure for which we propose a simple and generic procedure.

Ferromagnetic alloy for high-efficiency photovoltaic conversion in solar cells: first-principles insights when doping SnO2 rutile with coupled Eu-Gd

From results of first-principles all-electron full-potential augmented spherical-wave calculations within a generalized gradient approximation, a materials design for half-metallic ferromagnetic semiconductors based on (Eu,Gd)-doped SnO2 rutile is proposed. Moreover, their half-metallic ferromagnetic properties are homogenous and energetically stable for different crystallographic directions. Therefore, the interatomic exchange interaction between the spins of double impurity ions is a long-range ferromagnetic interaction that is sharply weakened when the distance between Eu-Gd increases. The double impurities most likely substitute adjacent Sn sites and result in strong ferromagnetic interactions by p-f hybridization between rare earth 4f and Op states. There is great interest in the configuration that has the lowest energy difference, where the double impurity substitutes the nearest neighbor Sn sites along the z-axis of SnO2 rutile. Generalized gradient approximation GGA and GGA+U calculations were performed. According to our revPBE-GGA calculations, the ferromagnetic compound is capable of absorbing 96% from the visible light. Furthermore, the transport properties at room temperature ensure excellent electrical conductivity, low thermal conductivity, and the most optimal figure of merit (ZT), which leads to high thermoelectric performance. As the latter are closely related to free flow charge carriers, we can subsequently predict that the ferromagnetic alloy will be able to be a great power source for highly effective photovoltaic conversion in solar cells. Further experimentation will be necessary to obtain confirmation of our ab initio predictions.

F-doping of nanostructured ZnO: a way to modify structural, electronic, and surface properties

Polycrystalline ZnO is a material often used in heterogeneous catalysis. Its properties can be altered by the addition of dopants. We used gaseous fluorine (F_2(g)) as direct way to incorporate fluoride in ZnO as anionic dopants. Here, the consequences of this treatment on the structural and electronic properties, as well as on the acidic/basic sites of the surface, are investigated. It is shown that the amount of F incorporation into the structure can be controlled by the synthesis parameters (t, T, p). While the surface of ZnO was altered as shown by, e.g., IR spectroscopy, XPS, and STEM/EDX measurements, the F₂ treatment also influenced the electronic properties (optical band gap, conductivity) of ZnO. Furthermore, the Lewis acidity/basicity of the surface was affected which is evidenced by using, e.g., different probe molecules (CO₂, NH₃). In situ investigations of the fluorination process offer valuable insights on the fluorination process itself.

A Novel High-Pressure Tin Oxynitride Sn2 N2 O

We report the first oxynitride of tin, Sn2 N2 O (SNO), exhibiting a Rh2 S3 -type crystal structure with space group Pbcn. All Sn atoms are in six-fold coordination, in contrast to Si in silicon oxynitride (Si2 N2 O) and Ge in the isostructural germanium oxynitride (Ge2 N2 O), which appear in four-fold coordination. SNO was synthesized at 20 GPa and 1200-1500 °C in a large volume press. The recovered samples were characterized by synchrotron powder X-ray diffraction and single-crystal electron diffraction in the TEM using the automated diffraction tomography (ADT) technique. The isothermal bulk modulus was determined as Bo =193(5) GPa by using in-situ synchrotron X-ray diffraction in a diamond anvil cell. The structure model is supported by DFT calculations. The enthalpy of formation, the bulk modulus, and the band structure have been calculated.

Preserving the Exposed Facets of Pt3Sn Intermetallic Nanocubes During an Order to Disorder Transition Allows the Elucidation of the Effect of the Degree of Alloy Ordering on Electrocatalysis

Controlling which facets are exposed in nanocrystals is crucial to understanding different activity between ordered and disordered alloy electrocatalysts. We modify the degree of ordering of Pt₃Sn nanocubes, while maintaining the shape and size, to enable a direct evaluation of the effect of the order on ORR catalytic activity. We demonstrate a 2.3-fold enhancement in specific activity by 60- and 30%-ordered Pt₃Sn nanocubes compared to 95%-ordered. This was shown to be likely due to surface vacancies in the less-ordered particles. The greater order, however, results in higher stability of the electrocatalyst, with the more disordered nanoparticles showing the dissolution of tin and platinum species during electrocatalysis.

