New series of honeycomb ordered oxides, Na3M2SbO6 (M(ii) = Mn, Fe, (Mn, Fe), (Mn, Co)): Synthesis, structure and magnetic properties

Article abstract of DOI:10.1039/c9dt01194c

New layered oxides, Na₃M₂SbO₆ (M(ii) = Mn, Fe) have been synthesized by solid state reactions under inert conditions. Rietveld refinements of the powder X-ray diffraction measurements confirmed the structures in the C2/m space group. The layered structure consists of honeycomb slabs with ordered M²⁺ (Mn or Fe) and Sb⁵⁺ cations, separated by Na⁺ ions in the interlayer octahedral sites. X-ray photoelectron spectroscopy measurements further substantiated the presence of Mn²⁺, Fe²⁺ and Sb⁵⁺ ions. A paramagnetic behavior has been exhibited by Na₃Mn₂SbO₆ in the range of 300-100 K with negative Weiss constant (θ = -144 K). Zero field cooled and field cooled values diverged below 50 K and without the indication of a long-range antiferromagnetic order down to 2 K. On the other hand, Na₃Fe₂SbO₆ has been found to display two different transitions in the magnetic susceptibility measurements. A distinct cusp appeared around T ～ 120 K followed by the divergence between the zero field cooled and the field cooled values. The observation of antiferromagnetic ordering (T_N ～ 7.5 K) suggested the magnetic frustration behavior arising out of the placement of Fe²⁺ ions in the triangular lattice of the honeycomb layers. Partial substitution of Mn²⁺ ions by Fe²⁺ and Co²⁺ ions has resulted in isostructural Na₃MnFeSbO₆ and Na₃MnCoSbO₆ under similar experimental conditions. Magnetic properties have been significantly modified by the coexistence of Mn²⁺ and Fe²⁺ ions in Na₃MnFeSbO₆. Co²⁺ substitution resulted in paramagnetic behavior with θ ～ -8.4 K confirming thereby the competing antiferromagnetic interactions. The scope of the present work has been explored by carrying out the ion-exchange experiments of the sodium analogues using molten salt (LiNO₃) to synthesize new Li₃M₂SbO₆ (M = Mn, Fe) oxides.

Full text of DOI:10.1039/c9dt01194c

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January 2016 Pages 1–398
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Efficient extraction of sulfate from water using
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New Series of Honeycomb Ordered Oxides, Na M SbO (M (II) = Mn, Fe, (Mn, Fe), (Mn,
3
2
6
Co)): Synthesis, Structure and Magnetic Properties†
Dileep Kumar Yadav, Aanchal Sethi, Shalu, and S. Uma*
Materials Chemistry Group, Department of Chemistry
University of Delhi, Delhi-110007, INDIA
Abstract
New layered oxides, Na M SbO (M (II) = Mn, Fe) have been synthesized by solid state
3
2
6
reactions under inert conditions. Rietveld refinements of the powder X-ray diffraction
measurements confirmed the structures in the C2/m space group. The layered structure consists
2
+
5+
+
of honeycomb slabs with ordered M (Mn or Fe) and Sb cations, separated by Na ions in the
interlayer octahedral sites. X-ray photoelectron spectroscopy measurements further substantiated
the presence of Mn , Fe and Sb5+ ions. A paramagnetic behavior has been exhibited by
2
+
2+
Na Mn SbO in the range of 300-100 K with negative Weiss constant ( = -144 K). Zero field
3
2
6
cooled and field cooled values diverged below 50 K and without the indication of a long-range
antiferromagnetic order down to 2 K. On the other hand, Na Fe SbO has been found to display
3
2
6
two different transitions in the magnetic susceptibility measurements. A distinct cusp appeared
around T ~ 120 K followed by the divergence between the zero field cooled and the field cooled
values. The observation of antiferromagnetic ordering (T ~ 7.5 K) suggested the magnetic
N
frustration behavior arising out of the placement of Fe2+ ions in the triangular lattice of the
honeycomb layers. Partial substitution of Mn2+ ions by Fe2+ and Co2+ ions has resulted in
isostructural Na MnFeSbO and Na MnCoSbO under similar experimental conditions. Magnetic
3
6
3
6
properties have been significantly modified by the coexistence of Mn2+ and Fe2+ ions in
2
+
Na MnFeSbO . Co substitution resulted in paramagnetic behavior with  ~ -8.4 K confirming
3
6
thereby the competing antiferromagnetic interactions. The scope of the present work has been
explored by carrying out the ion-exchange experiments of the sodium analogues using molten
salt (LiNO ) to synthesize new Li M SbO (M = Mn, Fe) oxides.
3
3
2
6
_
___________________________________________________________
*
Corresponding Author E-mail: suma@chemistry.du.ac.in
yadav331054bhu@gmail.com; aanchusethi22@gmail.com; shaluatri1992@gmail.com
†
Electronic supplementary information (ESI) available.
1

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1
. Introduction
Designing solid state structures by careful restriction of magnetic and nonmagnetic ions in
various lattice positions has proven to be successful for the experimental recognition of several
unusual magnetic materials. Mixed metal oxides possessing honeycomb lattices are favored in
this regard as shown by the recent report of the absence of magnetic ordering even at 0.05 K in
4
+
5
1
the Ir (5d ) containing quantum spin liquid, H LiIr O . The protonated oxide obtained by the
3
2
6
2
3
soft chemistry approach differs from the parent Na IrO or Li IrO oxides associated with large
2
3
2
3
frustration index |ϴ/T | values but are known to exhibit antiferromagnetic (AFM) ordering at 15
N
K. The honeycomb oxides are versatile and are known to accommodate several of the transition
metal ions (M) organized in such a way to form edge shared octahedral layers. Multiple cationic
5
+
5+
substitutions are possible where in each XO (X = Sb , Bi ) is surrounded by six MO
6
6
octahedra as realized in the layered oxides with stoichiometries
(A = Li, Na; X =
Bi, Sb; M (II) = Mg, Co, Ni, Cu, Zn).4-13 The combined edge shared M XO layers are further
2
6
separated by nonmagnetic layers of alkali metal ions. These layered structures are defined as
ordered rock salt structures with the simplest member being α-NaFeO . The various members
2
possessing honeycomb lattices offer an interesting class of materials to understand structure-
property relationships and for technological applications including electrodes for rechargeable
batteries, solid electrolytes and thermoelectric to mention a few.
+
+
Cu or Ag containing delafossite (CuFeO ) oxides also possess a similar edge shared
2
+
+
honeycomb M XO layers separated by linear nonmagnetic Cu or Ag ions and are equally
2
6
important as p-type transparent conductors.14 Cu and Ag containing delafossite oxides are
+
+
+
+
synthesized preferentially by topotactic reactions from the corresponding Li or Na ions
containing rock salt structures. The copper containing delafossites can also be obtained by
2

