Probing local structure of pyrochlore lead zinc niobate with synchrotron x-ray absorption spectroscopy technique

Abstract

Local structure of lead zinc niobate (PZN) ceramic, synthesized via B-site oxide precursor route in atmospheric pressure, was investigated using synchrotron x-ray absorption spectroscopy (XAS) technique. The x-ray absorption near-edge structure (XANES) simulation was first carried out. The XANES simulation results indicate that the PZN ceramic is in pyrochlore phase having Zn2+substituted on Nb5+site. Afterwards, the extended x-ray absorption fine structure (EXAFS) analysis was performed to extract the bond length information between Zn2+and its neighboring atoms. From the EXAFS fitting, the bond length between Zn2+and Pb2+in the pyrochlore phase was found to be longer than the previously reported bond length in the perovskite phase. Further, with the radial distribution information of Zn2+'s neighboring atoms, the formation energies along the precursor-to-pyrochlore and precursor-to-perovskite reaction paths were calculated using the density functional theory (DFT). The calculated results show that the formation energy of the perovskite phase is noticeably higher than that of the pyrochlore phase, which is influenced by the presence of energetic Pb2+lone pair, as the perovskite phase has shorter Zn2+to Pb2+bonding. This therefore suggests the steric hindrance of Pb2+lone pair and the mutual interactions between Pb2+lone pair and Zn2+are main causes of the instability of lead zinc niobate in the perovskite structure and confirm the efficacy of XAS and DFT analysis in revealing local structural details of complex pyrochlore materials. © 2013 AIP Publishing LLC.