Journal of Solid State Chemistry 197 (2013) 543–549

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Synthesis, crystal structure, and properties of KSbO3-type Bi3Mn1.9Te1.1O11

Man-Rong Li a, Maria Retuerto a, Yong Bok Go a, Thomas J. Emge a, Mark Croft b, Alex Ignatov b,Kandalam V. Ramanujachary c, Walid Dachraoui d, Joke Hadermann d, Mei-Bo Tang e, Jing-Tai Zhao e,Martha Greenblatt a,n

a Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, NJ 08854, USAb Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854, USAc Department of Chemistry and Biochemistry, Rowan University, 210 Mullica Hill Road, Glassboro, NJ 08028, USAd EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgiume Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, Shanghai 200050, PR China

a r t i c l e i n f o

Article history:

Received 3 April 2012

Received in revised form

9 July 2012

Accepted 11 July 2012Available online 24 July 2012

Keywords:

KSbO3-type crystal structure

Bi3M3O11

Metal–metal interaction

X-ray absorption near edge spectroscopy

Magnetism

96/$ - see front matter & 2012 Elsevier Inc. A

x.doi.org/10.1016/j.jssc.2012.07.038

esponding author. Fax: þ1 732 445 5312.

ail address: martha@rutchem.rutgers.edu (M.

a b s t r a c t

Single crystals of Bi3Mn1.9Te1.1O11 were prepared from NaClþKCl flux. This compound adopts KSbO3-

type crystal structure as evidenced by electron and single crystal X-ray diffraction analysis. The three-

dimensional channel structure is formed by corner-sharing octahedral (Mn0.63Te0.37)2O10 dimers and

two identical (Bi1)4(Bi2)2 interpenetrating lattices. The intra-dimer Mn/Te–Mn/Te distances in

Bi3Mn1.9Te1.1O11 are short and are consistent with weak metal–metal interactions. The mixed oxidation

state of manganese and the edge-sharing octahedral features are confirmed by X-ray near edge

absorption spectroscopy measurements, which indicate Bi3(MnIII1.1MnIV

0.8)TeVI1.1O11 with 57.7% Mn3þ and

42.3% Mn4þ . The partial substitution of Te for Mn perturbs long-range magnetic interactions, thereby

destroying the ferromagnetic ordering found in Bi3Mn3O11 (TC¼150 K).

& 2012 Elsevier Inc. All rights reserved.

1. Introduction

Bi3M3O11 (BMO, M¼Al/Sb [1], Ga/Sb [1–3], Ti/W [4], Ru [5–8],Re [9,10], Os [6], and Pt [11]) family of oxides, crystallizing inKSbO3 (KSO)-type structure (cubic, space group Pn-3), have beenintensely studied in the last two decades, due to their interestingproperties including ionic conductivity, electrocatalysis [5,12],photocatalysis [13], and electromagnetism [7,10,13]. Bi3GaSb2O11

was first reported by Sleight and Bouchard in 1973 [2] with astructure made up of edge-shared M2O10 octahedral dimerslinked by sharing corners to form a three-dimensional (3D) tunnelnetwork and two identical interpenetrating lattices of [(Bi1)4

(Bi2)2] (Fig. 1). However, the atomic displacement parameters(ADPs) of Bi1 (8e site in Pn-3) were very large and highlyanisotropic compared with the other atoms, which was attributedto positional site disorder and the diffusion of Bi ions in the largeBi2O3-type channels, as Bi enrichment on the surface of thematerials was observed [1]. Subsequent neutron diffraction stu-dies suggested a Bi-site defect model (Bi1 at 8e site splits aroundits 3-fold axis to 24h site) to best account for the disorderADPs [3]. The MO6 octahedra are severely distorted as the intra-dimer metal ions appear to displace away from each other to

ll rights reserved.