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conventional high temperature solid state preparations. Delafossites with ordered or disordered
cations in the M XO honeycomb pattern are known in compositions, Cu M XO (M = Mg, Co,
2
6
3
2
6
Ni, Cu, Zn; X = Sb, Bi).15-17 Complex magnetic properties and magnetic frustration are exhibited
by a wide variety of oxides belonging to the rock salt superstructure and delafossite structural
2
+
families because of the ordered arrangement of magnetic ions (M = Mn, Co, Ni Cu) in the
triangular lattice. As a result, competing next-nearest neighbor interactions (NNN) become as
significant as the nearest neighbor (NN) interactions for understanding their magnetic behavior.
For example, Cu IrO synthesized by topotactic reaction from Na IrO has also been found to be
2
3
2
3
1
8
+
magnetically frustrated exhibiting only a weak magnetic order at 2.7 K. Similarly, partial Cu
exchanged oxides, Cu NaIr O and Cu LiIr O respectively exhibited ferromagnetic like
3
2
6
3
2
6
magnetic frustration at 10 K and a clear antiferromagnetic (AFM) transition coupled magnetic
frustration behavior.19
Furthermore, long-range AFM ordering at low temperatures are known in Na M SbO (M = Ni,
3
2
6
Co),9,12,20 Na Co TeO , Li Ni SbO , Na Ni BiO and Li Ni BiO . In addition, Zvereva and
9
21
11
7
2
2
6
3
2
6
3
2
6
3
2
6
coworkers based on careful magnetization experiments coupled with theoretical calculations
have revealed a zigzag AFM ground state in A Ni SbO (A = Li, Na) arising from the
3
2
6
2
+
8
21,22
antiferromagnetic and non-negligible ferromagnetic interactions between the Ni (d ) ions.
1
1
The magnetic frustration has been exemplified by Cava et al in the case of Na Ni BiO and in
3
2
6
1
6
the delafossites, Cu M SbO (M = Co, Ni) as a result of a definite AFM transition (respective
3
2
6
TN = 18.5 and 22.3 K) together with the Weiss (respective θ = 6.5 (1) and -20.5 (2) K) constants.
2
+
9
Spin gap behavior arising from the presence of Cu (d ) in the honeycomb arrangement has
2
3
24
3+
5
been reported in Na Cu TeO and Na Cu SbO . Na FeSbO possessing Fe (d ) in high spin
2
2
6
3
2
6
4
6
25
failed to exhibit any long-range AFM ordering unlike its lithium analogue, Li FeSbO . The
4
6
3

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3
+
observed positive Weiss constant (θ = 140 K) has been linked to the presence of Fe in high spin
3
+
3+
3+
and in low spin, thus generating a ferromagnetic arrangement (Fe ↑- Fe -↓-Fe ↑). The electron
spin resonance (ESR) and Mӧssbauer spectroscopy studies revealed the existence of two
3
+
3+
5+
different Fe ions and the coexistence of low spin Fe ions with Sb ion in honeycomb layer
has been confirmed through DFT calculations. Li FeSbO displayed long-range AFM ordering (θ
4
6
=
-17 K; T = 3.6 K), as the spin frustrations in the triangular lattice are not sufficiently strong to
N
destroy AFM ordering.
Experimental investigation of magnetic properties in several mixed metal oxides is feasible
because of the flexible nature of the honeycomb lattice as demonstrated by the incorporation of
+
26,13
additional Li in the series of Li MTeO (M = Co, Ni, Cu, Zn)
and Li MSbO (M = Cr, Fe,
4 6
4
6
Mn, Al, Ga)26,27 oxides. Honeycomb oxides with extended miscibility based on the comparable
+
3+
28
sizes of Li and M ions have also resulted in Li (Li1.5xFe3-(x+1.5x)Te )O (0.1≤ x ≤ 1.0) and
3
x
6
2
9
Li M TeO (M = Cr, Mn, Al, Ga) members. The recent surge in the literature surrounding
4
.5 0.5
6
these rock salt based layered oxides stemmed out with the added intention of discovering new
3
0
31
32
electrode (eg. Na Ni BiO , Li NiTeO ) and electrolyte Na M TeO (M = Ni, Co, Zn, Mg)
3
2
6
4
6
2
2
6
5
+
5+
6+
materials. In general, honeycomb lattices investigated so far are based on Sb , Bi or Te ions
in combination with (3d) transition metal divalent (M = Co, Ni, Cu) ions and trivalent (M = Cr,
Mn, Fe) ions. As part of our ongoing efforts of studying novel oxides possessing honeycomb
2
+
5
2+
6
structures, we envisaged the possibility of synthesizing hitherto unknown Mn (d ) and Fe (d )
stabilized rock salt superstructure oxides by chemical tuning of the oxidation states of the
2
+
2+
transition metal cations. Incorporation of Mn and Fe ions without involving the reduction of
Sb5+ ions together with the presence of electropositive Na ions is experimentally quite
challenging. Few oxides of Mn2+ combined with Sb5+ ions alone have been reported earlier.
+
4

