Abstract

We have synthesized several new layered protonated materials related to Ruddlesden–Popper phases, H₂A_0.5nB_nO_{3n + 1}·xH₂O (A = Ca, Sr; B = Nb, Ta), by ion-exchange of the lithium ion from Li₂A_0.5nB_nO_{3n + 1}, a family of layered perovskites recently synthesized by us, in dilute HNO₃ at 60 °C. The protonated derivatives show interesting dehydration properties with formation of layered anhydrous phases followed by a transformation to novel metastable A_0.5BO₃ compounds. The latter oxides, irrespective of the n-value of the mother phase, transform on further heating to the thermodynamically stable AB₂O₆ materials. The structural transformations occurring during the dehydration process are characterized by X-ray powder diffraction and electron microscopy techniques.