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Preparation, Crystal Chemistry, and Hidden Magnetic Order in the Family of Trigonal Layered Tellurates A2Mn(4+)TeO6 (A = Li, Na, Ag, or Tl)статья
Статья опубликована в высокорейтинговом журнале
Статья опубликована в журнале из списка Web of Science и/или Scopus- Авторы: Nalbandyan Vladimir B., Shukaev Igor L., Raganyan Grigory V., Artem Svyazhin, Vasiliev Alexander N., Zvereva Elena A.
- Журнал: Inorganic Chemistry
- Год издания: 2019
- Издательство: American Chemical Society
- Местоположение издательства: United States
- DOI: 10.1021/acs.inorgchem.8b03445
- Аннотация: We report the first four magnetic representatives of the trigonal layered A2M(4+)TeO6 (here, M = Mn) family. Na2MnTeO6 was synthesized from NaMnO2, NaNO3, and TeO2 at 650−720 °C, but analogues for which A = Li and K could not be obtained by direct synthesis. However, those for which A = Li, Ag, and Tl (but not K) were prepared by exchange reactions between Na2MnTeO6 and the corresponding molten nitrates. The oxygen content was verified by redox titration. According to the X-ray diffraction Rietveld analysis, the four new compounds are isostructural with Na2GeTeO6, trigonal (P3̅1c), based on ilmenite-like layers of edge-shared oxygen octahedra occupied by Mn(4+) and Te(6+) in an ordered manner. These layers are separated by cations A, also in a distorted octahedral coordination. However, off-center displacement of Tl+ is so strong, due to the lone-pair effect, that its coordination is better described as trigonal pyramid. Each MnO6 octahedron shares two opposite faces with AO6 octahedra, whereas TeO6 octahedra avoid sharing faces. Besides this double-layered structure, Na2MnTeO6 was often accompanied by a transient triple-layered rhombohedral polytype. However, it could not be prepared as a single phase and disappeared on annealing at 700−720 °C. All A2MnTeO6 samples (A = Ag, Li, Na, or Tl) revealed the unusual phenomenon of hidden magnetic order. Low-field magnetic susceptibility data exhibit a Curie− Weiss type behavior for all samples under study and do not show any sign of the establishment of long-range magnetic order down to 2 K. In contrast, both the magnetic susceptibility in sufficiently high external magnetic fields and the zero-field specific heat unambiguously revealed an onset of antiferromagnetic order at low temperatures. The frustration index f = Θ/TN takes values larger than the classical values for three-dimensional antiferromagnets and implies moderate frustration on the triangular lattice.
- Добавил в систему: Зверева Елена Алексеевна