Abstract
Nanostructured materials have already become an integral part of our daily life. In many applications, ion mobility decisively affects the performance of, e.g., batteries and sensors. Nanocrystalline ceramics often exhibit enhanced transport properties due to their heterogeneous structure showing crystalline (defect-rich) grains and disordered interfacial regions. In particular, anion conductivity in nonstructural binary fluorides easily exceeds that of their coarse-grained counterparts. To further increase ion dynamics, aliovalent substitution is a practical method to influence the number of (i) defect sites and (ii) the charge carrier density. Here, we used high energy-ball milling to incorporate Y 3 + ions into the cubic structure of SrF 2 . As compared to pure nanocrystalline SrF 2 the ionic conductivity of Sr 1 − x Y x F 2 + x with x = 0.3 increased by 4 orders of magnitude reaching 0.8 × 10 − 5 S cm − 1 at 450 K. We discuss the effect of YF 3 incorporation on conductivities isotherms determined by both activation energies and Arrhenius pre-factors. The enhancement seen is explained by size mismatch of the cations involved, which are forced to form a cubic crystal structure with extra F anions if x is kept smaller than 0.5.
Highlights
Nanostructured materials assume a variety of functions in quite different applications and devices of our daily life [1]
For nano-engineered systems, which were prepared by bottom-up procedures, such as gas condensation or epitaxial methods [20,21], space charge regions lead to non-trivial effects that may enhance ion transport
High-energy ball milling is able to force the distinctly sized cations to form a mixed phase with structural disorder at atomic scale
Summary
Nanostructured materials assume a variety of functions in quite different applications and devices of our daily life [1]. If prepared via a top-down approach such as ball milling [8,23,24,25], the nanocrystalline material obtained is anticipated to consist of nm-sized crystals surrounded by structurally disordered regions [6,26]. This structural model helped rationalize ion dynamics in oxides [8]. Metastable Ba1− x Cax F2 , cannot be prepared via solid state synthesis; instead, it is only accessible by high-energy ball milling that forces the cations ions, substantially differing in size, to form a solid solution at atomic scale [12]. As pointed out by Ritter et al nanoscopic compounds based on SrF2 as host for rare elements might act as new luminescent materials [36]
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