Influence of synthesis methodology on the ionic transport properties of BaSnF4

Epp

Nakhal

et al. 2014

Phys. Status Solidi C

Fast ion conductors play one of the most important roles in solid state ionics as there is a great demand for their application in safe and powerful electrochemical energy storage systems. For such materials, it is known that the synthesis conditions may have significant impact on the final properties of the materials prepared. In this contribution, we made use of mechanosynthesis, carried out via high‐energy ball milling, to influence the ionic transport parameters of tetragonal, i.e., layer‐structured, BaSnF4. X‐ray powder diffraction (XRD) revealed that mechanical treatment of the binary fluorides BaF2 and SnF2 leads to a powder pointing to a nanocrystalline fluoride with (distorted) cubic symmetry. Differential scanning calorimetry (DSC) as well as preliminary in situ XRD measurements were used to follow the transformation towards the tetragonal modification with the composition BaSnF4. Broadband impedance spectroscopy was used to measure the overall electrical conductivity of the ternary fluoride. Remarkably, the layered form shows a room temperature conductivity of 7 × 10–4 S cm–1. Further emphasis was put on the characterization of the dielectric properties of the material, which was investigated by using different electrode materials to distinguish artefacts from intrinsic properties. Since we found a strong dependence of the real part of the permittivity on the electrode materials applied (carbon paste or sputtered Pt), we tend to assign the huge increase in permittivity, which was recently interpreted as giant dielectric constant, to interfacial polarization effects rather than to intrinsic properties. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Section: Impedance Spectroscopymentioning

confidence: 77%

Defect‐enhanced F^– ion conductivity in layer‐structured nanocrystalline BaSnF₄ prepared by high‐energy ball milling combined with soft annealing

Epp

Nakhal

et al. 2014

Phys. Status Solidi C

“…Cation ordering is caused by the steric demand of the unpaired electrons of the Sn atoms. 39,40 PbSnF 4 and BaSnF 4 can be prepared by means of solid state synthesis at high temperatures; [41][42][43] alternatively, the ternary fluorides can be synthesized by mechanochemical means as well. [43][44][45][46] In the case of BaSnF 4 , the highest conductivity was reached if a mechanochemical milling route was chosen.…”

Section: Applications In Electrochemical Energy Storagementioning

confidence: 99%

“…39,40 PbSnF 4 and BaSnF 4 can be prepared by means of solid state synthesis at high temperatures; [41][42][43] alternatively, the ternary fluorides can be synthesized by mechanochemical means as well. [43][44][45][46] In the case of BaSnF 4 , the highest conductivity was reached if a mechanochemical milling route was chosen. 43,46 The same holds for SnF 2 : if treated in a high-energy ball its conductivity can be increased by almost two orders of magnitude.…”

Section: Applications In Electrochemical Energy Storagementioning

confidence: 99%

“…[43][44][45][46] In the case of BaSnF 4 , the highest conductivity was reached if a mechanochemical milling route was chosen. 43,46 The same holds for SnF 2 : if treated in a high-energy ball its conductivity can be increased by almost two orders of magnitude. 47 Unfortunately, SnF 2 -based fluorides are highly reactive, i.e., unstable under electrochemical conditions complicating practical applications.…”

Section: Applications In Electrochemical Energy Storagementioning

confidence: 99%

See 1 more Smart Citation

Mechanochemically synthesized fluorides: local structures and ion transport

Wilkening

2016

Dalton Trans.

The performance of new sensors or advanced electrochemical energy storage devices strongly depends on the active materials chosen to realize such systems. In particular, their morphology may greatly influence their overall macroscopic properties. Frequently, limitations in classical ways of chemical preparation routes hamper the development of materials with tailored properties. Fortunately, such hurdles can be overcome by mechanochemical synthesis. The versatility of mechanosynthesis allows the provision of compounds that are not available through common synthesis routes. The mechanical treatment of two or three starting materials in high-energy ball mills enables the synthesis not only of new compounds but also of nanocrystalline materials with unusual properties such as enhanced ion dynamics. Fast ion transport is of crucial importance in electrochemical energy storage. It is worth noting that mechanosynthesis also provides access to metastable phases that cannot be synthesized by conventional solid state synthesis. Ceramic synthesis routes often yield the thermally, i.e., thermodynamically, stable products rather than metastable compounds. In this perspective we report the mechanochemical synthesis of nanocrystalline fluorine ion conductors that serve as model substances to understand the relationship between local structures and ion dynamics. While ion transport properties were complementarily probed via conductivity spectroscopy and nuclear magnetic relaxation, local structures of the phases prepared were investigated by high-resolution (19)F NMR spectroscopy carried out by fast magic angle spinning. The combination of nuclear and non-nuclear techniques also helped us to shed light on the mechanisms controlling mechanochemical reactions in general.

“…The conductivity of the tetragonal modification of BaSnF 4 is much higher than that of the "cubic" form (see Figure 15c). BaSnF 4 is, besides PbSnF 4 [55], known to be one of the fastest F anion conductors (Figure 16) [55,[63][64][65]. Similar to BaMgF 4 , it shows anisotropic conduction characteristics.…”

Section: F Mas Nmrmentioning

confidence: 99%

Structure and ion dynamics of mechanosynthesized oxides and fluorides

Wilkening

Düvel

Zeitschrift Für Kristallographie - Crystalline Materials

et al. 2016

Abstract: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.