pyrochlore by synchrotron X-ray techniques*

Ordering and disordering mechanism has a substantial effect on the physicochemical properties of complex oxides when they are exposed to harsh conditions like high pressure or ion irradiation. In this work, swift heavy ion (100 MeV I⁷⁺) irradiation-induced pyrochlore to defect fluorite phase transformation with amorphous fraction in Nd₂Zr₂O₇ has been investigated. XRD results indicate that the Nd₂Zr₂O₇ is transformed to a defect fluorite phase with an amorphous fraction on irradiation at the highest fluence of 5×10¹³ ions/cm². By examining the XANES and EXAFS spectra of irradiated materials, it was possible to analyze how the local coordination environment around the absorbing atoms changed at various fluences. The change in the intensities of main edge features and shifting in the energy position of Zr K-edge XANES spectra with ion fluences are also good indicators of the phase transition from pyrochlore to defect fluorite structure, which is supported by the FT modulus of Zr K-edge and Nd L₃ - edge. In-situ thermal annealing investigation was performed in the temperature range of 300 to 1000 ᵒC on pristine and irradiated Nd₂Zr₂O₇ pyrochlore at 5×10¹³ ions/cm² using synchrotron x-ray diffraction. The behavior of isochronal annealing is described in terms of improved defect recovery, which demonstrates that pyrochlore superstructure does not appear even at a high temperature of 1000 ^ᵒC.