Insights into Formation Conditions, Crystal Structures, and Thermal Behavior of Hydrous and Anhydrous Barium Arsenates

Abstract

During systematic phase formation studies in the system BaO/As2O5/H2O, the phases with composition Ba3(AsO4)2·16.3H2O, Ba3(AsO4)2·17H2O, Ba(H2AsO4)2·H2O, Ba(H2AsO4)2, Ba3(HAs2O7)2, Ba3As4O13, Ba2As2O7, and Ba2As4O12 were isolated and structurally characterized for the first time, using either X-ray powder diffraction data (Ba3As4O13) or single crystal X-ray diffraction data (all other phases). From the eight phases investigated, three (Ba(H2AsO4)2, Ba3As4O13, and Ba2As2O7) crystallize in known structure types and the remaining ones in novel structure types. In the crystal structures, the coordination numbers of the Ba2+ cations span a range from 8 to 11, and the different arsenate anions are built up from tetrahedral AsO4 groups, except for Ba2As4O12 that contains a novel type of a catena-metaarsenate anion consisting of condensed AsO4 tetrahedra and AsO6 octahedra. Another remarkable structural feature is the hydrogendiarsenate anion present in Ba3(HAs2O7)2, with the longest As–Obridging distance of a di...