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

We present a full characterization of the anhydrous layered material K2SrTa2O7 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 structure allows spontaneous water intercalation when the product is kept in air at ambient temperature. During hydration, a reversible structural transformation from an I to a P Bravais lattice is observed. By using K+/H+ ion exchange, in dilute HNO3 or in acetic acid, we obtained the protonated phase H2SrTa2O7. xH(2)O which is compared to the one synthesized from Li2SrTa2O7 previously reported by us. For both compounds, the hydration-dehydration behavior, studied by DTA/TGA and X-ray thermodiffractometry is discussed. In addition, we carried out an electron microscopy study of anhydrous K2SrTa2O7 by selected area electron diffraction (SAED).