Strontium ferromolybdate, Sr2FeMoO6, is an important member of the family of double perovskites with the possible technological applications in the field of spintronics and solid oxide fuel cells. Its preparation via a multi-step ceramic route or various wet chemistry-based routes is notoriously difficult. The present work demonstrates that Sr2FeMoO6 can be mechanosynthesized at ambient temperature in air directly from its precursors (SrO, α-Fe, MoO3) in the form of nanostructured powders, without the need for solvents and/or calcination under controlled oxygen fugacity. The mechanically induced evolution of the Sr2FeMoO6 phase and the far-from-equilibrium structural state of the reaction product are systematically monitored with XRD and a variety of spectroscopic techniques including Raman spectroscopy, 57Fe Mössbauer spectroscopy, and X-ray photoelectron spectroscopy. The unique extensive oxidation of iron species (Fe0 → Fe3+) with simultaneous reduction of Mo cations (Mo6+ → Mo5+), occuring during the mechanosynthesis of Sr2FeMoO6, is attributed to the mechanically triggered formation of tiny metallic iron nanoparticles in superparamagnetic state with a large reaction surface and a high oxidation affinity, whose steady presence in the reaction mixture of the milled educts initiates/promotes the swift redox reaction. High-resolution transmission electron microscopy observations reveal that the mechanosynthesized Sr2FeMoO6, even after its moderate thermal treatment at 923 K for 30 min in air, exhibits the nanostructured nature with the average particle size of 21(4) nm. At the short-range scale, the nanostructure of the as-prepared Sr2FeMoO6 is characterized by both, the strongly distorted geometry of the constituent FeO6 octahedra and the extraordinarily high degree of anti-site disorder. The degree of anti-site disorder ASD = 0.5, derived independently from the present experimental XRD, Mössbauer, and SQUID magnetization data, corresponds to the completely random distribution of Fe3+ and Mo5+ cations over the sites of octahedral coordination provided by the double perovskite structure. Moreover, the fully anti-site disordered Sr2FeMoO6 nanoparticles exhibit superparamagnetism with the blocking temperature TB = 240 K and the deteriorated effective magnetic moment μ = 0.055 μB per formula unit.

Nanocrystalline M1-xPbxF2 (M = Ca, Sr, Ba) solid solutions were prepared by ball milling mixtures of binary parent materials. The structure of the obtained materials was investigated by 19F MAS NMR spectroscopy and XRPD, and their ionic conductivity by impedance spectroscopy. It was found that fluorite-structured solid solutions over the whole range of compositions can be prepared by ball milling for all three systems, closing the broad miscibility gap of the CaF2-PbF2 system. The fluoride ion conductivity increased with increasing Pb content of the solid solutions, with Ba0.10Pb0.90F2 showing the highest conductivity of all samples prepared, being 1.5 orders of magnitude smaller than the one of PbSnF4. Ca1-xPbxF2 showed a fluoride ion conductivity increase which can be assigned to geometric frustration induced disorder. Ball milling of pure PbF2 revealed an increase of the fluoride ion conductivity by 2.5 orders of magnitude in the case of PbF2 containing a large amount of β-PbF2 compared to microcrystalline β-PbF2. Its fluoride ion conductivity is also 2.5 orders of magnitude larger than the fluoride ion conductivity of ball milled PbF2 consisting of a small amount of β-PbF2 but a large amount of α-PbF2 pointing to differently conducting and structured grain boundaries of α-PbF2 and β-PbF2.

For the first time, a multi-anionic and multi-cationic high entropy oxyhalide is presented as high capacity cathode for Li-ion batteries.

Starting from gelatinous aluminum chloride hydroxide, the transformation process toward alpha-Al2O3 was examined using Al-27 NMR, both in the liquid and solid states, as a main analytical tool. By increasing the hydrolysis ratio (h, defined as [OH-]/[Al3+]) of the starting aqueous precursor up to h = 2.5, the transition temperature to the final product, alpha-Al2O3, decreased to as low as 500 degrees C. In this case, the structural change from amorphous alumina to alpha-Al2O3 took place without intermediate transition Al2O3 phases. Examining the process of networking during the transition from aqueous sol-through the state of xerogel-to final anhydrous oxide by nuclear magnetic resonance (NMR) revealed the presence of highly polymeric species mainly ascribed to delta-[Al2O8Al28(OH)(56)(H2O)(24)](18+) (delta-Al-30). delta-Al-30 species were found in the solution phase and became predominant after drying. We conclude that the lower temperature synthesis of alpha-Al2O3 became possible due to preformation of polymerized AlO6 construction units in the precursor, reducing the energy barrier for the nucleation of the final alpha-Al2O3 phase.

