The layered perovskite K2SrTa2O7: hydration and K+/H+ ion exchange

We present a full characterization of the anhydrous layered material K2SrTa 2O7 related to Ruddesden-Popper type phases. The unit cell, determined from powder X-ray diffraction, is tetragonal with a = 3.9858(1) Angstrom and c = 21.785(1) Angstrom (space group epsilon I4/mmm, Z = 2). The layered struc ture allows spontaneous water intercalation when the product is kept in air at ambient temperature. During hydration, a reversible structural transfor mation from an I to a P Bravais lattice is observed. By using K+/H+ ion exc hange, in dilute HNO3 or in acetic acid, we obtained the protonated phase H 2SrTa2O7. xH(2)O which is compared to the one synthesized from Li2SrTa2O7 p reviously reported by us. For both compounds, the hydration-dehydration beh avior, studied by DTA/TGA and X-ray thermodiffractometry is discussed. In a ddition, we carried out an electron microscopy study of anhydrous K2SrTa2O7 by selected area electron diffraction (SAED).