Relationship between crystal structure and oxide-ion conduction in Ln2Zr2O7 (Ln = Eu, Nd and La) system deduced by neutron and X-ray diffraction

摘要

Crystal structures of the Ln ₂Zr₂O₇ ( Ln = Nd and La) were refined by the Rietveld analysis of powder neutron diffraction (ND) data at room temperature. La₂Zr₂O₇ had a pyrochlore (P)-type structure of almost completely ordered for oxygen vacancy. On the other hand, Nd₂Zr₂O₇ had the P-type structure for the oxygen vacancy distributed between the O2 (8 b ) and O3 (48 f ) sites. The Rietveld refinement results of powder X-ray diffraction (XRD) data of Ln ₂Zr₂O₇ ( Ln = Eu, Nd and La) indicated that the Ln 3+ and Zr4+ ions exist in ordered states in 16 c and 16 d sites, respectively. The refined lattice parameters ( a ), occupancies ( g ) for oxygen sites (O1, O2 and O3) and x -positional parameters for O3 (48 f ) site of La₂Zr₂O₇ and Nd₂Zr₂O₇ by using powder XRD data were in almost agreement with those by using powder ND data. The refined ND and XRD data of Ln ₂Zr₂O₇ ( Ln = Eu, Nd and La) system revealed that the O3 (48 f ) site occupancy ( g _{48 f} ) decreases with increasing O2 (8 b ) site occupancy, while O1 (8 a ) site occupancy keeping 1.0. The change in oxide-ion conductivity (σ) in Ln ₂Zr₂O₇ ( Ln = Eu, Nd and La) system can be related to a change in the product of site occupancy ( g _{48 f} ) and the oxygen vacancy rate (1- g _{48 f} ) in the O3 (48 f ) site, g _{48 f} (1- g _{48 f} ).