Continuous flow hydrothermal synthesis of phase pure rutile TiO2 nanoparticles with a rod-like morphology

Titania nanocrystals are used in numerous applications but specific polymorphs (anatase, rutile, brookite) are typically required in specific applications making synthesis control over the crystal phase essential. Supercritical continuous flow reactors constitute fast, scalable alternatives to conventional autoclave hydrothermal synthesis. They provide outstanding control over nanoparticle characteristics such as size, crystallinity, and morphology but previous studies have always resulted in anatase products. Here we report, for the first time, a continuous hydrothermal flow method for obtaining phase pure rutile nanoparticles thereby significantly broadening the crystal design space for large scale titania applications. Through variation of the reactor temperature, the dimensions of the rod-like rutile crystallites are tunable in a range of 35 to 60 nm in length and 10 to 35 nm in width (maximum aspect ratio of ∼3.5) leading to a tunable band gap (3.2-3.5 eV) and high specific surface areas exceeding 200 m² g^-1.

Room-temperature solution-phase epitaxial nucleation of PbS quantum dots on rutile TiO2 (100)

Owing to its simplicity and versatility, the successive ionic layer adsorption and reaction (SILAR) method is increasingly being employed to develop low-cost hetero-nanostructured sensitized oxide systems for solar energy conversion, such as solar cells and solar fuels schemes. Understanding the nature of the SILAR quantum dot (QD) nucleation and growth on an insulating oxide is then critical as it will determine the QD density and spatial distribution, as well as the optoelectronic properties of the QD/oxide interfaces (e.g. QD bandgap onset). Here, we demonstrate epitaxial nucleation of lead sulfide (PbS) QDs onto a planar rutile titanium dioxide (100) surface employing the SILAR method. The QDs nucleated by SILAR are crystalline structures characterized by a truncated pyramidal shape, with nucleation occurring preferentially along the rutile (010) and (001) crystal orientations. The PbS QD size distribution is constrained by lattice mismatch causing strain in the lead sulfide. These results highlight the potential of SILAR for the facile growth of high-quality epitaxial nanostructures in liquid phase, under ambient conditions and at room temperature.

Observation of 9-Fold Coordinated Amorphous TiO2 at High Pressure

Knowledge of the structure in amorphous dioxides is important in many fields of science and engineering. Here we report new experimental results of high-pressure polyamorphism in amorphous TiO₂ (a-TiO₂). Our data show that the Ti coordination number (CN) increases from 7.2 ± 0.3 at ∼16 GPa to 8.8 ± 0.3 at ∼70 GPa and finally reaches a plateau at 8.9 ± 0.3 at ≲86 GPa. The evolution of the structural changes under pressure is rationalized by the ratio (γ) of the ionic radius of Ti to that of O. It appears that the CN ≈ 9 plateau correlates with the two 9-fold coordinated polymorphs (cotunnite, Fe₂P) with different γ values. This CN-γ relationship is compared with those of a-SiO₂ and a-GeO₂, displaying remarkably consistent behavior between CN and γ. The unified CN-γ relationship may be generally used to predict the compression behavior of amorphous AO₂ compounds under extreme conditions.

Visible-Light Active Titanium Dioxide Nanomaterials with Bactericidal Properties

This article provides an overview of current research into the development, synthesis, photocatalytic bacterial activity, biocompatibility and cytotoxic properties of various visible-light active titanium dioxide (TiO2) nanoparticles (NPs) and their nanocomposites. To achieve antibacterial inactivation under visible light, TiO2 NPs are doped with metal and non-metal elements, modified with carbonaceous nanomaterials, and coupled with other metal oxide semiconductors. Transition metals introduce a localized d-electron state just below the conduction band of TiO2 NPs, thereby narrowing the bandgap and causing a red shift of the optical absorption edge into the visible region. Silver nanoparticles of doped TiO2 NPs experience surface plasmon resonance under visible light excitation, leading to the injection of hot electrons into the conduction band of TiO2 NPs to generate reactive oxygen species (ROS) for bacterial killing. The modification of TiO2 NPs with carbon nanotubes and graphene sheets also achieve the efficient creation of ROS under visible light irradiation. Furthermore, titanium-based alloy implants in orthopedics with enhanced antibacterial activity and biocompatibility can be achieved by forming a surface layer of Ag-doped titania nanotubes. By incorporating TiO2 NPs and Cu-doped TiO2 NPs into chitosan or the textile matrix, the resulting polymer nanocomposites exhibit excellent antimicrobial properties that can have applications as fruit/food wrapping films, self-cleaning fabrics, medical scaffolds and wound dressings. Considering the possible use of visible-light active TiO2 nanomaterials for various applications, their toxicity impact on the environment and public health is also addressed.

