Synthesis and crystal structure of novel Ruddlesden-Popper strontium niobium oxynitrides

The family (SrO)(SrNbO2-xN)(n) is the first example of Ruddlesden-Popper strontium niobium oxynitrides and provides layered structures to obtain mixed valence niobium compounds with a variety of oxidation states and transport properties. We have prepared members with n = 1 (Sr2NbO3N) and n = 2 (Sr3Nb2O5N2) by solid state reaction of Nb2O5 and SrCO3 at 900-1050 degreesC under ammonia flow. These compounds crystallize in the I4/mmn space group and show a range of anionic stoichiometry that together with the N/O ratio determines the formal oxidation state for niobium and therefore the resultant physical properties. Samples of the n = I member show mixed valence Nb5+/Nb4+ and are paramagnetic and very resistive at room temperature. This behavior may be understood by considering electron localization due to N/O disorder. (C) 2003 Elsevier Science Ltd. All rights reserved.