Excess antimony induced 12R Ba4Sb0.85Mn3.15O12 phase and Mn3O4 exsolution from 10H Ba5Sb0.7Mn4.3O15: crystal structure and magnetic properties
Journal of Solid State Chemistry(2024)
摘要
Hexagonal perovskite manganite has attracted much attention due to its rich structural chemistry and magnetic properties. The transformation between BaMxMn1−xO3 polymorphs can be caused by the change in substitution level or oxygen vacancies. In this study, we find a new polymorph change from 10H Ba5Sb0.7Mn4.3O15 (P63/mmc) to 12R Ba4Sb0.85Mn3.15O12 (R 3¯ m) via a ‘topochemical’ reaction with excess Sb2O3. The 10H Ba5Sb0.7Mn4.3O15 structure contains BaO3 layers in a (cchhh)2 sequence and face-shared MnO6 tetramers (Mn4 clusters), while the 12R Ba4Sb0.85Mn3.15O12 structure consists of BaO3 layers in a (cchh)3 stacking and face-shared MnO6 trimers (Mn3 clusters). The 10H → 12R phase conversion accompanies the exsolution of the Mn3O4 phase in trace amounts. For both 10H Ba5Sb0.71Mn4.29O15 and 12R Ba4Sb0.85Mn3.15O12, the Mn3+ cation on the corner-shared octahedra at M1 sites mediated competing ferromagnetic and antiferromagnetic exchanges between the magnetic Mn3 and Mn4 clusters, leading to spin-freezing transition at TF ≈ 11–15 K. The 10H → 12R phase change leads to an abrupt change of 2 K saturation moment from Ms ≈ 0.1 μB of 10H Ba5Sb0.71Mn4.29O15 to Ms ≈ 1.75 μB of 12R Ba4Sb0.85Mn3.15O12.
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