ic8b03445_si_001.pdf (695.08 kB)
Preparation, Crystal Chemistry, and Hidden Magnetic Order in the Family of Trigonal Layered Tellurates A2Mn(4+)TeO6 (A = Li, Na, Ag, or Tl)
journal contribution
posted on 2019-04-17, 17:40 authored by Vladimir B. Nalbandyan, Igor L. Shukaev, Grigory V. Raganyan, Artem Svyazhin, Alexander N. Vasiliev, Elena A. ZverevaWe 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.
History
Usage metrics
Categories
Keywords
double-layered structureMagnetic OrderMnO 6 octahedron sharesX-ray diffraction Rietveld analysisTeO 6 octahedra2 Kredox titrationtriple-layered rhombohedral polytypeAO 6 octahedrailmenite-like layersCrystal Chemistryedge-shared oxygen octahedra2 MnTeO 6 samplesexchange reactionssusceptibility data exhibitlone-pair effectoxygen contentNaMnO 2antiferromagnetic orderNa 2 MnTeO 6LiTlfrustration index foctahedral coordinationTrigonal Layered TelluratesNaNO 3AgNa 2 GeTeO 6TeO 2
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC