Minerals to Functional Materials: Characterization of Structural Phase Transitions and Raman Analysis of a Superionic Phase in Na6Co(So(4))(4)

摘要

In search of promising Na+ ion conductors, we have detected a superionic phase in a Vantoffite mineral, Na6Co(SO4)(4), at 570 degrees C, thus enhancing the use of minerals to produce futuristic solid state electrolytes. Na6Co(SO4)(4) crystallizes concomitantly to produce di- and tetrahydrate forms from an aqueous solution. Both the crystal forms belong to a triclinic system, space group P (1) over bar. The mineral transforms to a dehydrated phase as established by in situ single crystal X-ray diffraction at 217 degrees C and is shown to be isostructural with its Mn analogue. Even though thermal analysis indicates a single structural phase transition at 450 degrees C, the features associated with in situ powder X-ray diffraction as well as in situ Raman spectroscopy signify a second phase transition approximate to 540 degrees C and the behavior of ionic conductivity leads to a superionic phase (sigma approximate to 10(-2) S/cm at 570 degrees C). These observations are significant for the development and understanding of mineral based solid electrolytes.