Abstract: Hydrothermally synthesized ReNaTi₂O₆(Re=Ce, Nd and Eu) were characterized by means of XRD, SEM, XPS and ¹⁵¹Eu Mossbauer
spectroscopy. The results show that the crystallization conditions e.g., the mineralizer, initial molar concentration and so on determine the structural
types and the purity of the resulting products. During the hydrothermal crystallization, sodium ions may occupy the perovskite lattice but do not result in the reduction
of Ti(IV) to lower valence state. The binding energy for the main peak of Ce3d_5/2 in CeNaTi₂O₆ is 885.45eV, suggesting that the cerium ions exist mainly as Ce(III). NdNaTi₂O₆ has regular grain shape. For EuNaTi₂O₆,
the contribution from the lattice field is larger than that of second 4f. The products from hydrothermal conditions have lower defect concentration and smaller
lattice distortion.

Key words: hydrothermal route, double peroskite, Mossbauer spectra