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Mn2+ containing MnSb O (S. G. P321) synthesized by Subramanian et al through high
2
6
temperature (>900 °C) reactions possessing a distorted triangular lattice has been reported to
3
3
have incommensurate magnetic structure. It is also possible to stabilize metastable MnSb O by
2
6
low temperature ion-exchange reactions in layered trigonal (S. G. P
) form by reacting
3
4
ilmenite NaSbO with MnSO -KCl-KBr melt at 470 °C in CO atmosphere. Nalbandyan and
3
4
2
coworkers have predicted an incommensurate magnetic structure for the metastable MnSb O
2
6
based on the observed 3D AFM ordering (below T = 8.5 K), a weak ferromagnetic signal
N
(
below T = 41.5 K) and further supported by DFT calculations. Fluorite related Mn Sb O has
2 2 7
3
5
been synthesized by solid state reactions at 100 °C , while a cubic pyrochlore Mn Sb O
7
2
2
exhibiting unconventional spin-glass behavior has been stabilized via low temperature
methods.36 The dimorphic Mn FeSbO containing Mn ions has been stabilized in the
2+
2
6
ferromagnetic ilmenite phase at high temperature (900 °) and pressure (3GPa) and the
antiferromagnetic perovskite phase has been stabilized at high temperature (900 °) and at a much
higher pressure of 6GPa.37,38 On the other hand, mixed metal oxides stabilized by Fe and Sb
2+
5+
have not been known till now. Even trial experiments to synthesize FeSb O by low temperature
2
6
reactions of NaSbO with FeSO -KCl-KBr melt around 500 °C in CO atmosphere resulted only
3
4
2
3
9
in a mixture FeSbO and Sb O . It is also imperative to point out the existence of honeycomb
4
2
3
O in delafossite, Cu Mn SbO , but the corresponding Fe2+ based
1
5
layers of
6 3 2 6
delafossite oxide is still unknown. In this work we report the successful synthesis of
Na Mn SbO and Na Fe SbO for the first time under inert conditions provided by an
3
2
6
3
2
6
atmosphere of argon. The possibility of synthesizing further substituted analogues,
Na MnFeSbO and Na MnCoSbO has been demonstrated. Structural elucidation of these
3
6
3
6
members together with the interesting magnetic properties are discussed in this paper.
5

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2
2
. Experimental section
.1 Synthesis
Na CO (Fischer scientific, 99.9 %), MnO (Sigma Aldrich, 99 %), FeO (Sigma Aldrich, 99.7 %),
2
3
Co O , (Sigma Aldrich, 99 %) and Sb O (Sigma Aldrich, 99.9 %) were used as reactants in the
3
4
2
3
synthesis. A precursor of NaSbO was obtained initially by heating a stoichiometric,
3
homogeneous mixture of Na CO and Sb O at 650 °C for 12 h, followed by 850 °C for 12 h.
2
3
2
3
Polycrystalline Na Mn SbO was synthesized by pelletizing the homogenized mixture of
3
2
6
NaSbO , MnO and Na CO in the ratio 1: 2: 1, placing the pellet on a platinum boat and heated at
3
2
3
8
20 °C for 16 h under flowing argon in a tubular furnace. The sample was subsequently cooled
to room temperature without disrupting the flow of argon. Approximately 0.2-0.5 % excess of
Na CO was used to compensate any loss due to volatilization. Similarly, Na Fe SbO was
2
3
3
2
6
synthesized by making a pellet of the homogenized mixture of NaSbO FeO and Na CO in the
3
,
2
3
ratio of 1: 2: 1. The pellet placed on an alumina boat was heated to 760 °C for 12 h under
flowing argon in the tubular furnace. The sample after first heat treatment was reground,
pelletized and heated again at 760 °C for another 12 h in argon. Na MnFeSbO was synthesized
3
6
by pelletizing the homogenized mixture of NaSbO , MnO, FeO and Na CO in the ratio 1: 1:1: 1
3
2
3
and heating the pellet at 770 °C for 12 h in arogon atmosphere. Similarly, Na MnCoSbO was
3
6
synthesized by heating a pellet obtained out of homogenizing the mixture of NaSbO , MnO,
3
+
Co O and Na CO in the ratio 1: 1:0.333: 1 at 900 °C for 12h in an atmosphere of argon. Li
3
4
2
3
ion-exchanged products were obtained by treating Na M SbO (M= Fe, Mn) oxides with excess
3
2
6
of molten LiNO (SRL, 99.5 %) at 300 °C in argon followed by washing with ethanol and drying
3
at room temperature under vacuum to get the ion-exchanged products.
2
.2 Characterization
6

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Powder X-ray diffraction (PXRD) measurements were carried out at room temperature using a
PANalytical X’Pert PRO diffractometer equipped with Cu Kα radiation (λ = 1.5418 Å). Data
were collected in the angular range of 2θ = 10-70° with a scan step width of 0.04° and a scan rate
of 6.5 s/step at 25 °C. Data for carrying out Rietveld refinements were collected in the angular
range of 2θ = 10-120° with a scan step width of 0.04° and a scan rate of 9.0 s/step at 25 °C. The
PXRD patterns were initially fitted using the Le Bail refinement followed by Rietveld
refinements using the GSAS+EXPGUI program.40,41 The elemental analysis of the samples were
performed on energy-dispersive spectrometer (EDS) employing a JEOL 6610LV microscope
operating at a voltage of 30 kV. Low temperature magnetic measurements were performed using
Physical Property Measurement System (PPMS), (Closed Cycle based Cryogen free system-
Cryogenics Limited, USA) in the temperature range 300-2 K under an applied field of 1000 Oe
and 100 Oe. Field dependent magnetization data were collected at 300 and 2K with applied
magnetic fields up to 5 T. X-ray photoelectron spectroscopy (XPS) measurements were carried
+
out using PHI 5000 versa prob II, FEI Inc., with Ar ion as well as C60 sputter gun at a pressure
-9
better than 10 Torr. First, the sample was cleaned by argon-ion bombardment in the sample
compartment to ensure that the surface was absolutely clean (without any contamination),
followed by its transfer to the analyzing chamber. The core level spectra were recorded using Al
Kα radiation at pass energy of 50 eV, an electron take off angle of 90°, and a resolution of 0.1
eV. The core level spectra were fitted after adjusting the baseline relative to the signal
background. The C 1s core level spectra at 284.6 eV were taken as reference for the charge
correction in the core level spectra, and for further calibration of the peak positions.
3
3
. Results and discussion
.1 Synthesis and Structure
7