Greenblatt).

overcome the electrostatic repulsion; for example, the discrepancyin M–O distance is up to 0.20 and 0.28 A in Bi3GaSb2O11 andBi6Ti5WO22, respectively [3,4]. Another interesting peculiarity ofKSO-phases is that they can accommodate different oxygen quan-tities varying from ABO3 to ABO3.667 due to their open structure.Thus, with transition metal (TM) ions of variable valences, inter-esting electronic and magnetic properties are possible. However,BMO are difficult to prepare because they require stringent reactionconditions in order to achieve the high oxidation state for the Mcations. Only a limited number of d-electron rich 4d- and 5d-heavyTM compounds with this structure have been reported. Bi3Re3O11

was first prepared under high pressure (4.5 GPa at 1150 1C) byCheetham and Rae-Smith in 1981 [9]. Later, in 2007, Sato et al.made it at much lower pressure (150 MPa) via hydrothermalmethod [10], and showed it to be a Pauli paramagnet. Bi3Ru3O11

[6] and Bi3Os3O11 [6,11] have been prepared in sealed quartz or Autubes under ambient pressure or 3 GPa [11], respectively. Bi3Ru3O11

is metallic and shows possible non-Femi liquid behavior of theelectrons, while Bi3Os3O11 has a metallic to semiconductor transi-tion at 125 K. Surprisingly, short intra-dimer metal–metal distances(M–M)Intra were observed in Bi3Ru3O11 and Bi3Re3O11 [5–7,14].

More recently, the first KSO-type BMO with 3d-TM, Bi3Mn3O11,was successfully prepared under high pressure (6 GPa). It isbelieved to posses randomly distributed Mn5þ and Mn3þ

(Bi3Mn3þMn5þ2 O11) or Mn4þ (Bi3Mn4þ

2 Mn5þO11) ions, and itsoxygen content can vary (–0.5rdr0.6) without changing the

Fig. 1. Crystal structure of Bi3M3O11 view along [1 1 1] (a) and [1 1 0] (b) directions (Bi and O1 were omitted for clarity), respectively, showing the 3D open framework

structure formed by corner sharing of edge shared M2O10 dimers; M2O10 octahedral dimers, blue; split Bi1, green; Bi2, brown; O1 inside channels (only shared by Bi),

purple. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 2. SAED patterns of Bi3Mn1.9Te1.1O11 with basic reflections indexed in Pn-3 with cell parameter of a¼9.38 A.

M.-R. Li et al. / Journal of Solid State Chemistry 197 (2013) 543–549544

cubic structure and semiconducting behavior [15,16]. More inter-estingly, its magnetic properties can change from antiferromag-netic (AFM) (TN¼45 K for d¼�0.5) to ferromagnetic (FM)(TC¼307 K for d¼0.6, a new record high TC among insulating/semiconducting ferromagnets). The discovery of Bi3Mn3O11

renewed interest in these types of materials. Recently, the Fe-analog, Bi3Fe1.68Te1.32O11, was prepared at ambient pressure viaconventional solid state reaction by replacing 44% of the Fe sitesby Te6þ , yielding Fe only in the 3þformal oxidation state [17].Attempts to stabilize Bi3Mn3O11 by partial Sb5þ-substitution ofMn at ambient pressure were unsuccessful and yielded pyro-chlore phases, as it is difficult to maintain the high formal valenceof Mn in edge-shared octahedral dimers at ambient pressure [13].

Compared with partial Sb5þ substitution for Mn, Te6þ-sub-stitution can lead to lower formal valence of Mn in Bi3Mn3�x-

TexO11, and possibly stabilize the phase at ambient pressure.In this work we synthesized a new Bi3Mn3O11-type phase, Bi3Mn1.9-

Te1.1O11 (BMTO) at ambient pressure by partial substitution of Mnby Te. Single crystals of BMTO were grown from NaClþKCl flux; thecrystal structure and magnetic properties are herein reported.

2. Experimental

Single crystals of BMTO were grown from NaCl (Fisher Scientific,99.0%) and KCl (Fisher Scientific, 99.0%) flux (mole ratio of NaCl/KCl¼0.506/0.494, with melting at 657 1C, NaClþKCl flux binaryphase diagram in Fig. S1 in Supporting Information (SI)). A stoichio-metric mixture of Bi2O3, MnCO3, and TeO2, and eightfold excess offlux, NaClþKCl (weight based) was loaded into a quartz tube, theraw mixture was heated at 750 1C for 10 day, followed by coolingdown to 550 1C with a cooling rate of 2 1C/h before the furnace was

switched off. The open–end of the quartz tube was exposed toair during the reaction (schematic diagram for BMTO synthesis inFig. S2 in SI). Finally, the flux was washed away with distilled water.

Single crystal structure determination of BMTO was performedon an Enarf–Nonius CAD4 diffractometer equipped with graphitemonochromatized Mo Ka radiation (l¼0.71073 A). Data collectionwas controlled by the CAD4/PC program package. Computationswere performed with the SHELX97 program package [18]. Energydispersive X-ray (EDX) analysis was carried out with a JEOL 5510scanning electron microscope (SEM) equipped with the OxfordINCA system. Selected area electron diffraction (SAED) patternswere obtained with a Philips CM20 transmission electron micro-scope. High resolution transmission electron microscopy (HRTEM)images were obtained on a Tecnai G2 transmission electron micro-scope. The Mn and Te X-ray absorption near edge spectra (XANES)were collected simultaneously in both the transmission and fluor-escence mode on beam line X-19A at the Brookhaven NationalSynchrotron Light Source. The dc magnetic susceptibility measure-ments were carried out on a physical properties measurementssystem (PPMS, Quantum Design). Typical zero field cooling (ZFC)and field cooling (FC) susceptibilities were studied under anexternal field of 1000 Oe in the temperature range 2.5–300 K. Thefield-dependent magnetization isotherms were studied at T¼2.5 Kin the range �5 T to 5 T.

3. Results and discussion

3.1. Crystal structure

The as-grown BMTO crystals are dark brown and exhibitoctahedral morphology (the sides as large as 50 mm, see Fig. S3

M.-R. Li et al. / Journal of Solid State Chemistry 197 (2013) 543–549 545

in SI). EDX analysis yields the atomic ratio of BMTO as Bi: Mn:Te¼0.49(2): 0.32(2): 0.196(9) from which the chemical composi-tion was assessed to be: Bi2.92(8)Mn1.9(1)Te1.18(5)Ox. A tilt series ofSAED patterns were collected for this sample as shown in Fig. 2.The brightest reflections on these patterns can be indexed in acubic unit cell with the cell parameter aE9.38 A, and relevantreflection conditions: hkl: no conditions, hhl: no conditions, 0kl:kþ l¼2n and 00l: l¼2n, which lead to space groups Pn-3 or Pn-

3m. Very weak extra reflections are present. To index these extrareflections we have used a tetragonal unit cell setting withparameters a¼b¼12.88 A and c¼18.22 A, the SAED patternsreindexed in these cell parameters are shown in Fig. S4 in SI.However, by taking Fourier transforms of different areas inseveral HRTEM images, it was clear that these extra reflectionsoccur only very locally and that also on the Fourier transformsthey barely rise above the noise. A representative HRTEM image isshown in Fig. 3, and includes a calculated HRTEM image (at focus

Fig. 3. HRTEM image of Bi3Mn1.9Te1.1O11. A calculated HRTEM image using the

model refined in this paper is added, indicated by a white border. The Fourier

transform of the area of this image is shown in the left bottom corner.

Table 1Crystallographic parameters and structure refinement details for Bi3Mn

Temperature 100 K

Empirical formula Bi3Mn1.94Te1.06O

Formula weight 1045.69

Wavelength (A) 0.7103

Crystal system Cubic

Space group Pn-3 (2 0 1)

Unit cell dimensions (a/A) 9.3733(15)

Volume (V/A3) 823.5(2)

Z 4

Density (calculated) (g cm�1) 8.434

Absorption coefficient (mm�1) 70.554

F(0 0 0) 1764

Crystal size (mm3) 0.19�0.19�0.1

Color Dark brown

Theta range for data collection 4.35�31.511

Index ranges �13rh, k, lr1

Reflections collected 9458

Independent reflections 462 (Rint¼0.059

Completeness to theta 98.7%

Absorption correction Numerical

Max. and min. transmission 0.0277 and 0.02

Refinement method Full-matrix least

Data/restraints/parameters 462/6/34

Goodness-of-fit on F2 1.001

Final R indices [I42sigma(I)] R1¼0.0365 wR2

R indices (all data) R1¼0.0380 wR2

Largest diff. peak and hole (e A�3) 2.388 and–2.540

value f¼�180 A and thickness t¼137 A) with the structure asrefined below in Pn-3 symmetry and shows excellent agreement.No systematic deviations from this symmetry are discernible byeye on the HRTEM images. A possible origin for these weak extrareflections could be short range order between Mn and Te, orbetween oxygen and vacancies.

