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, La³⁺-, Nd³⁺-, Gd³⁺-, and Dy³⁺-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 m² g^-1), while the sol-gel technique resulted in large surface area xerogels (S_BET = 144 m² g^-1) and aerogels (S_BET = 168 m² 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 La₂Zr₂O₇ and Nd₂Zr₂O₇ powders and xerogels, while defect fluorite structures formed in the case of Gd₂Zr₂O₇ and Dy₂Zr₂O₇. All aerogels contain a mixture of cubic and tetragonal ZrO₂ phases. Thus, a direct effect is shown between the drying conditions and the resulting crystalline phases of the nanostructured rare-earth zirconates.