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The standardization of the synthetic conditions to obtain single phase polycrystalline samples of
Na M SbO (M = Mn, Fe) required several experimental trials. Initial experimental attempts for
3
2
6
the preparation of manganese containing oxide involved the reaction of heating a mixture of
Na SbO and MnO in the ratio 1: 2 at various temperatures starting from 700 °C to 850 °C for a
3
4
duration of 12-24 h in an argon atmosphere. The PXRD patterns of the products suggested the
phase formation with a rock salt ordered structure but accompanied with the presence of more or
less an equivalent amount of NaSbO as an impurity phase. Subsequent trials were suitably
3
modified by taking NaSbO as the initial precursor. Powders obtained by mixing NaSbO , MnO
3
3
and Na CO in the ratio 1: 2: 1, when heated at 820 °C for 16 h, under flowing argon gas
2
3
successfully yielded monophasic pale yellow brown colored, rock salt ordered structure (Fig. 1).
Only a minimum amount of 0.2-0.5 % Na CO was added in excess in order to compensate for
2
3
possible volatilization and any further increase in the amount of Na CO resulted in producing
2
3
Na SbO as an impurity. A lower reaction temperature (760 °C) combined with an intermediate
3
4
grinding and reheating assisted in the successful formation of black colored Na Fe SbO starting
3
2
6
from NaSbO , Na CO and FeO (Fig. 2). FeO as a reactant has been found to be successful in
3
2
3
getting single phase products in spite of intrinsic iron deficiency. The synthesized samples
2
+
2+
containing Mn and Fe were found to be sensitive to air and are required to be stored under
vacuum to prevent their oxidation. A stringent balance between the stoichiometry, reaction
temperature and time duration coupled with an inert atmosphere provided by a regular argon
flow is crucial for the stabilization of monophasic Na Mn SbO and Na Fe SbO .
3
2
6
3
2
6
Compositions from EDS recorded for the respective products, Na Mn SbO and Na Fe SbO
6
3
2
6
3
2
confirmed the nominal ratio (3: 2 : 1) between Na: Mn: Sb and between Na: Fe: Sb (ESI Fig.
S1†). The PXRD pattern of Na Mn SbO (Fig. 1) bears close resemblance to the existing α-
3
2
6
8

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NaFeO based superstructure oxides. Various examples include Na M SbO (M = Co, Ni, Cu,
2
3
2
6
Zn, Mg),8,9,10,12 Na FeSbO , Li FeSbO ,
24
25,27
Li M BiO (M = Zn, Ni) and Na M BiO (M =
3 2 6 3 2 6
5,7
4
6
4
6
1
1
3-
Ni, Mg, Zn) . The ordering of (Mn SbO ) honeycomb layer alternating with the sodium
2
6
containing layers is confirmed by the superstructure reflections appearing in the 2θ range of 18-
5°. The indexing of the PXRD patterns is possible in the metrically equivalent trigonal (S. G.
3
P3 12), and monoclinic (S. G. C2/m) symmetries. Space group C2/m has been preferred because
1
of better structural fitting and along with the fact that this space group has been reported to have
the lowest calculated energy for the ordered honeycomb compounds.8,42,43 Furthermore, space
group of C2/c has not been considered because sufficient extra reflections corresponding to the
doubling of the c parameter indicating additional ordering within the honeycomb layers were
absent. The PXRD patterns therefore were indexed in space group C2/m. The refined lattice
parameters show a definite shift with larger a and b parameters as compared to the values of
4
3
Na Zn SbO (Table 1, Fig. 3). The overall observed increase in the volume are in accordance
3
2
6
2+
2+
44
with the octahedral ionic radii of (Mn (high spin) = 0.83 Å; Zn = 0.74 Å) ions. The Rietveld
refinements of the PXRD patterns were attempted using an initial structure model of
Na Co SbO . The refinement converged successfully without much deviation from the starting
3
2
6
model (Fig. 1, Table 1). The site occupancies of Sb and Mn were allowed to vary in order to
verify the mixing of these ions by restraining the thermal parameters. Individually, the
occupancies of both of these ions did not show any variation and were kept constant for further
refinement cycles. Independent ordered existence of Mn2+ and Sb5+ ions in the structure is
preferred based on the ionic size of Sb5+ (0.60 Å) and Mn (0.83 Å) ions along with the
difference in their charges. The site occupancies of Na1 and Na2 did not alter beyond the
permissible limits, confirming thereby the structure of Na Mn SbO (Table1). The crystal
2+
3
2
6
9

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4
5
structure is shown in Fig. 4 and the bond distances along with bond valence sum (BVS) values
are listed in Table 2. The Mn-O bond lengths are in the range 2.17-2.27 Å, as expected based on
2
+
2-
the ionic radii of Mn and O ions. Sb-O distances (1.99-2.01 Å) are similar to those found in
5
+
8
other Sb containing oxides. The calculated BVS values are agreeable with the oxidation states
2
+
5+
of Mn (1.96) and Sb (5.00) ions (Table 2).
The composition of Na Fe SbO resulted in the formation of rock salt superstructure phase (Fig.
3
2
6
4
). All the reflections in the PXRD pattern were indexed in C2/m space group (Fig. 2). The
refined lattice parameters displayed a decreasing trend in the a and b parameters as compared to
2
+
the a and b parameters of the rest of the M ions containing honeycomb oxides (Fig. 3(a) and
b)). Interestingly, the corresponding c × sin(β) value showed an upward shift (Fig. 3(c)). Finally,
in the plot of the unit cell volume of all the known (S.G. C2/m) Na M SbO (M = Co, Ni, Cu,
(
3
2
6
Zn, Mg) oxides including the compounds synthesized in the present study (Na Mn SbO ,
3
2
6
2
+
Na Fe SbO ) versus the M octahedral radii, the volume of Na Fe SbO exhibited a small
3
2
6
3
2
6
downward deviation (Fig. 3(d)). The slight reduction in the a and b parameters is possible by the
2
+
3+
inevitable oxidation of Fe giving rise to a small amount of Fe ions in Na Fe SbO concurrent
3
2
6
2
+
3+
with the octahedral ionic radius of Fe (high spin) (0.78 Å) and Fe (high spin) (0.645 Å). This
possibility is reflected in the observed black color of the sample together with a small amount of
sodium deficiency in the interlayer as indicated by an increase in the c × sin(β) values (Fig. 3(c)).
The net result has been an overall increase in the unit cell volume for Na Fe SbO (Fig. 3(d)).
3
2
6
While in the case of Na Mn SbO , the c × sin(β) value show a definite downward unlike its a and
3
2
6
b parameters thereby emphasizing that there is no sodium ion deficiency in the interlayer.
Essentially, the linear relationship arrived in the plot of the unit cell volumes of Na M SbO
3
2
6
1
0

