Layered Oxychlorides [PbBiO2]An+1BnO3n−1Cl2 (A = Pb/Bi, B = Fe/Ti):Intergrowth of the Hematophanite and Sillen PhasesMaria Batuk,*,† Dmitry Batuk,† Alexander A. Tsirlin,‡ Dmitry S. Filimonov,§ Denis V. Sheptyakov,∥

Matthias Frontzek,∥ Joke Hadermann,† and Artem M. Abakumov†,§

†Electron Microscopy for Materials Science (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium‡National Institute of Chemical Physics and Biophysics, 12618 Tallinn, Estonia§Department of Chemistry, Moscow State University, 119991 Moscow, Russia∥Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232Villigen, PSI Switzerland

*S Supporting Information

ABSTRACT: New layered structures corresponding to the general formula[PbBiO2]An+1BnO3n−1Cl2 were prepared. Pb5BiFe3O10Cl2 (n = 3) andPb5Bi2Fe4O13Cl2 (n = 4) are built as a stacking of truncated An+1BnO3n−1perovskite blocks and α-PbO-type [A2O2]

2+ (A = Pb, Bi) blocks combinedwith chlorine sheets. The alternation of these structural blocks can berepresented as an intergrowth between the hematophanite and Sillen-typestructural blocks. The crystal and magnetic structures of Pb5BiFe3O10Cl2 andPb5Bi2Fe4O13Cl2 were investigated in the temperature range of 1.5−700 Kusing X-ray and neutron powder diffraction, transmission electron microscopyand 57Fe Mossbauer spectroscopy. Both compounds crystallize in the I4/mmm space group with the unit cell parameters a ≈ ap≈ 3.92 Å (a unit-cell parameter of the perovskite structure), c ≈ 43.0 Å for the n = 3 member and c ≈ 53.5 Å for the n = 4member. Despite the large separation between the slabs containing the Fe3+ ions (nearly 14 Å), long-range antiferromagneticorder sets in below ∼600 K with the G-type arrangement of the Fe magnetic moments aligned along the c-axis. The possibility ofmixing d0 and dn cations at the B sublattice of these structures was also demonstrated by preparing the Ti-substituted n = 4member Pb6BiFe3TiO13Cl2.

1. INTRODUCTION

Many inorganic materials have modular structures, whereindividual units are responsible for different functions. The[Bi2O2]

2+ slabs with the α-PbO type structure as well as simplehalide layers (Cl− or Br−) are effective spacers in some layeredfunctional materials. The Aurivillius intergrowth phases consistof perovskite blocks sandwiched between the [Bi2O2]

2+ slabsand can be described with a general formula [Bi2O2]-An−1BnO3n+1, where A is a large alkali, alkali-earth, rare-earth,or Pb2+ cation and B is a d0 transition metal cation, such as W6+,Nb5+, Ta5+, or Ti4+ (Figure 1a). The Aurivillius phases areprone to polar distortions due to cooperative displacements ofthe A cations in the perovskite blocks coupled to cooperativeoctahedral tilting.1,2 Many Aurivillius phases demonstrateferroelectricity with high Curie temperatures.3 Insertion ofthe halide layers between the [Bi2O2]

2+ slabs gives rise to aplethora of complex intergrowth structures.4 The Sillen-Aurivillius (SA) phases (Figure 1b)5−11 are built of perovskiteblocks, [Bi2O2]

2+ slabs and sheets of one or several halidelayers. The stacking sequence of these modules corresponds toa general formula [Bi2O2][An−1BnO3n+1][Bi2O2][Xm], where nis the number of perovskite layers and m is the number ofhalide layers.The current interest in materials that combine electrical and

magnetic orders leads to a natural question whether magnetic

dn cations could be incorporated into the Aurivillius and SAstructures. However, the range of such replacements within theperovskite blocks is limited because of difficulties inmaintaining the charge balance. In both structures, the

Received: January 19, 2015Revised: March 20, 2015

Figure 1. Perovskite-based intergrowth structures: (a) Aurivilliusstructure [Bi2O2]An−1BnO3n+1; (b) Sillen-Aurivillius intergrowth[Bi2O2]An−1BnO3n+1Clm; (c) Ruddlesden−Popper An+1BnO3n−1Cl2;(d) hematophanite An+1BnO3n−1Cl. Orange spheres correspond toBi/A atoms, green to Cl, and blue to O; octahedra and pyramids arecentered with B cations.

