%0 Journal Article
%A Nalbandyan, Vladimir B.
%A Shukaev, Igor L.
%A Raganyan, Grigory V.
%A Svyazhin, Artem
%A Vasiliev, Alexander N.
%A Zvereva, Elena A.
%D 2019
%T Preparation, Crystal Chemistry, and Hidden Magnetic
Order in the Family of Trigonal Layered Tellurates A2Mn(4+)TeO6 (A = Li, Na, Ag, or Tl)
%U https://acs.figshare.com/articles/journal_contribution/Preparation_Crystal_Chemistry_and_Hidden_Magnetic_Order_in_the_Family_of_Trigonal_Layered_Tellurates_A_sub_2_sub_Mn_4_TeO_sub_6_sub_A_Li_Na_Ag_or_Tl_/8008442
%R 10.1021/acs.inorgchem.8b03445.s001
%2 https://ndownloader.figshare.com/files/14920376
%K double-layered structure
%K Magnetic Order
%K MnO 6 octahedron shares
%K X-ray diffraction Rietveld analysis
%K TeO 6 octahedra
%K 2 K
%K redox titration
%K triple-layered rhombohedral polytype
%K AO 6 octahedra
%K ilmenite-like layers
%K Crystal Chemistry
%K edge-shared oxygen octahedra
%K 2 MnTeO 6 samples
%K exchange reactions
%K susceptibility data exhibit
%K lone-pair effect
%K oxygen content
%K NaMnO 2
%K antiferromagnetic order
%K Na 2 MnTeO 6
%K Li
%K Tl
%K frustration index f
%K octahedral coordination
%K Trigonal Layered Tellurates
%K NaNO 3
%K Ag
%K Na 2 GeTeO 6
%K TeO 2
%X 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.
%I ACS Publications