Abstract
Oxynitride complex perovskites, BaMn0.2M0.8O2.6N0.4 (M = Nb, Ta), were prepared by reacting the layered oxides Ba5M4O15 with MnCl2, in the NH3 atmosphere. Both BaMn0.2M0.8O2.6N0.4 phases crystallized in orthorhombic symmetries, in contrast with previous Ba-based perovskite oxynitrides, BaMO2N and BaM'0.2M0.8O3−xNx (M′ = Li, Na, Mg; M = Nb, Ta), all of which were cubic. The thermogravimetry (TG) and differential scanning calorimetry (DSC) of AMn0.2M0.8O2.6N0.4 (A = Sr, Ba; M = Nb, Ta) suggested that the phase stability is higher for A = Ba and M = Ta than for A = Sr and M = Nb, respectively. Both BaMn0.2Nb0.8O2.6N0.4 and BaMn0.2Ta0.8O2.6N0.4 exhibited paramagnetic behavior with effective magnetic moments of 5.75 μB and 5.90 μB, respectively, well consistent with the high-spin Mn2+ state. All the four members of AMn0.2M0.8O2.6N0.4 had negative Weiss constants (θW's), indicative of the antiferromagnetic interactions. The variations of the θW among AMn0.2M0.8O2.6N0.4 were attributable to the differences in the Mn–O bond lengths (A = Sr vs. Ba) or to the distinct lattice covalency (M = Nb vs. Ta).
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