As a case study for the evaluation of the nanostructure of layered materials, we report on results of the comprehensive characterization of high-energy ball-milled layered molybdenum disulfide (2H-MoS2) on different length scales. Analysis of X-ray powder diffraction patterns (XRPDs) including the Debye background at low scattering angles caused by uncorrelated single or few-layer MoS2 slabs (full scattering model), yield much more precise data about the average stacking degree than routine XRPD evaluation, and an estimation of the amount of single layer material is possible. Reflections with super Lorentzian line shape can be satisfactorily modeled assuming different stacking sequences induced by the mechanical forces exerted during the high-energy ball-mill process. An advanced analysis of UV-Vis spectra to determine layer number and lateral crystallite size, which was recently developed for liquid exfoliation materials, is used for the first time, and the results demonstrate the universal applicability of the approach. The data obtained with this analysis support the main findings of evaluation of the XRPD data. Both methods clearly evidence that increasing the duration of high-energy ball-mill treatment leads to an increase of material with decreasing average stacking and a reduction of the lateral size of the slabs. Finally, high-resolution transmission electron microscopy enabled identification of defects which can hardly be detected in XRPDs or in UV-Vis spectra.

Ba1-xCaxF2 samples with fluorite-type structure were prepared by high-energy ball milling. DSC measurements revealed exothermic decomposition at temperatures of about 450 degrees C. Decomposition was also observed by high temperature X-ray experiments. As a product, two phases with compositions close to pure BaF2 and CaF2 were obtained. The decomposition temperature observed by X-ray measurements is lower than in the DSC experiments. This might indicate that X-ray irradiation could foster the decomposition.

The defect density of a material is central to its properties. Here, we show, employing EXAFS measurements and MD simulation, how the Ba-Li antisite defect density of perovskite-structured BaLiF3 nanoparticles can be tuned. In particular, we show that ball milling reduces the defect content. Conversely, thermal annealing increases the defect density. The work represents a first step toward tailoring the properties of a material via defect tuning postsynthesis.

In the solid solution series Li2-x Ge3+1/2xSb2Te7 and Li2-xGe11+1/2xSb2Te15 (0 <= x <= 2), the heterovalent substitution gradually changes the vacancy concentration on the cation position from 0% (for x = 0) to 14.3% and 6.67%, respectively. Fewer vacancies extend the stability range of the rocksalt-type high-temperature phase to lower temperatures, which is favorable for thermoelectric applications. Further differences in thermoelectric properties correlate with the Li/Ge ratio. The phononic part of thermal conductivity decreases with increasing Li content and all Li-containing compounds exhibit enhanced thermoelectric figures of merit zT compared to their Li-free parent phases with a maximum zT value of 1.9 for LiGe3.5Sb2Te7 at 450 degrees C. Li-7 solid state NMR reveals high Li mobility at elevated temperatures. Thus, lithium germanium antimony tellurides can be considered as new member of phonon liquid electron-crystal (PLEC) thermoelectric materials with superior thermoelectric properties.

In many cases, limitations in conventional synthesis routes hamper the accessibility to materials with properties that have been predicted by theory. For instance, metastable compounds with local non-equilibrium structures can hardly be accessed by solid-state preparation techniques often requiring high synthesis temperatures. Also other ways of preparation lead to the thermodynamically stable rather than metastable products. Fortunately, such hurdles can be overcome by mechanochemical synthesis. Mechanical treatment of two or three starting materials in high-energy ball mills enables the synthesis of not only new, metastable compounds but also of nanocrystalline materials with unusual or enhanced properties such as ion transport. In this short review we report about local structures and ion transport of oxides and fluorides mechanochemically prepared by high-energy ball-milling.