Article

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© XXXX American Chemical Society A DOI: 10.1021/acs.chemmater.5b00233Chem. Mater. XXXX, XXX, XXX−XXX

perovskite blocks are oxygen-excessive, as reflected by theAn−1BnO3n+1 formula. This favors the d0 cations with largeformal charges (W6+, Nb5+, Ta5+, Ti4+) and restricts the fractionof the dn cations with smaller charges to be accommodated inthese structures. For example, one-third of the Ti4+ cations hasbeen replaced with trivalent Cr3+, Fe3+, or Mn3+ in the SA phaseBi5PbTi3O14Cl, whereas compensating for the reduced chargein the B sublattice by simultaneous substitution of Pb2+ byBi3+.12 However, because of a random distribution of Ti4+ andmagnetic dn ions, the Bi6Ti2MO14Cl materials demonstratespin-glass behavior. The fraction of the dn transition metalcations can be increased only at the cost of increasing thicknessof the perovskite blocks (i.e., increasing n in the An−1BnO3n+1formula), as demonstrated by inserting the perovskite BiMO3(M = Cr, Fe) fragments into the Bi4Ti3O12 Aurivillius phase.

2,13

However, this approach faces natural limitations imposed bysteadily increasing difficulties in the preparation of single-phasedefect-free compounds with large n.In contrast to the Aurivillius and SA phases, oxychlorides

based on the Ruddlesden−Popper (An+1BnO3nCl with n =114−20 or An+1BnO3n−1Cl2 with n = 2, 3,15,18,19,21−24, Figure 1c)and hematophanite (An+1BnO3n−1Cl, n = 2, 3, Figure 1d)25−36

structures readily accommodate magnetic B cations. In bothstructural families, the substitution of oxygen layers by layers ofhalogen ions transforms BO6 octahedra into BO5 squarepyramids at the terminal layers of the perovskite block. Thesetruncated oxygen-deficient perovskite blocks are able toaccommodate B cations of lower valence.The crystal structure of the mineral hematophanite

Pb4Fe3O8Cl (Figure 1d) is built of the truncated perovskitePb4Fe3O8 blocks alternating with layers of chlorine atoms,forming a Pb2Cl layer at the interface with CsCl-typeordering.26,27,32 Recently, we proved that the thickness of theperovskite block in hematophanite can be increased from oneto two octahedral layers forming the n = 4 Pb4BiFe4O11Cl andPb5Fe3TiO11Cl compounds.37,38 According to the neutronpowder diffraction study, the hematophanite and the successivePb4BiFe4O11Cl member of the series demonstrate robustantiferromagnetic order with the G-type arrangement of theFe3+ magnetic moments and relatively high Neel temperatures∼600 K.32,37 To the best of our knowledge, ferroelectricity hasnever been reported for the hematophanite-based structures.In this contribution, we demonstrate that intergrowing of the

truncated An+1BnO3n−1 perovskite blocks, the α-PbO-type[A2O2]

2+ blocks and the halide layers is possible. In fact, atransmission electron microscopy study of the Pb4BiFe4O11Cloxychloride revealed planar defects resulting from insertion ofthe [PbBiO2] slab between the hematophanite-type blocks (seeFigure 11 in ref 37). Using the tentative atomic arrangement forthe observed defect, we designed new ordered structures withthis type of intergrowth and prepared single-phase materialswith different thickness of the perovskite block, thus provingthe existence of a new [PbBiO2]An+1FenO3n−1Cl2 homologousseries. Crystal and magnetic structures of the obtainedPb5BiFe3O10Cl2 and Pb5Bi2Fe4O13Cl2 materials were inves-tigated in a wide temperature range using X-ray and neutronpowder diffraction in a combination with transmission electronmicroscopy. Magnetic properties were characterized bymagnetic susceptibility measurements and 57Fe Mossbauerspectroscopy. We also demonstrate a possibility to mix the d0

and dn cations at the B sublattice of these structures bypreparing the Ti-substituted Pb6BiFe3TiO13Cl2.

