Rare-Earth Zirconate Ln₂Zr₂O₇ (Ln: La, Nd, Gd, and Dy) Powders, Xerogels, and Aerogels: Preparation, Structure, and Properties

The physicochemical properties of rare-earth zirconates can be tuned by the rational modification of their structures and phase compositions. In the present work, La 3+ -, Nd 3+ -, Gd 3+ -, and Dy 3+ -zirconate nanostructured materials were prepared by different synthetic protocols, leading to powders, xerogels, and, for the first time, monolithic aerogels. Powders were synthesized by the co-precipitation method, while xerogels and aerogels were synthesized by the sol–gel technique, followed by ambient and supercritical drying, respectively. Their microstructures, thermogravimetric profiles, textural properties, and crystallographic structures are reported. The co-precipitation method led to dense powders ( S BET < 1 m 2 g –1 ), while the sol–gel technique resulted in large surface area xerogels ( S BET = 144 m 2 g –1 ) and aerogels ( S BET = 168 m 2 g –1 ). In addition, the incorporation of lanthanide ions into the zirconia lattice altered the crystal structures of the powders, xerogels, and aerogels. Single-phase pyrochlores were obtained for La 2 Zr 2 O 7 and Nd 2 Zr 2 O 7 powders and xerogels, while defect fluorite structures formed in the case of Gd 2 Zr 2 O 7 and Dy 2 Zr 2 O 7 . All aerogels contain a mixture of cubic and tetragonal ZrO 2 phases. Thus, a direct effect is shown between the drying conditions and the resulting crystalline phases of the nanostructured rare-earth zirconates.