Single crystal X-ray diffraction analysis is in good agreementwith the SAED results in the cubic system (space group Pn-3,a¼9.3842(9) and 9.3733(15) A at 100 and 293 K, respectively, forthe X-ray data). Details of the X-ray data collection and structuralrefinement are summarized in Table 1. The crystallographicparameters are listed in Table 2 and Tables S1-2 in SI. The refinedresults suggest a nominal composition of Bi3Mn1.94(4)Te1.06(4)O11,within one standard deviation of the EDX results of Bi2.92(8)

Mn1.9(1)Te1.18(5)Ox. Bi atoms are located at 24h (x, y, y; Bi1) and4b (0, 0, 0; Bi2) of Pn-3, respectively. The Mn and Te atoms arerandomly placed at 12g positions, and there are three crystallogra-phically independent oxygen sites: O1, O2, and O3 at 8e (0, 0, z), 12f(x, ¼, ¼) and 24h (x, y, z), respectively. The mixed M-site was refined

1.9Te1.1O11 at 100 and 293 k.

293 K

11 Bi3Mn1.94Te1.06O11

1045.69

0.7103

Cubic

Pn-3 (2 0 1)

9.3842(9)

826.40(14)

4

8.397

70.283

1764

8 0.19�0.19�0.18

Dark brown

4.34�31.47

3 �13rh, k, lr13

9497

0) 462 (Rint¼0.0590)

98.7%

Numerical

62 0.0278 and 0.0263

-squares on F2 Full-matrix least-squares on F2

462/6/34

1.004

¼0.0866 R1¼0.0489 wR2¼0.1003

¼0.0876 R1¼0.0493 wR2¼0.1006

2.220 and–2.482

Table 2

Atomic coordinates and equivalent isotropic displacement parameters (A2� 103)

for Bi3Mn1.9Te1.1O11 at 293 and 100 K. Ueq is defined as one third of the trace of

the orthogonalized Uij tensor.

Atom Site Occupancy x y z Ueq

Bi1 24h 1/3 0.3972(6) 0.3754(3) 0.3754(3) 28(1)

Bi2 4b 1 0 0 0 28(1)

Mn/Te 12g 0.647/0.353(13) 0.4016(2) 3/4 1/4 14(1)

O1 8e 1 0.1467(8) 0.1467(8) 0.1467(8) 10(2)

O2 12f 1 0.6142(13) 1/4 1/4 20(2)

O3 24h 1 0.5926(9) 0.2464(10) 0.5372(9) 18(2)

Bi1 24h 1/3 0.3972(4) 0.3753(2) 0.3753(2) 24(1)

Bi2 4b 1 0 0 0 24(1)

Mn/Te 12g 0.649/0.351(11) 0.4016(1) 3/4 1/4 12(1)

O1 8e 1 0.3533(6) 0.3533(6) 0.1467(6) 9(2)

O2 12f 1 0.6140(10) 1/4 1/4 15(2)

O3 24h 1 0.5919(7) 0.2467(8) 0.5365(8) 16(1)

Table 3

Selected bond lengths (A), angles (1) and bond valence sums for Bi3Mn1.9Te1.1O11

at 100 and 293 K.

100 K 100 K

Bi1– O1 �2 2.192(6) 2.195(8)

O1 �1 2.366(7) 2.369(9)

O2 �1 2.625(8) 2.630(10)

O3 �1 2.658(8) 2.671(10)

O3 �1 2.698(7) 2.710(10)

O2 �2 2.879(5) 2.884(7)

O3 �1 2.897(8) 2.909(10)

oBi1–O4 2.598(7) 2.613(9)

BVS 3.02 2.99

Bi2– O1 �2 2.381(6) 2.384(8)

O3 �6 2.491(7) 2.495(8)

oBi2–O4 2.464(7) 2.467(8)

