Temperature-dependent structural evolution and stability of divalent anion bearing alumosilicate cancrinites

Abstract

Abstract A comprehensive study of XO42--cancrinites with X = Mn, Cr, Se, Mo and W was carried out, focusing on the effect of incorporated anions on the framework structure. At room temperature an anisotropic unit cell expansion with increasing anion size was observed. The size of the incorporated anions has no influence on the framework angles or the channel radii. In temperature-dependent (TD) studies four different regimes could be identified: first a quasi-linear expansion of the cancrinites containing water molecules in the e -cages; second, the dehydration process; third the quasi-linear expansion regime of the dehydrated phase to a maximum expanded structure, followed by a phase transformation or decomposition (fourth). The temperature at which the maximum expanded structure is reached, decreases with increasing size of the incorporated anion. Further, it is shown, that thermally stable anions can promote a reconstructive phase transformation to the corresponding cubic nosean-type structure. The absence of an amorphous intermediate state as well as the complete ordering of the template ions indicate a fast transformation mechanism based on the translation of six-ring layers from a hexagonal ABAB to a cubic ABCABC staking.