Tuning the CrIV/CrIII Valence States in Purple Cr-Doped SnO2 Nanopowders: The Key Role of CrIV Centers and Defects

A low content of chromium (≤5 mol %) has been incorporated into a SnO₂ cassiterite by a coprecipitation route in a basic medium, followed by an annealing step under an O₂ flow at T = 800 °C and T = 1000 °C. Accurate UV-vis and EPR spectroscopy investigations show the coexistence of isolated Cr⁴⁺ and Cr³⁺ ions as well as ferromagnetic Cr⁴⁺-Cr³⁺ and antiferromagnetic Cr³⁺-Cr³⁺ interactions. The strong purple hue is related to the isolated Cr⁴⁺ ions stabilized in a distorted octahedral site. This is thanks to the second-order Jahn-Teller (SOJT) effect with a crystal field splitting 10Dq value around 2.4 eV, whereas the 10Dq value is around 2 eV for isotropic Cr³⁺ ions, partially substituted for Sn⁴⁺ ions in cassiterite. Just after the coprecipitation process, only Cr³⁺ species are stabilized in this rutile network with a poor crystallinity. The isolated Cr⁴⁺ content remains high after annealing at 800 °C for 2 days especially for the highest Cr rate (2 and 5 mol %), leading to a darker purple color, but unfortunately the Cr³⁺ content also increases for a higher Cr concentration. A lighter purple hue can be reached after calcination at a higher temperature (T = 1000 °C) for a shorter time (4 h) but with a lower Cr content to avoid Cr clusters. This is due to stabilizing a high content of isolated Cr⁴⁺ species and limiting the Cr⁴⁺-Cr³⁺ ferromagnetic interactions, which are optimal for a 2% Cr content and also cause the color to darken. The key roles of the Cr⁴⁺ rate and the Cr⁴⁺-Cr³⁺ clusters create local defects whose concentration strongly varies with a total Cr content, which have then been demonstrated to strongly influence the optical and magnetic properties.

Modulating Activity through Defect Engineering of Tin Oxides for Electrochemical CO2 Reduction

The large-scale application of electrochemical reduction of CO2, as a viable strategy to mitigate the effects of anthropogenic climate change, is hindered by the lack of active and cost-effective electrocatalysts that can be generated in bulk. To this end, SnO2 nanoparticles that are prepared using the industrially adopted flame spray pyrolysis (FSP) technique as active catalysts are reported for the conversion of CO2 to formate (HCOO-), exhibiting a FEHCOO - of 85% with a current density of -23.7 mA cm-2 at an applied potential of -1.1 V versus reversible hydrogen electrode. Through tuning of the flame synthesis conditions, the amount of oxygen hole center (OHC; Sn≡O●) is synthetically manipulated, which plays a vital role in CO2 activation and thereby governing the high activity displayed by the FSP-SnO2 catalysts for formate production. The controlled generation of defects through a simple, scalable fabrication technique presents an ideal approach for rationally designing active CO2 reduction reactions catalysts.

Structural changes during water-mediated amorphization of semiconducting two-dimensional thio-stannates

Owing to their combined open-framework structures and semiconducting properties, two-dimensional thio-stannates show great potential for catalytic and sensing applications. One such class of crystalline materials consists of porous polymeric [Sn3S7 2-] n sheets with molecular cations embedded in-between. The compounds are denoted R-SnS-1, where R is the cation. Dependent on the cation, some R-SnS-1 thio-stannates transition into amorphous phases upon dispersion in water. Knowledge about the fundamental chemical properties of the thio-stannates, including their water stability and the nature of the amorphous products, has not yet been established. This paper presents a time-resolved study of the transition from the crystalline to the amorphous phase of two violet-light absorbing thio-stannates, i.e. AEPz-SnS-1 [AEPz = 1-(2-amino-ethyl)-piperazine] and trenH-SnS-1 [tren = tris-(2-amino-ethyl)-amine]. X-ray total scattering data and pair distribution function analysis reveal no change in the local intralayer coordination during the amorphization. However, a rapid decrease in the crystalline domain sizes upon suspension in water is demonstrated. Although scanning electron microscopy shows no significant decrease of the micrometre-sized particles, transmission electron microscopy reveals the formation of small particles (∼200-400 nm) in addition to the larger particles. The amorphization is associated with disorder of the thio-stannate nanosheet stacking. For example, an average decrease in the interlayer distance (from 19.0 to 15.6 Å) is connected to the substantial loss of the organic components as shown by elemental analysis and X-ray photoelectron spectroscopy. Despite the structural changes, the light absorption properties of the amorphisized R-SnS-1 compounds remain intact, which is encouraging for future water-based applications of such materials.

