Electron-irradiation induced phase transformation in La1/3Zr2(PO4)3: La3+ displacement in a preserved NASICON framework

The La1/3Zr2(PO4)3 NASICON-type compound (S.G. P3¯ - neutron and X-ray diffraction experiments) is investigated by transmission electron microscopy (TEM) technique, selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM), in order to study locally the lanthanum distribution. An irreversible structural transformation (P‐‐‐→P‐c‐→R‐‐‐) is observed, without modification of the atomic content and cell size, as soon as the phase is illuminated by the electron beam. The progressive disappearance of the spots which do not check the R conditions on the SAED patterns is clearly shown along two zone axis, [001] and [100]. This transformation implies the displacement of the two La3+ cations in a preserved classical [Zr2(PO4)3]− network. This interesting behavior is in good agreement with the La3+ ionic conductivity observed in La1/3Zr2(PO4)3 (4.09×10−7 S cm−1 at 700 °C). To our knowledge, this is the first time that a complete TEM study is done on a NASICON-type phase.

Diffraction pattern of a crystallite of La1/3Zr2(PO4)3 showing the transformation under the electron beam (a) at the beginning and (b) at the end.Figure optionsDownload as PowerPoint slide