Structural complexity in AA 'MM'O6 Perovskites. A Transmission Electron Microscopy Study

摘要

We have prepared five perovskite compounds which have two different A-site cations and examined the ordering of the A-site lattice through powder X-ray diffraction, TEM, HRTEM, HAADF-STEM, STEM-EELS. NaLaTi2O6 and NaLaZr2O6 show no indication of cation ordering by XRD but TEM analysis reveals that the A-site cations are ordered into layers in nanometer domains which have perpendicular orientations of the layers. NaLaMgTe06 has larger domains which can be detected by XRD. XRD has revealed that both NaLaMgWOe and KLaMnWO6 have nearly complete long range layered ordering of the A-site cations. TEM microscopy has further shown that a compositional modulation exists in both compounds. NaLaMgWOe organizes into alternating stripes ~24A wide that are compositionally distinct from each other. KLaMnWO6 shows similar behaviour except with a chessboard pattern.