Fluorine Translational Anion Dynamics in Nanocrystalline Ceramics: SrF2-YF3 Solid Solutions

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.

Ceramic Conductors

“…Oxygen ions are mobile charge carriers in materials such as substituted bismuth vanadate [4] and doped cerium oxide [5,6], as studied by Ring and Fuierer, and to a minor extent and at high temperature, they are also mobile charge carriers in ceramic proton conductors. Fluorine ions, the first mobile ions studied in solid-state ionic conductors, are present in SrF 2 -YF 3 solid solutions, as reported by Breuer et al [7]. Finally, electronic-type charge carriers dominate in such ceramics as donor-doped and reduced strontium titanate, as reported by Presto and collaborators [8].…”

“…On the other hand, the application of mechanosynthesis not only produces nanoceramic powder but also facilitates the formation of phases which do not form with the use of other methods. By employing mechanosynthesis, a single-phase solid solution of YF 3 and SrF 2 was obtained before the Sr 0.7 Y 0.3 F 2.3 composition [7].…”

“…Similarly, the development of proton-conducting ceramics [2,3] is aimed at future applications in SOFCs with proton-conducting electrolytes. SOFCs both with oxygen ionand proton-conducting electrolytes operate at high temperatures, i.e., between 600 • C and 800 • C. Even the YF 3 -SrF 2 solid solutions are considered as electrolytes for high-temperature all-solid-state fluorine batteries [7]. Electro-ceramic devices like solid oxide fuel cells, electrolysers, and batteries are multi-layered systems consisting of different materials.…”

Mechanochemistry of fluoride solids: from mechanical activation to mechanically stimulated synthesis

“…Furthermore, the successful mechanochemical synthesis of the following complex fluorides has been reported: BaMgF 4 [37,38], SrMgF 4 [39], BaSnF 4 [40] RbSn 2 F 5 [41], NaSn 2 F 5 [42], KSn 2 F 5 [43] and Li 3 AlF 6 [44]. Moreover, the mechanochemical synthesis was successful for solid solutions of (i) alkaline earth metal fluorides or PbF 2 with cubic symmetry M I 1−x M II x F 2 (M: Ca, Sr, Ba, Pb) (fluorite structure) [45][46][47][48][49], of (ii) alkaline earth metal fluorides with rare earth fluorides or YF 3 [50][51][52][53][54] or of (iii) SnF 2 with alkaline metal fluorides [55, . The authors were able to show that the mechanochemical route, partially combined with thermal post-treatment, is a simple synthesis method for nanocrystalline fluoride solids [57,58].…”

Ангармонизм колебаний решетки и тепловые свойства твердых растворов Сd-=SUB=-1-x-=/SUB=-Sr-=SUB=-x-=/SUB=-F-=SUB=-2-=/SUB=-

“…Фториды щелочно-и редкоземельных элементов, а также их взаимные изо-и гетеровалентные твердые растворы находят все более широкое применение в различных областях современной оптоэлектроники [1][2][3][4][5][6]. Привлекательность практического использования твердых растворов обусловлена возможностью плавно изменять свойства раствора, изменяя содержание в нем компонентов.…”