Synthesis, crystal structure, and magnetic properties of oxynitride perovskites SrMn0.2M0.8O2.6N0.4 (M = Nb, Ta)

Abstract

Complex perovskites SrMn_0.2Nb_0.8O_2.6N_0.4 and SrMn_0.2Ta_0.8O_2.6N_0.4 were synthesized; these are rare examples of octahedral Mn²⁺ in oxynitride perovskites. Joint Rietveld refinement of neutron and X-ray data revealed that SrMn_0.2Nb_0.8O_2.6N_0.4 and SrMn_0.2Ta_0.8O_2.6N_0.4 had orthorhombic symmetries, in contrast with those of analogous perovskites SrM′_0.2M_0.8O_3−xN_x (M′ = Li, Na, Mg; M = Nb, Ta), which are all tetragonal. Both SrMn_0.2Nb_0.8O_2.6N_0.4 and SrMn_0.2Ta_0.8O_2.6N_0.4 exhibited paramagnetic behavior with effective magnetic moments of 5.60μ_B and 5.94μ_B, respectively, consistent with a high-spin Mn²⁺ (d⁵, S = 5/2) state. The Weiss constants were −24.7 K for SrMn_0.2Nb_0.8O_2.6N_0.4 and −15.4 K for SrMn_0.2Ta_0.8O_2.6N_0.4, indicating the presence of weak antiferromagnetic spin–spin interactions. The band gaps of SrMn_0.2Nb_0.8O_2.6N_0.4 and SrMn_0.2Ta_0.8O_2.6N_0.4 were determined to be 1.75 eV and 2.2 eV, respectively, suggesting that the Mn 3d electrons were essentially localized.