The Synthesis of Ba‐ and Fe‐ Substituted CsAlSi2O6 Pollucites

Barium‐substituted CsAlSi₂O₆ pollucites, Cs_xBa_(1?x)/2AlSi₂O₆, and barium‐ and iron‐substituted pollucites, Cs_xBa_(1?x)/2Al_xFe_1?xSi₂O₆ and Cs_xBa_1?xAl_xFe_1?xSi₂O₆ were synthesized with 1 ≥ x≥ 0.7 using a hydrothermal synthesis procedure. Rietveld analysis of X‐ray diffraction data confirmed the substitution of Ba for Cs and Fe for Al, respectively. The crystallographic analysis also describes the effects of three different types of pollucite substitutions on the pollucite unit cell: Ba²⁺ for Cs¹⁺ cation results in little effect on cell dimensions, intermediate concentrations of Ba²⁺ and Fe³⁺ substitution result in net minor expansion due to Fe³⁺ addition, and large Ba and Fe substitutions result in overall framework contraction. Elemental analysis combined with microscopy further supports the phase purity of these new phases. These materials can be used to study the stability of CsAlSi₂O₆ as a durable ceramic waste form, which could accommodate with time Cs and its decay product, Ba. Furthermore, success in iron substitution for aluminum into the pollucite lattice predicts that redox charge compensation for Cs cation decay is possible.