Abstract
We present a full structural characterisation by powder diffraction of K2Sr1.5Ta3O10 and K2Sr1.5Ta3O10·H2O, the structures of which are related to that of the Ruddlesden–Popper n = 3 member layered perovskite phases (K2Sr1.5Ta3O10, I4/mmm, a = 3.9626(1) Å, c = 30.3257(7) Å, Z = 2; K2Sr1.5Ta3O10·H2O, P4/mmm, a = 3.9499(2) Å, c = 17.031(3) Å, Z = 1). We show that K2Sr1.5Ta3O10
can be synthesized either directly from conventional procedures or by controlling the continuous thermal decomposition of K2SrTa2O7
(n = 2 member) following the scheme: K2SrTa2O7 → 2/3 K2Sr1.5Ta3O10 + 1/3 K2O. K2Sr1.5Ta3O10 undergoes a fast and reversible hydration process studied by DTA/TGA experiments. In both the anhydrous and mono-hydrated phases, most of the K+ ions are located in the interlayer between the perovskite slabs constituted by a stacking of three TaO6 octahedra. The remainder of the K+ ions, all the Sr2+ ions and vacancies are distributed on the twelve coordinated A sites of the perovskite blocks. In the case of K2Sr1.5Ta3O10·H2O,
the