Elektronenmikroskopische Untersuchungen zur Realstruktur von La2CeTaO6Cl3 und dessen thermischem Abbauprodukt La2CeCe TaO6Cl3−x

High Resolution Electron Microscopy Investigations of La₂CeTaO₆Cl₃ and its Thermal Decomposition Product La₂Ce Ce TaO₆Cl_3?x The thermal decomposition of the hexagonal La₂CeTaO₆Cl₃ led to a mixed-valent product La₂CeCe TaO₆Cl_3?x with a complicated monoclinic structure. The detailed inspection shows two subunits A and B, which form the monoclinic unit cell by a ABAB sequence. The subunit A is almost identical to the hexagonal cell of the starting material while subunit B has additional Ln- and Cl-positions. For this reason, the main structure features of the monoclinic compound and the starting material are related, which is clearly seen in the electron microscopy investigations. As might be expected from the relationship between the subunits A and B one can observe defects in the monoclinic compound arising from the various possibilities of combining these building elements. We also found structure defects in the hexagonal starting material, which are caused by the presence of the subunit B.