2. EXPERIMENTAL SECTIONSamples of Pb5BiFe3O10Cl2, Pb5Bi2Fe4O13Cl2 and Pb6BiFe3TiO13Cl2were synthesized by a solid-state reaction. The following precursorswere used: PbO (Sigma-Aldrich, >99.9%), PbCl2 (Aldrich, 99.98%),Bi2O3 (Aldrich, 99.99%), BiOCl, Fe2O3 (Aldrich, nanopowder with<50 nm particle size), TiO2 (Aldrich, ≥99.5%, nanopowder with≈21nm particle size). The BiOCl powder was prepared by dissolvingBi2O3 in concentrated HCl, subsequent dilution with H2O, filtrationand drying. As a bismuth precursor, for Pb5BiFe3O10Cl2 we usedBiOCl, whereas Bi2O3 was used for Pb5Bi2Fe4O13Cl2 andPb6BiFe3TiO13Cl2. Starting materials were weighed out, thoroughlyground under acetone, and pressed into pellets. At the first step thepellets were sealed in quartz ampules under dynamical vacuum of 10−4

mbar and annealed at 650 °C for 7 h. After the regrinding,Pb5BiFe3O10Cl2 was annealed at 750 °C for 20 h; Pb5Bi2Fe4O13Cl2and Pb6BiFe3TiO13Cl2 were annealed twice at 750 °C for 15 h insealed ampules.

The phase purity of the samples was verified using powder X-raydiffraction (XRD) data recorded on a Huber G670 Guinierdiffractometer (CuKα1-radiation, curved Ge(111) monochromator,transmission mode, image plate detector). The XRD patterns ofPb5BiFe3O10Cl2, Pb5Bi2Fe4O13Cl2, and Pb6BiFe3TiO13Cl2 after the LeBail fitting are shown in Figure S1 of the Supporting Information.

The chemical composition was confirmed by energy dispersive X-ray (EDX) analysis conducted on a JEOL 5510 scanning electronmicroscope equipped with an INCAx-sight 6587 system (Oxfordinstruments). The EDX spectra from 50−60 crystallites were collectedand the Pb−M, Bi−M, Fe−K, Ti−K, and Cl−K lines were used todetermine the elemental composition. Measured compositions agreewith the nominal chemical compositions within the standarddeviation:

Pb Bi Fe O Cl for Pb BiFe O Clx4.9(1) 1.0(1) 3.0(3) 2.2(3) 5 3 10 2

Pb Bi Fe O Cl for Pb Bi Fe O Clx5.0(1) 1.9(1) 3.9(3) 2.3(3) 5 2 4 13 2

Pb Bi Fe Ti O Cl for Pb BiFe TiO Clx5.7(2) 1.0(1) 3.1(3) 1.0(1) 2.1(3) 6 3 13 2

Neutron powder diffraction (NPD) data were collected on the high-resolution powder diffractometer HRPT at the Laboratory forNeutron Scattering and Imaging of the Paul Scherrer Institut (LNSPSI, Villigen, Switzerland). The data were collected at the wavelength1.8857 Å in the 2θ range 8−160°. The sample (∼12 g) was placed in avanadium container with a diameter of 10 mm. The measurementswere conducted in the temperature range from 1.5 to 700 K with astep of 50 K. The data from 1.5 to 300 K have been obtained using astandard He-cryostat. High-temperature measurements were per-formed using a custom-built tantalum radiation furnace. For themore detailed magnetic structure investigation, the NPD data for thePb5BiFe3O10Cl2 sample were collected at the cold neutron powderdiffractometer DMC (LNS PSI, Villigen, Switzerland) with thewavelength λ = 4.5082 Å at 1.5 K in a He-cryostat. The crystal andmagnetic structures were refined by the Rietveld method using theJANA2006 program.39 The symmetry analysis of possible magneticconfigurations was carried out with the ISODISTORT program.40