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2
+
oxides versus the M octahedral ionic radii confirms the individual compositions and the ionic
2
+
2+
size corresponding to the high spin configurations of the Mn , Fe ions in the structure.
The initial atomic structural coordinates found in Na Co SbO fitted very well in the subsequent
3
2
6
Rietveld refinements of the PXRD data of Na Fe SbO (Fig. 2, Table 3). The site occupancies of
3
2
6
5
+
2+
+
Sb , Fe and Na ions were verified systematically for all the individual crystallographic sites.
The deviations in each case were found to be negligible proving the expected stoichiometry of
Na Fe SbO . It is again to be noted that neither additional superstructure reflections nor any
3
2
6
indications of cationic mixed occupancies during refinements were evident. The octahedra
2
+
surrounding Fe is found to be distorted with the bond distances varying in the range 2.13-2.17
Å. The rest of the Sb-O and Na-O bond lengths are in agreement with those values reported
2
+
5+
earlier. Finally, the appropriate BVS values are obtained for both Fe (1.91) and Sb (4.89) ions
(Table 4).
2
+
2+
5+
In order to further confirm the coexistence of Mn and Fe ions along with Sb ions, XPS
measurements were carried out for Na Mn SbO and Na Fe SbO oxides (ESI Fig. S2 and S3†).
3
2
6
3
2
6
The XPS core level spectra of Na Mn SbO consists of Mn 2p and Mn 2p1/2 peaks around
3
2
6
3/2
4
6
binding energies, 639.8 and 651.8 eV with an additional satellite peak at 644.2 eV. Similarly
presence of peaks at binding energies 528.8 and 538.2 corresponding to Sb 3d5/2 and Sb 3d3/2 are
also clearly observed. The binding energy for O 1s overlaps with the Sb 3d5/2 and deconvolution
results in binding energy of O 1s to be 531.2 eV and 530.2 eV respectively in Na Mn SbO and
3
2
6
Na Fe SbO . The small intensity peak appearing around 534 eV in both the oxides can be
3
2
6
assigned to the weakly adsorbed species. The observation of peaks at 709.0 (Fe 2p ) and 723.3
3
/2
2
+
eV (Fe 2p ) are related to the presence of Fe . Similarly characteristic peaks at binding
1
/2
5
+
energies 528.7 and 538.1 eV conclude the presence of Sb in Na Fe SbO .
3
2
6
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3
.2 Magnetic Properties
The magnetic susceptibility data for Na Mn SbO is shown in Fig. 5. The data indicates a broad
3
2
6
maximum below 100 K. A clear indication of a transition is noted at 50 K and below which the
divergence between zero-field cooled (ZFC) and field cooled (FC) susceptibilities appear (Fig.
5
(a)). The plot of the inverse susceptibility versus temperature follows a linear Curie-Weiss
behavior in the temperature range 300-100 K (Fig. 5(b)). The resultant effective magnetic
moment (µ = 8.34 μ ) is found to be higher than the expected spin only value for high spin
eff
B
Mn2+ (S = 5/2, µS.O. = 5.91 μ ) indicating more complex magnetic interactions. The Weiss
B
constant () is found to be -144 K. Long-range AFM ordering transition has not been observed
2
4
down to 2 K, resembling Na FeSbO . However, the latter does not show any Curie-Weiss
4
6
behavior in the range 300-2 K. Various magnetically active transition metal based honeycomb
structured oxides exhibit different T and  values depending upon the nature of dominant
N
interactions. Accordingly different types of spin ordering are possible that are supported by both
experimental and theoretical calculations.22 MnSb O made up of similar edge shared Mn
2+
2
6
octahedral layers has been found to be antiferromagnetic (T = 8.5(5) K,  = -17(2) K) because
N
of the formation of spin-frustrated triangles along with an appearance of weak ferromagnetic
3
4
signal below T = 41.5(5) K. For the present Na Mn SbO the very high negative value  (-144
3
2
6,
K) confirms the strong AFM interactions. In the magnetization experiments at T = 2 K, The
presence of the hysteresis with a coercivity value of 1470 Oe suggests competing ferromagnetic
interactions. As a result of magnetic frustration, a clear T is not reached even at very low
N
temperatures (2 K).
The investigation of magnetic features of Na Fe SbO is highly significant because of the
3
2
6
2
+
unavailability of Fe stabilized oxides, particularly in the honeycomb geometry as mentioned
1
2

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earlier. As of now, only FeTiO in the related ilmenite has been shown to exhibit
3
4
7
antiferromagnetic behavior with a Neel temperature (T ) of 52 K. The magnetic susceptibility
N
data of Na Fe SbO are shown in Fig. 6. A distinct cusp around T ~ 120 K is visible in the
3
2
6
magnetic susceptibility plot and below this temperature (120 K), the values of ZFC are lower
than the FC values (Fig. 6(a) inset). On decreasing the temperature further, another transition
possibly antiferromagnetic with T around 7.5 K is noticed in the ZFC measurements, while a
N
saturation of susceptibility values is seen in the measured FC susceptibility values. The onset of
TN confirms that the magnetic frustration is not strong enough to prevent the AFM ordering. The
magnetic frustration in Na Fe SbO is further confirmed by the absence of a linear Curie-Weiss
3
2
6
paramagnetic relation in the plot of the inverse magnetic susceptibility versus temperature (Fig.
(b)). Consequently, magnetic moment values deviated from expected paramagnetic moments in
the 300-120 K. Further extrapolation lead to high ( > -200 K) values. The appearance of cusp at
6
1
20 K also brings about the change in the slope (120-2 K) accompanied by a reduction in the  (-
7
0 K) value. The low temperature transition at 7.5 K also represents the temperature
4
8
corresponding to the freezing of spin-glass transition. These observations again suggest an
obvious competition leading to magnetic frustration between the ferromagnetic interactions in
the honeycomb (Fe-O-Fe) and intense long-range AFM interactions between the honeycomb
layers. It is further evident from the magnetization experiments during the application of field up
to 5 T (Fig. 6(c)). The hysteresis indicating a saturation is absent at 300 K, while a hysteresis
with a coercivity value of 2850 Oe is noticed at 2 K. The complex nature of the competing
magnetic interactions can also be seen in the drastic change in the frustration index (|/T |) from
N
3
2.1 (300-120 K) to 10.0 (120-2K). Additional investigation involving field-dependent
magnetization and heat capacity measurements near transition temperatures coupled with
1
3

