New n = 3 Dion-Jacobson phases NaLn2Ti2NbO10·xH2O (Ln = La, Pr, Nd, Sm)

The n = 3 Dion-Jacobson phases, NaLn2Ti2NbO10·xH2O (Ln = La, Pr, Nd, Sm), have been prepared by the ion-exchange reaction of CsLn2Ti2NbO10. Their crystal structures were determined by the Rietveld analysis of powder X-ray diffraction patterns, and they were found to keep the new-type ordering sequence of (Ti1/2Nb1/2)O6-TiO6-(Ti1/2Nb1/2)O6 in the tripled BO6 octahedra. The interlayer Na cations and H2O molecules were proposed for the first time to be situated at the 8g and 4e sites in the space group I4/mmm, forming face-shared octahedra along the (110) direction. Upon firing, they were dehydrated into new intermediate hydrates with P4/mmm symmetry at around 100 oC, and then NaLn2Ti2NbO10 with I4/mmm symmetry at above 200 oC.