Structural optical and electrical properties of RE4Zr3O12 (RE = Dy, Y, Er, and Yb) nanoceramics

Concentration of oxide ion vacancies and its ordering in crystalline lattices play an important role in the structural, optical and ionic transport properties of RE2O3–MO2 (RE (Rare earths), M = Ti, Zr, Hf) systems. Rarely investigated rare earth zirconate system, RE4Zr3O12 (RE = Dy, Y, Er, and Yb) exhibiting the polymorphic structural forms, was chosen for the present study. RE4Zr3O12 nanoceramics were prepared through an auto-ignited combustion method; thereafter, dense bulk ceramics were derived from them at relatively low temperatures. X-ray diffraction studies carried out on the nanoceramics as well as bulk ceramics suggest defect fluorite structure for RE = Dy, Y and Er whereas δ-phase rhombohedral structure for RE = Yb ceramics. Extent of oxide ion ordering and the structural variations due to the replacement of rare earth ions in the crystalline lattices were analyzed by Raman and infrared spectroscopy. UV–Visible and photoluminescence spectroscopy were employed to investigate the optical properties of the nanoceramics. Impedance spectroscopic studies carried out on the bulk ceramic materials show that the oxide ion hopping conduction mechanism in the bulk ceramics was affected by the structural factors and free mobile oxide ion concentration. Increase of total electrical conductivity of the dense ceramics with the increase of temperature was in accordance with the Arrhenius relation. Electrical conductivity of fluorites was higher than the δ-phase ceramics, which was attributed to the decreased activation energy and increased available number of mobile oxide ions in the fluorite structure.