BVS 2.97 2.944

Mn/Te– O2 �2 1.909(7) 1.910(9)

O3 �2 1.948(7) 1.950(9)

O3 �2 2.002(8) 1.998(8)

oMn/Te–O4 1.953(7) 1.953(9)

BVS 4.23 4.23

O2–Mn/Te–O2 83.8(1) 83.7(1)

O2–Mn/Te–O3 88.6(2) 88.9(3)

O2–Mn/Te–O3 90.7(2) 90.5(3)

O2–Mn/Te–O3 91.9(2) 91.8(3)

O2–Mn/Te–O3 172.3(2) 172.5(3)

O3–Mn/Te–O3 87.3(3) 87.3(4)

O3–Mn/Te–O3 90.5(3) 90.7(4)

O3–Mn/Te–O3 99.1(3) 98.5(4)

O3–Mn/Te–O3 176.5(3) 176.9(3)

M.-R. Li et al. / Journal of Solid State Chemistry 197 (2013) 543–549546

to be Mn/Te¼0.649/0.351. No evidence of oxygen non-stoichiometryhas been found in BMTO from the refinement and oxygen variationstudy (Fig. S5-6 and Table S2 in SI).

BMTO adopts the KSO-type 3D network structure (Fig. 1). Fig. 4illustrates a schematic view of the unit cell structure with onlythe Bi sublattice at 293 K of eight Bi1 and four Bi2 atoms ((Bi1)8

(Bi2)4) per unit cell. Bi2 adopt a face-centered cubic arrangement,while two identical (Bi1)4 tetrahedra (highlighted by purple dashedlines in Fig. 4a, with Bi1–Bi1 distances of 3.678 (9) A) are locatedaround two of the tetrahedral interstitial sites of the Bi2 closedpacked lattice (highlighted by the cyan dashed line in Fig. 4a) andform two identical (Bi1)4(Bi2)2 interpenetrating lattices. Bi1 iscoordinated to 9 O atoms in a distorted tri-capped trigonal prism(Table 3 and Fig. 4b) with Bi1–O distances between 2.195(8) and2.909(10) A. Bi2 is coordinated to 8 O atoms in a cube and adopts atypical lone-pair cation environment on a threefold axis with twoBi2–O1 at 2.384(8) A and six Bi2–O2 at 2.495(8) A (Table 3 andFig. 4b). Note that the Bi1–O1 and Bi2–O1 distances are signifi-cantly shorter than those for O2 and O3, due to the influence of the6s2 lone-pair electrons of Bi3þ and the oxygen coordinationenvironment as observed in Bi12(Bi0.5Fe0.5)O19.5 [19] and Bi2CdO4

[20]. Bi1O9 bonding is not typical for a lone-pair electron cation,but similar coordination was observed in Bi2M2O7 (M¼Ru and Ir)pyrochlores [21,22], while Bi2 adopts the typical lone-pair cationenvironment (Table 3 and Fig. 4a). As discussed earlier, Bi1 wasplaced at the general (24h) site and triply disordered (occupancy of1/3); this yields reasonable ADPs, a better overall refinement, andreasonable bond valence sums (BVS) [23] for Bi1 and Bi2 of 2.99and 2.94, respectively.

Fig. 5 shows a slab (thickness of �5.41 A) of the (Mn0.63Te0.37)O6

octahedral open-framework structure at 293 K with the O1 atomsisolated in the channels and only shared by Bi1 and Bi2 (Table 3 andFig. 4). The adjacent O2–O2 edge-shared (Mn0.63Te0.37)2O10 dimersare perpendicular to each other and linked into a 3D network viasharing O3 corners. The average M–O distance in the (Mn0.63

Te0.37)O6 octahedron is 1.953(9) A, and is comparable to the sumof the effective ionic radii of 1.959 A for M with 36.67% Mn3þ ,26.66% Mn4þ , and 36.67% Te6þ [24]. The (M–M)Intra distance(highlighted by blue dashed lines in Fig. 5) is 2.846(2) A, which islonger than that of a perfect edge-shared octahedral dimer, 2.76 Afor (Mn0.63Te0.37)–O distance of 1.953 A. The BVS value of the

Fig. 4. Unit cell structure of Bi3Mn1.9Te1.1O11 showing the Bi sublattice and coordinat

omitted for clarity). (a) Two (Bi1)4 tetrahedra (highlighted by purple dashed lines) ar

dashed lines) of face-centered Bi2 arrangement, forming two identical (Bi1)4(Bi2)2 int

forming a distorted cube coordination (light blue, top left); (b) Bi1is nine coordi

(For interpretation of the references to color in this figure legend, the reader is referre

(Mn0.63Te0.37) site, 4.23 is in good agreement with that expected,4.33 for M in Bi3M3O11 compounds.

