Evolution of Fluorite to Pyrochlore Transformation in Chemically Precipitated nano- Nd₂Zr₂O

Nanocrystalline Nd₂Zr₂O₇ was prepared by the coprecipitation method using zirconium oxalate as a precursor and subsequently calcined at temperatures between 500 and 1500 °C. The powders were characterized using X-ray diffraction (XRD), TGA-DTA, Raman spectroscopy, and SEM to evaluate their particle size and crystal structure. The crystallite size, estimated from the most intense XRD peak using the Scherrer equation, ranged from 17 to 76 nm. Upon heat treatment, the amorphous precursor crystallized into a defect fluorite structure at approximately 800 °C. With further increase in temperature (≥ 1000 °C), the defect fluorite phase gradually transformed into the pyrochlore phase accompanied by a decrease in the 48f oxygen positional parameter. Combined Rietveld refinement and Raman spectroscopy reveal the onset of anion ordering at 1000 °C, even in the absence of XRD-detectable superlattice reflections. The cation ordering increased from approximately 60% at 1100 °C to complete (100%) ordering at 1500 °C.