Strukturuntersuchungen an den Oxidnitriden SrTaO2N,CaTaO2N und LaTaON2 mittels Neutronen‐ und Röntgenbeugung

Structural Investigations on the Oxidenitrides SrTaO₂N, CaTaO₂N and LaTaON₂ by Neutron and X‐ray Powder Diffraction The crystal structures of the perovskite related oxidenitrides SrTaO₂N, LaTaON₂ and CaTaO₂N have been determined with special regard to the structures of the respective anionic partial structure. The structure refinements were performed by individual Rietveld analyses of both X‐ray and neutron powder diffractograms and in addition by joint refinements in order to confirm the results. Both refinement methods yield consistent structure solutions. At least the first two compounds have fully ordered anionic sublattices. The crystal structure of SrTaO₂N has been solved in the space group I4/mcm (a = 5.7049(3) Å, c = 8.0499(5) Å, R_p = 0.0706, R_wp = 0.0904, reflections: 70 (neutrons)/36 (X‐ray), R(F²)(n) = 0.147, R(F²)(X) = 0.0952), with an ordered anionic partial structure. LaTaON₂ crystallizes monoclinic (C2/m, a = 8.0922(3) Å, b = 8.0603(2) Å, c = 5.7118(2) Å, β = 134.815(1)°, R_p = 0.0592, R_wp = 0.0766, reflections: 235(n)/113(X), R(F²)(n) = 0.0944, R(F²)(X) = 0.165) and also shows a totally ordered distribution of the anions. In the case of CaTaO₂N (Pnma, a = 5.6239(3) Å, b = 7.8954(4) Å, c = 5.5473(3) Å, R_p = 0.0503, R_wp = 0.0656, reflections 206(n)/110(X), R(F²)(n) = 0.0985, R(F²)(X) = 0.0405) slightly unbalanced displacement parameters (neutron data, ordered O/N distribution model) hint at a partial exchange of oxygen and nitrogen.