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electronic structure calculations will help in further understanding of the prevailing exchange
interactions.
3
.2 Scope for further exploration of the honeycomb ordered structures
2
+
2+
The introduction of Mn and Fe ions in the honeycomb network opens up more interesting
prospects to expand the research on Na M SbO based compositions. In particular, the
3
2
6
2
+
2+
2+
compounds that can be derived by the combination of other divalent magnetic (Co , Ni , Cu )
2
+
2+
2+
2+
and nonmagnetic (Zn , Mg ) ions together with Mn or Fe ions offer plenty of scope for
further exploration. To begin with, we attempted to synthesize oxides of compositions,
Na MnFeSbO and Na MnCoSbO and they were successfully stabilized under argon
3
6
3
6
atmosphere similar to the individual parent oxides. The profile matching of the PXRD patterns
were carried out using Le Bail method in the monoclinic space group C2/m to get the refined
lattice parameters, (a = 5.4623 (12) Å, b = 9.3540 (19) Å, c = 5.7129 (10) Å, β = 108.651 (17)°,
3
V = 276.57 (8) Å for Na MnFeSbO and a = 5.4237 (4) Å, b = 9.3507 (13) Å, c = 5.6783 (5) Å,
3
6
3
β = 108.416 (10)°, V = 273.229 (30) Å for Na MnCoSbO (Figs. 7 (a) and 8 (a)). Preliminary
3
6
2
+
2+
2+
structural analysis did not indicate any visible ordering between Mn and Fe or between Mn
2
+
and Co ions within the honeycomb lattices. Confirmation for the structural stabilization of the
solid solutions is clearly evident from the correlation of unit cell volumes with the average
2
+
2+
2+
2+
octahedral ionic radii values of Mn and Fe (0.805 Å) and that of Mn and Co (0.785 Å)
(
Fig. 3(d)) ions. Substitution of Fe2+ and Co2+ for Mn2+ in Na Mn SbO results in expected
3
2
6
decrease of the unit cell parameters and volume. A strikingly interesting magnetic susceptibility
2
+
2+
behavior is registered for the Na MnFeSbO by the random mixing of Mn and Fe ions in the
3
6
same crystallographic sites. A clear divergence between ZFC and FC values starts appearing
from 300 K without much variation in the susceptibility values with temperature (Fig. 7 (b)). The
1
4

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separation widens below 40 K and the Curie-Weiss linear behavior is found to be absent. On the
2+
2+
other hand, partial substitution of Co for Mn , shows a typical paramagnetic behavior in the
whole temperature range with an AFM around 4.8 K (Fig. 8 (b)). The linear plot of the inverse
magnetic susceptibility with temperature results in 8.35 μ as against the calculated value of 7.07
B
μB. The experimentally observed magnetic moment is slightly higher possibly due to the effect of
spin-orbit coupling specially in the transition elements with more than half-filled d-orbitals. The
Weiss constant () is -8.4 K confirming the AFM ordering but the lower value suggests the
decrease in AFM interaction as compared to the parent Na Mn SbO ( = -144 K). The partial
3
2
6
2
+
2+
2+
2+
substitution of nonmagnetic ions such as Zn or Mg for Mn and Fe ions leading to various
honeycomb structured analogues are worth further investigation.
Another direction available for future studies would be to examine the ion-exchange capabilities
+
of the Na M SbO (M = Fe, Mn) oxides. The PXRD patterns of the Li exchanged products from
3
2
6
our initial trials indicated a reduction in the crystallinity but revealed the formation of Li+
exchanged products (ESI Fig. S4†). The lattice parameters by profile matching (S. G. C2/m ) are
found to be a = 5.3921 (26) Å, b = 8.9544 (30) Å, c = 5.2433 (21) Å, β = 113.051 (30)°, V =
3
2
1
32.95 (14) Å for Li Mn SbO and a = 5.2017 (14) Å, b = 8.946 (4) Å, c = 5.1642 (14) Å, β =
3
2
6
3
09.630 (29)°, V = 226.35 (9) Å for Li Fe SbO . The unit cell parameters and volume display
3
2
6
the expected decrease from the respective sodium containing parent oxides. It is important to
note that the lithium based compositions could only be synthesized by ion-exchange reactions
because invariably the synthetic experiments performed at high temperature (760 °C) under
argon atmosphere starting from individual reactants failed to yield single phase Li Mn SbO and
3
2
6
Li Fe SbO products.
3
2
6
Conclusion
1
5

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We prepared new layered monoclinic (S.G. C2/m) compounds, Na Mn SbO and Na Fe SbO by
3
2
6
3
2
6
solid state reactions under argon atmosphere. The structures confirmed by Rietveld refinements
are found to be isostructural to the existing rock salt superstructure based oxides (Na M SbO , M
3
2
6
2
+
=
Co, Ni, Cu, Zn, Mg) possessing honeycomb layers formed by the (2: 1) ordering of M and
5
+
Sb ions. Magnetic susceptibility measurements for Na Mn SbO show paramagnetic behavior
3
2
6
with a high negative value for Weiss constant without a firm long-range ordering even at very
low temperature (2 K). Na Fe SbO exhibit two different transitions, namely one in the form of a
3
2
6
cusp at 120 K and an AFM ordering with T (~ 7.5 K). The absence of Curie-Weiss behavior
N
and the resultant negative  values confirm the geometric frustration worth investigation.
2
+
2+
2+
Substitution of Mn ions by Fe and Co ions is possible as shown by the successful synthesis
of Na MnFeSbO and Na MnCoSbO oxides. They are isostructural with the parent oxide but
2
6
3
6
2
+
2+
differ in their physical properties. Partial substitution of Fe for Mn results in the divergence
2
+
2+
between the ZFC and FC measurements below 40 K. Partial substitution of Co for Mn leads
to paramagnetic behavior (300-50 K) with an indication of competing AFM ( = -8.4 K)
interactions. Low temperature ion-exchange experiments of the parent sodium oxides with
molten lithium analogues underline some of the future prospects associated with the present
study.
Conflicts of interest
There are no conflicts of interest to declare.
Accession codes
CSD -1915728 and CSD-1915729 contain the crystallographic data (CIF) for this paper. These
data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
1
6

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data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre,
2 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
Acknowledgements
We are thankful for the financial support received from DST- SERB (EMR/2016/006762) and
DU-DST PURSE grant phase-II. The authors also thank University Science and Instrumentation
(USIC, University of Delhi) for the use of facilities. We also gratefully acknowledge TIFR,
Mumbai for the initial magnetic measurements and Prof. R. Nagarajan, Department of
Chemistry, University of Delhi for constant support and discussion. DKY and SA thank CSIR
and UGC for fellowships respectively and AS thank DST-SERB for fellowship.
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7

