Order-disorder structural transition of Nd2(Zr1-xCex)2O7 pyrochlores prepared by auto-combustion method

A series of pyrochlore solid solutions with general formula Nd2(Zr1-xCex)2O7 were successfully synthesized by the glycine-nitrate process (GNP) auto-combustion method and then sintered at high temperature. The order -disorder structure of the as-prepared ceramic samples was systematically characterized by X-ray diffraction (XRD) and Raman spectroscopy. Rietveld refinements of the typical XRD patterns were performed using Full-prof software. XRD and Raman results confirmed a co-existence structure composed of ordered pyrochlore and disordered defect-fluorite structure for Nd2(Zr0.75Ce0.25)2O7 and Nd2(Zr0.7Ce0.3)2O7 samples. And Nd2Ce2O7 specimen presented as defect-fluorite structure with rare earth C-type microdomains in both XRD and Raman spectroscopy. The effect of 48f oxygen on phase transition was verified by XRD and Raman spectroscopy. The refined x-parameter of 48f oxygen reflected the phase transition of Nd2(Zr1-xCex)2O7 solutions from pyrochlore to fluorite structure. High resolution transmission electron microscope (HRTEM) images and selected area electron diffraction (SAED) analysis of transmission electron microscopy (TEM) proved the representative Nd2(Zr0.7Ce0.3)2O7 sample showed biphasic structure with pyrochlore and defect-fluorite structure SAED rings. Also, the C-type microdomain SAED rings of Nd2Ce2O7 structure was found by TEM analysis.