At 100 K, the crystal structure of BMTO is comparable to thatat 293 K (Table S1 in SI). BMTO is thermally more stable than thehigh pressure phase Bi3Mn3O11 as reflected by Table S3 in SI. Biatoms are apparently over-bonded in Bi3Mn3O11 (BVS of 3.12 and3.39 for Bi1 and Bi2, respectively), while the Mn-site appears to

ion environment (the views are slightly tilted along the a axis, Mn/Te atoms are

e seated around the two (Bi2)4 tetrahedral interstitial sites (highlighted by cyan

erpenetrating structure. Bi2 is surrounded by eight oxygen atoms (bottom right),

nated (up) to be a distorted tri-capped trigonal prism (down, yellow green).

d to the web version of this article.)

Fig. 5. A slab of framework (thickness �5.41 A, a little tilt-viewing along [1 0 0]

direction) linked by edge-shared (O2�O2) octahedral (Mn0.63Te0.37)2O10 dimmers

via corner-sharing (O3) in Bi3Mn1.9Te1.1O11. O1 are isolated to the framework.

The (M–M)Intra and (M–M)Inter are highlighted by blue and red dashed lines,

respectively. Bi atoms are not shown for clarity.

Fig. 6. Variation of (a) unit cell a (A) and (b) average bismuth–oxygen bond

lengths /Bi–OS (A) with (M–M)Intra in Bi3M3O11. The M ions with dn- and d0-

electronic configurations are shown as circles and squares, respectively.

M.-R. Li et al. / Journal of Solid State Chemistry 197 (2013) 543–549 547

be under-bonded, as the BVS of Mn is smaller (less than 4.13,Table S3 in SI) than the expected value of 4.33. This bondingmismatch likely causes a large tension inside the crystal structurerequiring high pressure for its synthesis. A structural relaxationmay occur when some Mn is replaced by Te, as reflected in theideal BVS for the Bi and the Mn/Te sites, and explains why BMTOcan be prepared under ambient pressure.

The average valence of M in KSO-type BMO compounds isþ4.33. This high formal valence is unfavorable for edge-sharedoctahedral dimers due to electrostatic repulsion. As shown inTable S4 and Fig. S7 in SI, most observed (M–M)Intra arelonger than the expected values in ideal octahedral dimers [24].The (M–M)Inter increases with increasing ionic radii, while the(M–M)Intra is independent of ionic radii (Fig. S7a). Although thereis some discrepancy between different reports, the (M–M)Intra

appears to be smaller in different BMO compounds with dn-electronic configuration (n40) than those with d0 (Table S4 andFig. S7a). All the reported (M–M)Intra are below 2.933 A (inBi3Pt3O11 [11], average Pt4.33þ radii of 0.607 A) for dn ions exceptBi3Mn1.68Te1.32O11, in which the M site is over diluted by Te6þ

(Table S4) [17], and above 2.946 A (in Bi3AlSb2O11 [1], averageionic radii of 0.578 A) for d0 ions. Thus, apparently, the presenceof d-electrons shortens (M–M)Intra in BMO, indicating weakmetal–metal interactions; this bonding is assumed to be respon-sible for the greater stability and ease of formation of compoundsof d-electron rich TM, than those with fewer d electrons, such asBi3Mn3O11. The unit cell parameters and bond lengths are alsoindependent of effective ionic radii of M, since both the unit cellparameters (Fig. 6a) and Bi–O bond lengths (Fig. 6b) increase withincreasing (M–M)Intra distances, further evidence that an optimal(M–M)Intra distance is the key factor in the stability of BMO.