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References
1) K. Kitagawa, T. Takayama, Y. Matsumoto, A. Kato, R. Takano, Y. Kishimoto, S. Bette, R.
Dinnebier, G. Jackeli, H. Takagi, Nature, 2018, 554, 341-345.
(
(
(
(
2) Y. Singh, P. Gegenwart, Phy. Rev. B, 2010, 82, 064412 (7 pp).
3) J. Chaloupka, G. Jackeli, G. Khaliullin, Phys. Rev. Lett., 2010, 105, 027204 (4 pp).
4) G. C. Mather, R. I. Smith, J. M. S. Skakle, J. G. Fletcher, M. A. Castellanos, M. P. Gutierrez,
A. R. West, J. Mater. Chem., 1995, 5, 1177-1182.
(5) C. Greaves, S. M. A. Katib, Mat. Res. Bull., 1990, 25, 1175-1182.
(6) J. M. S. Skakle, M. A. Castellanos, S. T. Tovar, A. R. West, J. Solid State Chem., 1997, 131,
1
15-120.
7) R. Berthelot, W. Schmidt, S. Muir, J. Eilertsen, L. Etienne, A. W. Sleight, M. A.
Subramanian, Inorg. Chem., 2012, 51, 5377-5385.
8) O. A. Smirnova, V. B. Nalbandyan, A. A. Petrenko, M. Avdeev, J. Solid State Chem., 2005,
78, 1165-1170.
9) L. Viciu, Q. Huang, E. Morosan, H. W. Zandbergen, N. I. Greenbaum, T. McQueen, R. J.
Cava, J. Solid State Chem., 2007, 180, 1060-1067.
10) V. V. Politaev, V. B. Nalbandyan, A. A. Petrenko, I. L. Shukaev, V. A. Volotchaev, B. S.
Medvedev, J. Solid State Chem., 2010, 183, 684-691.
11) E. M. Seibel, J, H. Roudebush, H. Wu, Q. Huang, M. N. Ali, H. Ji, R. J. Cava, Inorg.
Chem., 2013, 52, 13605-13611.
12) W. Schmidt, R. Berthelot, A. W. Sleight, M. A. Subramanian, J. Solid State Chem., 2013,
01, 178-185.
13) V. B. Nalbandyan, M. Avdeev, M. A. Evstigneeva, J. Solid State Chem., 2013, 199, 62-65.
(
(
1
(
(
(
(
2
(
1
8

Page 19 of 33
Dalton Transactions
View Article Online
DOI: 10.1039/C9DT01194C
(14) M. Marquardt, N. Ashmore, D. Cann, Thin Solid Films 2006, 496, 146-156.
(
15) R. Nagarajan, S. Uma, M. K. Jayaraj, J. Tate, A.W. Sleight, Solid State Sci., 2002, 4, 787-
92.
16) J. H. Roudebush, N. H. Andersen, R. Ramlau, V. O. Garlea, R. Toft-Petersen, P. Norby, R.
Schneider, J. N. Hay, R. J. Cava, Inorg. Chem., 2013, 52, 6083-6095.
17) J. H. Roudebush, G. Sahasrabudhe, S. L. Bergman, R. J. Cava, Inorg. Chem., 2015, 54,
203-3210.
18) M. Abramchuk, C. Ozsoy-Keskinbora, J. W. Krizan, K. R. Metz, D. C. Bell, F. Tafti, J. Am.
Chem. Soc., 2017, 139, 15371-15376.
7
(
(
3
(
(19) J. H. Roudebush, K. A. Ross, R. J. Cava, Dalton Trans., 2016, 45, 8783-8789.
(20) S. Derakhshan, H. L. Cuthbert, J. E. Greedan, B. Rahaman, T. Saha-Dasgupta, Phy. Rev. B,
2
007, 76, 104403-104407.
21) E. A. Zvereva, M. A. Evstigneeva, V. B. Nalbandyan, O. A. Savelieva, S. A. Ibragimov, O.
S. Volkova, L. I. Medvedeva, A. N. Vasiliev, R. Klingeler, B. Buechner, Dalton Trans., 2012,
1, 572-580.
22) E. A. Zvereva, M. I. Stratan, Y. A. Ovchenkov, V. B. Nalbandyan, J. Y. Lin, E. L. Vavilova,
(
4
(
M. F. Iakovleva, M. Abdel, A. V. Silhanek, X.-J. Chen, A. Stroppa, S. Picozzi, H. O. Jeschke, R.
Valent, A. N. Vasiliev, Phy. Rev. B, 2015, 92, 144401-144412.
(
23) M. Schmitt, O. Janson, S. Golbs, M. Schmidt, W. Schnelle, J. Richter, H. Rosner, Phy. Rev.
B, 2014, 89, 174403-174410.
24) E. A. Zvereva, I. A. Presniakov, M.-H. Whangbo, H.-J. Koo, T. V. Frantsuzenko, O. A.
(
Savelieva, A. V. Sobolev, V. B. Nalbandyan, P.-S. Shih, J.-C. Chiang, J.-M. Lee, J.-M. Chen, J.-
Y. Lin, B. Büchner, A. N. Vasiliev, Appl. Magn. Reson., 2015, 46, 1121-1145.
1
9

Dalton Transactions
Page 20 of 33
View Article Online
DOI: 10.1039/C9DT01194C
(25) E. A. Zvereva, O. A. Savelieva, Y. D. Titov, M. A. Evstigneeva, V. B. Nalbandyan, C. N.
Kao, J.-Y. Lin, I. A. Presniakov, A. V. Sobolev, S. A. Ibragimov, M. Abdel-Hafiez, Y.
Krupskaya, C. Jahne, G. Tan, R. Klingeler, B. Buchnerb, A. N. Vasiliev, Dalton Trans., 2013,
4
2, 1550-1566.
26) V. Kumar, N. Bhardwaj, N. Tomar, V. Thakral, S. Uma, Inorg. Chem., 2012, 51, 10471-
0473.
(
1
(
(
(
(
27) N. Bhardwaj, A. Gupta, S. Uma, Dalton Trans., 2014, 43, 12050-12057.
28) A. Gupta, V. Kumar, S. Uma, J. Chem. Sci., 2015, 127, 225-233.
29) S. Uma, A. Gupta, Mat. Res. Bull., 2016, 76, 118-123.
30) D. S. Bhange, G. Ali, D. H. Kim, D. A. Anang, T. J. Shin, M. G. Kim, Y. M. Kang, K.Y.
Chung, K. W. Nam, J. Mater. Chem. A, 2017, 5, 1300-1310.
31) M. Sathiya, K. Ramesha, G. Rousse, D. Foix, D. Gonbeau, K. Guruprakash, A. S. Prakash,
M. L. Doublet, J.-M. Tarascon, Chem. Commun., 2013, 49, 11376-11378.
32) M. A. Evstigneeva, V. B. Nalbandyan, A. A. Petrenko, B. S. Medvedev, A. A. Kataev,
Chem. Mater., 2011, 23, 1174-1181.
(
(
(33) J. N. Reimers, J. E. Greedan, M. A. Subramanian, J. Solid State Chem., 1989, 79, 263-276.
(34) V. B. Nalbandyan, E. A. Zvereva, A. Y. Nikulin, I. L. Shukaev, M.-H. Whangbo, H.-J. Koo,
M. Abdel-Hafiez, X.-J. Chen, C. Koo, A. N. Vasiliev, R. Klingeler, Inorg. Chem., 2015, 54,
705-1711.
1
(35) H.G. Scott, J. Solid State Chem., 1987, 66, 171- 180.
(36) H. D. Zhou, C. R. Wiebe, A. Harter, N. S. Dalal, J. S. Gardner, J. Phys.: Condens. Matter.,
2
008, 20, 325201 (5pp).
2
0

