New scheelite-type oxynitrides in systems RWO3N-AWO4 (R = rare-earth element ; A = Ca, Sr) from precursors obtained by the citrate route
Résumé
RWO3N oxynitrides were isolated as single phases for R = Nd and Pr, after thermal ammonolysis of reactive precursors prepared using the citrate complexation/calcination route. Both stoichiometric compounds crystallize with a scheelite-type tetragonal unit cell, with a = 5.2821(3) Å, c = 11.5893(8) Å (NdWO3N) and a = 5.299(3) Å, c = 11.631(9) Å (PrWO3N). Neutron diffraction experiments performed on the Nd-phase did not evidence any oxygen/nitrogen order within the scheelite anionic subnetwork (S.G. I41/a). (Nd,A)W(O,N)4 (A = Ca, Sr) solid solution domains were identified between NdWO3N and the AWO4 oxide composition.
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