3.2. XANES studies

To confirm the oxidation states of Mn, Bi and Te, XANESmeasurements were carried out for BMTO. In the comparison ofthe Te–L1 edges of BMTO and Te4þO2 standard (Fig. S8), the Te6þ

state for BMTO is confirmed by the dramatic 4.6 eV shift of itswhite line feature to higher energy relative to that of Te4þO2.

Both L1 and L3 edge measurements confirmed the Bi3þ characterin BMTO (not shown).

In Fig. 7 the Mn–K edge of BMTO is compared to a series ofoctahedrally coordinated Mn standards with formal valencesvarying between Mn2þ and Mn4þ . The main edge features at 3d

transition metal K edges are dominated by 1s to 4p transitions.These features, and the continuum onset, which lies underneaththem, manifest a chemical shift to higher energy with increasingvalence. The 4p features can also be split into multiple features bythe local atomic coordination/bonding and by admixed 3d con-figurations. Despite this complication several characteristics canbe noted in Fig. 7. The first is the consistent chemical shift of theedge to higher energy with increasing formal valence. The secondis that: while corner sharing octahedral, perovskite-based com-pound spectra exhibit a single sharp 4p, B-feature peak; there is asystematic B1/B2-feature splitting in the spectra of compoundswith edge sharing octahedra.

In Fig. 7 (top) a particularly sharp 4p, B-feature can be seen inthe perovskite based Mn2þ standard Sr2MnReO6 which has onlycorner sharing of the MnO6 octahedra [25]. In contrast the NaClstructure MnO spectrum, which has edge sharing octahedra [26],shows a splitting of this feature into B1 and B2 features. The B1-and B2-features are, respectively shifted down and up in energywith the midpoint between the two is close to the energy of thesingle B-feature of the corner sharing compound.

Fig. 7. The Mn–K edge spectra for a series of octahedral Mn compounds with

varying valence (2þtop, 3þ/3.5þcenter and 4þbottom) and inter-octahedral

connections. The dash-dotted lines are perovskite related, corner sharing octahe-

dral standards: Sr2Mn2þReO6, LaMn3þO3, and CaMn4þO3. The dotted lines are

NaCl-spinel related standards with edge sharing octahedra: Mn2þO, LiMn3.5þ2 O4,

and l-Mn4þO2. The Bi3Mn1.9Te1.1O11 spectra, with its dimer edge sharing

octahedral unit corner linked into a 3D structure, are compared to both the

middle and bottom standards.

Fig. 8. ZFC and FC magnetic susceptibility curves of Bi3Mn1.9Te1.1O11 measured

at 0.1 T.

Fig. 9. Isothermal magnetization (M) vs magnetic field (H) loops of Bi3Mn1.9-

Te1.1O11 measured at 2.5 K between �5 and 5 T.

M.-R. Li et al. / Journal of Solid State Chemistry 197 (2013) 543–549548

The Mn3þ perovskite-based (corner sharing octahedra) stan-dard LaMnO3 spectrum, in Fig. 7 (middle), manifests a prominentin B-feature [27,28] that is substantially chemical shifted tohigher energy relative to that of the Mn2þ , Sr2MnReO6. TheMn3.5þ , spinel structure LiMn2O4 spectrum, in Fig. 7 (middle)can be seen to exhibit split B1/B2-features. The spinel structure isknown to consist of crossing chains of edge-sharing octahedra[29–31]. Thus the correlation of the split B1/B2-features with anedge sharing octahedral structure is again evidenced.

In Fig. 7 (bottom) the Mn4þ standard spectra for the perovs-kite-based (corner sharing octahedra) CaMnO3 [27,28] and for thespinel structure l-MnO2 [31] are shown. Once again the cornersharing CaMnO3 spectrum exhibits a single B-feature whereas theedge sharing l-MnO2 spectrum exhibits split B1/B2-featuresshifted up and down from the single B-feature. The chemicalshift of the CaMnO3 B-feature to higher energy relative to theMn3þ , LaMnO3 B-feature should also be noted.