Page 21 of 33
Dalton Transactions
View Article Online
DOI: 10.1039/C9DT01194C
(
37) G. V. Bazuev, B. G. Golovkin, N. V. Lukin, N. I. Kadyrova, Yu. G. Zainulin, J. Solid State
Chem., 1996, 124, 333-337.
38) A. P. Tyutyunnik, G. V. Bazuev, M. V. Kuznetsov, Yu. G. Zainulin, Mater. Res. Bull.,
011, 46, 1247-1251.
39) A. Y. Nikulin, E. A. Zvereva, V. B. Nalbandyan, I. L. Shukaev, A. I. Kurbakov, M. D.
Kuchugura, G. V. Raganyan, Yu. V. Popov, V. D. Ivanchenko, A. N. Vasiliev, Dalton Trans.,
017, 46, 6059-6068.
40) A. C. Larson, R. B. Von Dreele, General Structure Analysis System (GSAS); Los Alamos
National Laboratory Report LAUR 86-748; Los Alamos National Laboratory: Los Alamos, NM,
004.
(
2
(
2
(
2
(
(
41) B. H. Toby, J. Appl. Crystallogr., 2001, 34, 210-213.
42) J. Bréger, M. Jiang, N. Dupré, Y. S. Meng, Y. Shao-Horn, Ge. Ceder, C. P. Grey, J. Solid
State Chem. 2005, 178, 2575-2585.
43) W. Schmidt, R. Berthelot, A. Sleight, M. Subramanian, J. Solid State Chem., 2013, 201,
78-185.
(
1
(
(
(
44) R. D. Shannon, Acta Cryst. A, 1976, 32, 751-767.
45) I. D. Brown, J. Appl. Cryst., 1996, 29, 479-480.
46) J. F. Moulder, W. F. Stickle, P. E. Sobol, K. D. Bomben, J. Chastain, In: Chastain, J., Ed.
Handbook of X-Ray Photoelectron Spectroscopy: A Reference Book of Standard Spectra for
Identification and Interpretation of XPS Data, Perkin-Elmer Corporation, Waltham, 1992.
(
47) A. T. Raghavender, N. H. Hong, K. J. Lee, M.-H. Jung, Z. Skoko, M. Vasilevskiy, M .F.
Cerqueira, A. P. Samantiueke, J. Magn. Magn. Mater., 2013, 331, 129-132.
48) R. Havlicek, J. P. Vejpravova, D. Bochenek, J. Phys. Conf. Ser., 2010, 200, 012058 (4).
(
2
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Figure captions
Fig. 1 (a) PXRD pattern of Na Mn SbO and (b) Rietveld refinement of PXRD pattern of
3
2
6
Na Mn SbO . Experimental data (red), calculated profile (green), difference profile (pink) are
3
2
6
shown and vertical bars indicate Bragg positions. Digital image of the sample is shown as inset
in (a).
Fig. 2 (a) PXRD pattern of Na Fe SbO and (b) Rietveld refinement of PXRD pattern of
3
2
6
Na Fe SbO . Experimental data (red), calculated profile (green), difference profile (pink) are
3
2
6
shown and vertical bars indicate Bragg positions. Digital image of the sample is shown as inset
in (a).
Fig. 3 (a) (b) Variation in the lattice parameters for known Na M SbO oxides plotted against
3
2
6
M2+ octahedral ionic radii (data for Cu2+ has not been included because of Jahn-Teller
2
+
distortion). (c) Plot c × sin(β) versus M octahedral ionic radii. (d) Variation of unit cell volume
2
+
for known Na M SbO versus M octahedral ionic radii. The error bars associated with each
3
2
6
data point are smaller than the size of the data markers.
Fig. 4 (a) Crystal structure of Na M SbO (M = Mn, Fe) in bc plane. (b) Honeycomb array of
3
2
6
edge-shared MO octahedra.
6
Fig. 5 (a) Field-cooled (FC) and zero-field-cooled (ZFC) molar magnetic susceptibility of
Na Mn SbO as function of temperature (measuring field 0.1 T). The inset shows the low
3
2
6
temperature region of the susceptibility data. (b) Inverse magnetic susceptibility measured in a
magnetic field of 0.1 T (c) Magnetization curves at 300 K and 2 K.
Fig. 6 (a) Temperature- dependent magnetic susceptibility (χ) of Na Fe SbO measured with an
3
2
6
applied magnetic field of 0.1 T. The inset highlights the low temperature part of the magnetic
susceptibility recorded in zero-field cooled (ZFC) and field-cooled (FC) conditions. (b) Inverse
2
2

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magnetic susceptibility measured with an applied magnetic field of 0.1 T. (c) Field-dependent
magnetization (M) of Na Fe SbO (up to 5 T) at 300 K and 2 K.
3
2
6
Fig. 7 (a) PXRD pattern, Le Bail fit, Bragg reflections and difference plot for Na MnFeSbO .
3
6
(b) Temperature dependence of the magnetic susceptibility recorded in the ZFC and FC regimes
at B = 0.01 T for Na MnFeSbO .
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Fig. 8 (a) PXRD refinement of Na MnCoSbO . Observed (red), calculated (green), and
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difference (pink) plot is shown, and Bragg reflections are indicated by black tick marks.
b) Temperature dependence of the magnetic susceptibility recorded in the ZFC and FC regimes
at B = 0.01 T for Na MnCoSbO .
(
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Fig. 1
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Fig. 2
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Fig. 3
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Fig. 5
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(a)
Fig. 6
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