Electron diffraction (ED) patterns were obtained on a PhilipsCM20 transmission electron microscope (TEM) operated at 200 kV.High-angle annular dark-field scanning transmission electron micros-copy (HAADF-STEM) images and STEM-EDX elemental maps wereobtained on a FEI Titan 80−300 “cubed” microscope equipped with aSuper-X EDX detector and operated at 200 kV. The results wererecorded using the probe with a convergence semiangle of about 21mrad and a probe size of about 1 Å. The probe current rangedbetween 50 and 200 pA. For the STEM-EDX elemental maps thefollowing lines were used: Pb−L, Bi−L, Fe−K, Ti−K, O−K, and Cl−K. Samples for the TEM study were prepared by grinding the materialunder ethanol and depositing a few drops of the suspension ontocopper grids covered with a holey carbon layer. The simulatedHAADF-STEM images were calculated using the QSTEM software.41

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57Fe Mossbauer spectroscopy was performed on thePb5BiFe3O10Cl2 and Pb5Bi2Fe4O13Cl2 samples enriched with 57Fe(20% of 57Fe2O3 were used for the solid-state synthesis). Themeasurements were conducted in a transmission mode using aconstant acceleration Mossbauer spectrometer with 57Co/Rh γ-raysource. Velocities were calibrated with a standard α-Fe absorber,isomer shifts were related to α-Fe. The resulting spectra wereprocessed using UnivemMS42 and custom software.The magnetic susceptibility was measured using the vibration

sample magnetometer (VSM) setup of Quantum Design PPMS.Measurements were performed in the 10−1000 K temperature rangeand in applied fields up to 12 T. Data above 380 K were collectedusing an oven setup that operates in high vacuum (1 × 10−5 mbar). Allmeasurements were performed on heating from room temperature andon cooling back to room temperature that represents zero-field-cooling (furnace-cooling) and field-cooling regimes, respectively. Noappreciable differences between the data collected on heating andcooling were detected. Magnetic susceptibility of the spin-5/2 trilayerwas simulated using the looper quantum Monte Carlo algorithm43

from the ALPS simulation package.

3. RESULTS3.1. Crystal Structure. According to the XRD data,

Pb5BiFe3O10Cl2 and Pb5Bi2Fe4O13Cl2 samples were singlephase, whereas Pb6BiFe3TiO13Cl2 contained a small amountof an unidentified impurity producing only one reflection withthe relative intensity <1% at d = 2.29 Å. All XRD patterns wereindexed in a body-centered tetragonal unit cell with theparameters provided in Table 1.

The electron diffraction patterns of Pb5BiFe3O10Cl2 andPb5Bi2Fe4O13Cl2 are shown in Figure 2 (for the patterns ofPb6BiFe3TiO13Cl2 see Figure S2 of the Supporting Informa-tion). The reflections on these patterns meet the reflectioncondition hkl: h + k + l = 2n corresponding to a body-centeredunit cell. Very weak extra reflections hk0: h + k ≠ 2n can benoticed in the [001] ED patterns. Their intensity is graduallygrowing on going away from the center of the pattern. This

means that they originate from the first-order Laue zone, whichis closely positioned to the zero order Laue zone because of thelarge c lattice parameter. In the [310] ED patterns, the lines ofmodulated intensity propagating along the c*-direction wereobserved (Figure S3 in the Supporting Information). Theorigin of these lines will be discussed below.The crystal structures of Pb5BiFe3O10Cl2, Pb5Bi2Fe4O13Cl2,

and Pb6BiFe3TiO13Cl2 were refined by the Rietveld methodfrom NPD data collected in the temperature range of 1.5−700K. Since the contribution of the rows of modulated intensityobserved on the [310] ED patterns (Figure S3 in theSupporting Information) does not produce well-defined peakson the NPD patterns, the most symmetric I4/mmm spacegroup was chosen for the structure refinement. We constructedthe initial structure model as an ordered alternation of thehematophanite-type blocks and the [PbBiO2]-type blocks withthe α-PbO ordering. In the structure refinement the followingconsiderations were applied:(1) In Pb5BiFe3O10Cl2 and Pb6BiFe3TiO13Cl2, the Bi cations