In Fig. 7 the Mn–K edge of BMTO is overlaid on the Mn3þ/Mn3.5þ standards (middle) and the Mn4þ standards (bottom).Several points should be noted in these comparisons. First, theBMTO spectrum shows a split B1/B2-feature character, consistentwith the dimer edge sharing octahedra in the Mn–Te sites in itscrystal structure. Second, this splitting is less robust than in thestandards which are consistent with a single edge shared

octahedra in the M2O10 dimers in this compound versus themultiple shared edges in the standards. Third the corner and edgesharing in BMTO causes a broadening of the Mn–K edge for thiscompound. Fourth, comparison to the Mn4þ standards in Fig. 7(bottom) indicates a Mn valence of less than Mn4þ in BMTO.Finally, comparison of the BMTO spectrum to the Mn3.5þ stan-dard in Fig. 7 (middle) is broadly consistent with expected formalvalence of Mn3.42þ , within the substantial uncertainties intro-duced by the different local structures relative to the standard.

3.3. Magnetic properties

The temperature variation of the magnetic susceptibility ofBMTO in Fig. 8 exhibits an increase with decreasing temperature.At low temperatures, a divergence between the ZFC and FC curves isobserved. The ZFC curve indicates a decay of the susceptibilitywhere it deviates from FC curve. This divergence below �5 K isusually related to the presence of a cluster-glass state, lacking long-range coherence. The substitution of Te for Mn in the structureseems to destroy the long range magnetic interactions, with an FM-like transition (TC¼150 K) present in Bi3Mn3O11 [15]. The magne-tization versus magnetic field plot at T¼2.5 K (Fig. 9) presents a

M.-R. Li et al. / Journal of Solid State Chemistry 197 (2013) 543–549 549

small curvature that is not exactly AFM as in the case ofBi3Mn3O10.5, an AFM with a TN¼45 K [16]. The properties of themagnetization isotherm seem to be consistent with the formationof some sort of glassy state which is not surprising given thedisorder of the compound. The spin glass behavior could explainthe small hysteresis. At high temperatures the reciprocal suscept-ibility does not follow a linear, characteristic Curie–Weiss behavior.The noticeable deviation may indicate that some magnetic correla-tions also take place at high temperatures, even if there is no long-range magnetic order. This is supported by the remnant suscept-ibility found at high temperatures (not shown) that could be relatedto the establishment of short range magnetic interactions betweenMn cations inside the dimers or it could also be related to a Pauliparamagnetism induced by delocalized electrons, as it has beenshown in other oxides of the this family like Ba2Ir3O9 [32].

4. Conclusion

We have prepared single crystals of a new member of theBi3M3O11 family with composition Bi3Mn1.9Te1.1O11. The electronand single crystal diffraction analyses indicate that Bi3Mn1.9-

Te1.1O11 adopts a KSbO3-type crystal structure. The mixed oxida-tion state of manganese is evidenced by the stoichiometry,established by EDX, and confirmed by XANES as Bi3(MnIII

1.1MnIV0.8)-

TeVI1.1O11 with the co-existence of 57.7% Mn3þ and 42.3% Mn4þ .

The intra-dimer metal–metal distance in (Mn0.63Te0.37)2O10 sug-gests a weak interaction, as observed in other B3M3O11 with Mcontaining dn-electrons. Compared with Bi3Mn3O11, the Te sub-stitution in Bi3Mn1.9Te1.1O11 relaxes the crystal structure, andenables stabilization under ambient conditions in contrast to thehigh pressure required for the synthesis of Bi3M3O11. However,since the Te substitution is in the Mn site, it interferes with thelong-range magnetic order, and only short-range magnetic order-ing below 5 K is observed. This work reveals that M ions, whichcontain dn-electrons, dramatically affect the crystal structure andphysical properties due to the metal–metal interaction thatshortens the intra-dimer metal–metal distances. This study sug-gests possible new compounds in this family, including Bi3(MIII-

MIVMVI)O11 at ambient pressure, and Bi3MIV2 MVO11 at high

pressure.

Acknowledgement

This work was supported by the NSF-DMR-0966829 grant. Wealso would like to thank Dr. Umut Adem at the University ofLiverpool for useful discussions.

Appendix A. Supporting information

Supplementary data associated with this article can be foundin the online version at http://dx.doi.org/10.1016/j.jssc.2012.07.038.

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