REACTIVITY OF THE INTERLAYER SPACE OF THE NEW ALKALINE INSERTED NIOBOFERRITES K(RB)NB1.5FE0.5O5 - ALKALINE DEFECTS AND ACIDIC EXCHANGE

KNb1.5Fe0.5O5 and RbNb1.5Fe0.5O5 are two new nioboferrites isotypic wi th the titanoniobate KTiNbO5. They are prepared by solid state reactio n at 1100 degrees C. (XRD) analysis points to an orthorhombic unit cel l : a # 6.5 Angstrom; b # 3.8 Angstrom; c # 18.5 Angstrom (K), 19.1 An gstrom (Rb). The alkaline cations inserted in the interlayer space are highly reactive. They can be partly removed when a Fe(III) --> Nb(V) substitution is operated in the octahedral layers. The larger homogene ity range of the K-1-x(Nb-1.5+(x/2)Fe-0.5-(x/2))O-5 series (x less tha n or equal to 0.30) evidences a significant ability to get K vacancies as compared to the Rb-1-x(Nb-1.5+(x/2)Fe-0.5-(x/2))O-5 series (x less than or equal to 0.10). The acidic exchange of K cations results in t he synthesis of the hydrated protonic oxide H(H2O)(x)Nb1.5Fe0.5O5 whos e dehydration at 130 degrees C is followed by a reconstructive decompo sition in a new Nb(V) and Fe(III) mixed oxide, which occurs at 300 deg rees C.