A NEW FAMILY OF PROTONATED OXIDES HLNTIO(4) (LN=LA, ND, SM, AND GD)

A new series of well crystallized HLnTiO(4) (Ln=La, Nd, Sm, and Gd) an d hydrated HLaTiO4 . H2O were synthesized by Na+/H+ exchange of NaLnTi O(4) in 0.1 N HNO3 solutions. This protonated oxide retains the parent layered structure (P4/nmm), the layers being separated by H+ ions occ upying nine-coordinated Na+ sites and adjacent blocks having the stagg ered conformation. Due to the relative displacements of proton layers on hydration, on the contrary, a doubling of c axis was observed in hy drated type HLaTiO4 . H2O (x similar to 0.4). Thermal behaviors examin ed by thermogravimetric analyses showed that the interlayer protons ar e lost below 600 degrees C as water. Further heating above the dehydra tion temperature led to LnTiO(3.5) which still contained perovskite la yers. They transformed into corresponding pyrochlores Ln(2)Ti(2)O(7) f rom around 950 degrees C. (C) 1996 Academic Press, Inc.