Ionic conductivity is ubiquitous to many industrially important applications such as fuel cells, batteries, sensors, and catalysis. Tunable conductivity in these systems is therefore key to their commercial viability. Here, we show that geometric frustration can be exploited as a vehicle for conductivity tuning. In particular, we imposed geometric frustration upon a prototypical system, CaF2, by ball milling it with BaF2, to create nanostructured Ba1-xCaxF2 solid solutions and increased its ionic conductivity by over 5 orders of magnitude. By mirroring each experiment with MD simulation, including "simulating synthesis", we reveal that geometric frustration confers, on a system at ambient temperature, structural and dynamical attributes that are typically associated with heating a material above its superionic transition temperature. These include structural disorder, excess volume, pseudovacancy arrays, and collective transport mechanisms; we show that the excess volume correlates with ionic conductivity for the Ba1-xCaxF2 system. We also present evidence that geometric frustration-induced conductivity is a general phenomenon, which may help explain the high ionic conductivity in doped fluorite-structured oxides such as ceria and zirconia, with application for solid oxide fuel cells. A review on geometric frustration [ Nature 2015 , 521 , 303 ] remarks that classical crystallography is inadequate to describe systems with correlated disorder, but that correlated disorder has clear crystallographic signatures. Here, we identify two possible crystallographic signatures of geometric frustration: excess volume and correlated "snake-like" ionic transport; the latter infers correlated disorder. In particular, as one ion in the chain moves, all the other (correlated) ions in the chain move simultaneously. Critically, our simulations reveal snake-like chains, over 40 Å in length, which indicates long-range correlation in our disordered systems. Similarly, collective transport in glassy materials is well documented [for example, J. Chem. Phys. 2013 , 138 , 12A538 ]. Possible crystallographic nomenclatures, to be used to describe long-range order in disordered systems, may include, for example, the shape, length, and branching of the "snake" arrays. Such characterizations may ultimately provide insight and differences between long-range order in disordered, amorphous, or liquid states and processes such as ionic conductivity, melting, and crystallization.

Abstract In this contribution we report on the development and application of modern NMR approaches for the in situ characterization of the crystallization of metastable materials. The work was performed within the framework of the DFG priority programme SPP 1415 “Crystalline Non-Equilibrium Phases”. As one of the goals of this project, the development of a NMR methodology which enables an analysis of local structural motifs on short (1–2 Å) and extended (2–6 Å) length scales without the need for fast magic angle spinning (MAS) has been defined, since the enormous centripetal forces which occur during fast sample rotation (up to 107 g) may intervene with the chemical or physical process which is being monitored. To achieve this goal, we developed a magic angle turning probe and pulse sequences allowing to trace the isotropic chemical shifts and heteronuclear dipolar couplings and hence the determination of structural motifs on short and intermediate length scales. With the implementation of novel inductive heating approaches the range of accessible rotation frequencies for in situ high temperature NMR measurements has been enlarged, now covering the νMAS range of 0–10 kHz with an accessible temperature of up to 700°C. Application of NMR methodologies for the characterization of crystallization processes and the structure and dynamics of novel phases, partially in joint collaborations within the priority program, are also reported.

We present a novel approach to the solid-state synthesis of garnet-type cubic Li7La3Zr2O12 (c-LLZO) nanostructured particles with 1.0 mass% Al at 750 C within 3 h. In contrast to conventional solid-state processes, a highly reactive precursor was prepared in two steps: (i) by homogenizing the stoichiometric mixture without Li, and (ii) subsequent addition of Li in the form of an ethanolic solution of lithium acetate. The actual composition determined by ICP analysis was Li6.61La3Zr2Al0.13O11.98. Sintering these nanoparticles at 1100 C for 3 h in air after cold isostatic pressing brought a dense ceramic pellet with a relative density of 90.5%. The corresponding ionic conductivity with Au electrodes was 1.6 10 4 S cm 1 at room temperature. To study its electrochemical behavior as an electrolyte, a model cell of Li//(1 M LiPF6 + c-LLZO)//LiCoO2 configuration was constructed. Cyclic voltammetry of the cell delivered one set of redox couple with narrow voltage separation (15 mV) with a Li diffusion coefficient at room temperature of about 2 10 11 cm s 1 at the interface between LiCoO2 and 1 M LiPF6 + c-LLZO. The cell received an average discharge capacity of 64.4, 60.3, 56.1, 51.9 and 46.9 mA h cm 2 mm 1 at discharge rates 0.5C, 1C, 2C, 4C and 6C, respectively. The cell exhibited complete oxidation and reduction reactions with an average initial discharge capacity of about 64 mA h cm 2 mm , which is 92.7% of LiCoO2 theoretical value. These observations indicate the applicability of the present c-LLZO as an electrolyte for a solid-state Li-ion battery.

