Synthesis, characterization and dehydration study of H(2)A(0.5n)B(n)O(3n+1)center dot xH(2)O (n=2 and 3, A = Ca, Sr and B=Nb, Ta) compounds obtained by ion-exchange from the layered Li(2)A(0.5n)B(n)O(3n+1) perovskite materials

We have synthesized several new layered protonated materials related to Rud dlesden-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 fam ily of layered perovskites recently synthesized by us, in dilute HNO3 at 60 degrees C. The protonated derivatives show interesting dehydration propert ies 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 th ermodynamically 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.