Synthesis, characterization and dehydration study of H2A0.5nBnO3n+1•xH2O (n=2 and 3, A = Ca, Sr and B=Nb, Ta) compounds obtained by ion-exchange from the layered Li2A0.5nBnO3n+1 perovskite materials

We have synthesized several new layered protonated materials related to Ruddlesden-Popper phases, H(2)A(0.5n)B(n)O(3n+1). xH(2)O (A = Ca, Sr; B = Nb, Ta), by ion-exchange of the lithium ion from Li(2)A(0.5n)B(n)O(3n+1), a family of layered perovskites recently synthesized by us, in dilute HNO3 at 60 degrees C. The protonated derivatives show interesting dehydration properties with formation of layered anhydrous phases followed by a transformation to novel metastable A(0.5)BO(3) compounds. The latter oxides, irrespective of the n-value of the mother phase, transform on further heating to the thermodynamically stable AB(2)O(6) materials. The structural transformations occurring during the dehydration process are characterized by X-ray powder diffraction and electron microscopy techniques.