Abstract

We present a full structural characterisation by powder diffraction of K₂Sr_1.5Ta₃O₁₀ and K₂Sr_1.5Ta₃O₁₀·H₂O, the structures of which are related to that of the Ruddlesden–Popper n = 3 member layered perovskite phases (K₂Sr_1.5Ta₃O₁₀, I4/mmm, a = 3.9626(1) Å, c = 30.3257(7) Å, Z = 2; K₂Sr_1.5Ta₃O₁₀·H₂O, P4/mmm, a = 3.9499(2) Å, c = 17.031(3) Å, Z = 1). We show that K₂Sr_1.5Ta₃O₁₀ 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 K₂Sr_1.5Ta₃O₁₀ + 1/3 K₂O. K₂Sr_1.5Ta₃O₁₀ 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 K₂Sr_1.5Ta₃O₁₀·H₂O, the water molecules are found in the interlayer on the (002) plane.