Far-from-equilibrium nanostructured ZnAl2O4 is prepared via simple and straightforward mechanochemical synthesis. Upon heating above 1100 K, mechanosynthesized ZnAl2O4 relaxes towards a structural state that is similar to the bulk one.

Institute of Nanotechnology, Kar Hermann-von-Helmholtz-Platz 1, 76344 Egg fabianm@saske.sk; vladimir.sepelak@kit.e 721-60828929 Institute of Geotechnics, Slovak Academy o Slovakia Institute for Chemistry and Technology of (NAWI Graz), Stremayrgasse 9, 8010 Graz, A Institute of Physics, Pavol Jozef Šafárik Uni Slovakia Institute of Physical Chemistry and Electro Callinstr., 3-3a, 30167 Hannover, Germany Center for Solid State Chemistry and N Hannover, Callinstr., 3-3a, 30167 Hannover Department of Physics, State University of Maringá, Brazil Cite this: RSC Adv., 2015, 5, 54321

Simple mixing or shaking of alkaline earth hydroxides with ammonium fluoride results in nanocrystalline phase pure metal fluorides MF2 (M: Ca, Sr, Ba). The formation of the alkaline earth fluorides was investigated by varying the reaction conditions. Evidence was found that just the contact between the starting materials is sufficient for the reaction to take place. X-ray diffraction, elemental analysis, 19F MAS NMR spectroscopy, and measurements of DC conductivities were used to characterize the fluorides regarding properties like crystal structure, crystallite sizes, local fluorine coordination, and fluorine ion conductivity. The 19F MAS NMR spectra of the phase pure fluorides prepared showed several signals, which were assigned to defects, impurities, or geometric distortions. The fluorides prepared by mixing or shaking revealed fluorine ion conductivities several orders of magnitude higher than observed for the respective microcrystalline alkaline earth fluorides. Therefore, the synthesis routine presented in this study may open a path to a very quick and simple synthesis of nanocrystalline fast fluorine ion conductors.

Technological and scientific challenges coupled with environmental considerations have prompted a search for simple and energy-efficient syntheses and processing routes of materials. This tutorial review provides an overview of recent research efforts in non-conventional reactions and syntheses of oxides induced by mechanical action. It starts with a brief account of the history of mechanochemistry. Ensuing discussions will review the progress in homogeneous and heterogeneous mechanochemical reactions in oxides of various structures. The review demonstrates that the event of mechanically induced reactions provides novel opportunities for the non-thermal manipulation of materials and for the tailoring of their properties.

Fluorine in polytetrafluoroethylene (PTFE) changes its states and transfers to titania by comilling and annealing of a titania-PTFE mixture. XPS, F-19 MAS NMR, FT-IR. Raman spectra, TEM and EDX analyses consistently indicated the oxidative decomposition of PTFE, inducing partial fluorination of titania. Incorporation of fluorine into titania was unambiguously confirmed by the appearance of a new XPS F1s peak at similar to 685 eV, similar to those observed from TiOF2. The intensity of the new F1s peak increased with comilling time and became a sole peak after milling for 3 h. At the same time, F-19 MAS NMR lines specific to PTFE disappeared. From these observations, we concluded that extensive decomposition of PTFE with simultaneous change in the chemical states of fluorine took place with the aid of titania. Upon annealing the comilled mixture in air, the amount of fluorine in the mixture decreased with increasing temperature, while the remaining fluorine migrated into the titania lattice, as confirmed by the decrease in the chemical shift of the F-19 MAS NMR lines and the decrease in the rutile (211) and (220) interplanar distances. These findings allow us to devise how to control the amount, states, and spatial distribution of the fluorine incorporated into titania.