Tin titanate-the hunt for a new ferroelectric perovskite

We review all the published literature and show that there is no experimental evidence for homogeneous tin titanate SnTiO₃ in bulk or thin-film form. Instead a combination of unrelated artefacts are easily misinterpreted. The x-ray Bragg data are contaminated by double scattering from the Si substrate, giving a strong line at the 2θ angle exactly where perovskite SnTiO₃ should appear. The strong dielectric divergence near 560 K is irreversible and arises from oxygen site detrapping, accompanied by Warburg/Randles interfacial anomalies. The small (4 µC cm^-2) apparent ferroelectric hysteresis remains in samples shown to be pure (Sn,Ti)O₂ rutile/cassiterite, in which ferroelectricity is forbidden. Only very recent work reveals real bulk SnTiO₃, but it possesses an ilmenite-like structure with an elaborate array of stacking faults, not suitable for ferroelectric devices. Unpublished TEM data reveal an inhomogeneous SnO layered structured thin films, related to shell-core structures. The harsh conclusion is that there is a combination of unrelated artefacts masquerading as ferroelectricity in powders and ALD films; and only a trace of a second phase in PLD film data suggests any perovskite content at all. The fact that x-ray, dielectric, and hysteresis data all lead to the wrong conclusion is instructive and reminds us of earlier work on copper calcium titanate (a well-known boundary-layer capacitor).

Crystal-Plane Dependence of Nb-Doped Rutile TiO2 Single Crystals on Photoelectrochemical Water Splitting

The crystal-plane dependence of the photoelectrochemical (PEC) water-splitting property of rutile-structured Nb-doped TiO2 (TiO2:Nb) single-crystal substrates was investigated. Among the crystal planes, the (001) plane was a very promising surface for attaining good photocurrent. Under 1 sun illumination at 1.5 V vs. a reversible hydrogen electrode, the TiO2:Nb(001) single-crystal substrate showed the highest photocurrent (0.47 mA/cm2) among the investigated substrates. The doped Nb ions were segregated inward from the top surface, and the TiO2 ultrathin layer was formed at the surface of the crystal, resulting in the formation of a heterointerface between the TiO2 and the TiO2:Nb. The enhancement of the PEC properties of the TiO2:Nb(001) single-crystal substrate originated from favorable atomic configurations for water molecule absorption and facilitation of transport of photoexcited electron–hole pairs in the depletion layer formed around the heterointerface of TiO2 thin layers on the base crystal.

Using a machine learning approach to determine the space group of a structure from the atomic pair distribution function

A method is presented for predicting the space group of a structure given a calculated or measured atomic pair distribution function (PDF) from that structure. The method utilizes machine learning models trained on more than 100 000 PDFs calculated from structures in the 45 most heavily represented space groups. In particular, a convolutional neural network (CNN) model is presented which yields a promising result in that it correctly identifies the space group among the top-6 estimates 91.9% of the time. The CNN model also successfully identifies space groups for 12 out of 15 experimental PDFs. Interesting aspects of the failed estimates are discussed, which indicate that the CNN is failing in similar ways as conventional indexing algorithms applied to conventional powder diffraction data. This preliminary success of the CNN model shows the possibility of model-independent assessment of PDF data on a wide class of materials.

Phase Dynamics on Conversion-Reaction-Based Tin-Doped Ferrite Anode for Next-Generation Lithium Batteries

The conventional view of conversion reaction is based on the reversibility, returning to an initial material structure through reverse reaction at each cycle in cycle life, which impedes the complete understanding on a working mechanism upon a progression of cycles in conversion-reaction-based battery electrodes. Herein, a series of tin-doped ferrites (Fe_{3- x}Sn _xO₄, x = 0-0.36) are prepared and applied to a lithium-ion battery anode. By achieving the ideal reoxidation into SnO₂, the Fe_2.76Sn_0.24O₄ composite anchored on reduced graphene oxide shows a high reversible capacity of 1428 mAh g^-1 at 200 mA g^-1 after 100 cycles, which is the best performance of Sn-based anode materials so far. Significantly, a newly formed γ-FeOOH phase after 100 cycles is identified from topological features through synchrotron X-ray absorption spectroscopy with electronic and atomic structural information, suggesting the phase transformation from magnetite to lepidocrocite upon cycling. Contrary to the conventional view, our work suggests a variable working mechanism in an iron-based composite with the dynamic phases from iron oxide to iron oxyhydroxide in the battery cycle life, based on the reactivity of metal nanoparticles formed during reaction toward the solid electrolyte interface layer.

Tetravalent lead in nature – plattnerite crystals from Mine du Pradet (France) and Mount Trevasco (Italy)

Natural lead dioxide samples (β modification) from Cap Garonne, Mine du Pradet, France and Mount Trevasco, Italy were studied by single crystal X-ray and electron diffraction, clearly manifesting the rutile-type structure. A needle from the Mount Trevasco sample was investigated on a single crystal diffractometer: P42/mnm, a = 495.81(10), c = 338.66(7) pm, wR = 0.0513, 117 F 2 values (all data) and nine variables (293 K data). An additional data set at T = 90 K gave no hint for structural distortions.