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) and hydrated HLaTiO4 . H2O were synthesized by Na+/H+ exchange of NaLnTiO(4) in 0.1 N HNO3 solutions. This protonated oxide retains the parent layered structure (P4/nmm), the layers being separated by H+ ions occupying nine-coordinated Na+ sites and adjacent blocks having the staggered conformation. Due to the relative displacements of proton layers on hydration, on the contrary, a doubling of c axis was observed in hydrated type HLaTiO4 . H2O (x similar to 0.4). Thermal behaviors examined by thermogravimetric analyses showed that the interlayer protons are lost below 600 degrees C as water. Further heating above the dehydration temperature led to LnTiO(3.5) which still contained perovskite layers. They transformed into corresponding pyrochlores Ln(2)Ti(2)O(7) from around 950 degrees C. (C) 1996 Academic Press, Inc.