Zur Darstellung und Struktur von LaTa7O19 Röntgenographische und elektronenmikroskopische Untersuchungen

Preparation and Structure of LaTa₇O₁₉. X-Ray and Electronmicroscopic Investigations In the system La₂O₃/Ta₂O₅ a new ternary compound LaTa₇O₁₉ could be prepared by chemical transport in a temperature gradient T₂ → T₁ (1120 → 1020°C; Cl₂ was added). LaTa₇O₁₉ is hexagonal, space group P6 with the lattice constants a = 6.23₆ and c = 19.99₅ Å. In the structure double layers of pentagonal TaO₇-bipyramids are recognizable perpendicular to [001]-direction. They alternate with a single layer consisting of La? O and Ta? O coordination polyhedra. Images of the structure were made with high resolution transmission electron microscopy along the [001]-direction. Despite the length of the axis the computer simulation based on the multi-slice method agreed well with the experimental images.