(one atom per unit cell) share positions with Pb in the[PbBiO2] slabs, because according to the EDX spectra the Bisignal is present mainly in these slabs (Figure S4 in theSupporting Information). In Pb5Bi2Fe4O13Cl2 there are two Biatoms per unit cell and the distribution of Pb and Bi cannot beaccurately refined since they have very close neutron scatteringlengths (9.40 and 8.53 fm, respectively).44 Therefore, one Biatom was placed into the [PbBiO2] slab and the second Biatom was evenly distributed among the A positions of theperovskite block resulting in the 0.8Pb+0.2Bi occupancy.(2) In all three structures, the position of the O2 atom at the

basal square plane of the BO6 octahedra is split along the a-direction. This splitting is similar to that observed in otherhematophanite-based structures being a consequence of theBO6 octahedra rotations.(3) In Pb6BiFe3TiO13Cl2, Fe and Ti jointly occupy

octahedral and square-pyramidal positions in the structure. Feand Ti have very different neutron scattering lengths (9.45 and−3.44 fm, respectively),44 which allows refining their occupancyfactors with a high accuracy. The overall composition was fixedin accordance to the EDX analysis. At 700 K, the refinementconverged to the occupancy factors of 0.89Fe+0.11Ti at thesquare-pyramidal site (the FeTi1 position) and 0.61Fe+0.39Tiat the octahedral site (the FeTi2 position). These values wereused for the crystal structure refinement at other temperatures.The presence of Ti ions in the square-pyramidal coordinationwas additionally confirmed by atomic resolution STEM-EDXanalysis (see below).(4) Upon in situ cooling of all three materials, a broad hump

appears on the NPD profiles and its intensity gradually grows(Figure S5 in the Supporting Information). For Pb5BiFe3O10Cl2and Pb5Bi2Fe4O13Cl2 it appears below ∼600 K, forPb6BiFe3TiO13Cl2, below ∼450 K. The origin of this humpwill be discussed in the next section. For the crystal structurerefinement, the 2θ interval of the hump was eliminated.The high-temperature (700 K) NPD profiles after Rietveld

refinement are given in Figure 3. The NPD profiles at 1.5 and300 K, tables with the parameters of Rietveld refinement,fractional atomic coordinates, atomic displacement parametersand selected bond distances are provided in Figure S6 andTables S1−S6 of the Supporting Information. The room-temperature crystal structures of Pb5BiFe3O10Cl2 andPb5Bi2Fe4O13Cl2 are shown in Figure 4.

Table 1. Lattice Parameters Determined from Room-Temperature Powder XRD Data

a (Å) c (Å) V (Å3)

Pb5BiFe3O10Cl2 3.9208(3) 42.989(4) 660.9(1)Pb5Bi2Fe4O13Cl2 3.9169(4) 51.490(7) 790.0(2)Pb6BiFe3TiO13Cl2 3.9215(7) 51.184(13) 787.1(4)

Figure 2. Electron diffraction patterns of (a) Pb5BiFe3O10Cl2 and (b)Pb5Bi2Fe4O13Cl2.

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3.2. HAADF-STEM and STEM-EDX Study. HAADF-STEM images of Pb5BiFe3O10Cl2 and Pb5Bi2Fe4O13Cl2 takenalong the most informative [100] zone axis are shown in Figure5 (for the image of Pb6BiFe3TiO13Cl2, see Figure S7 in theSupporting Information). The brightest dots are attributed tothe Pb/Bi columns (ZPb = 82, ZBi = 83). They form two typesof patterns: (1) a square pattern with the spacing of ∼3.9 Åcorresponding to the positions of the A cations in theperovskite structure; (2) a chessboard pattern with doublelayers of the A-cation columns of the [PbBiO2] slabs (markedby asterisks in Figure 5). The perovskite and [PbBiO2] blocksare connected through the layers of chlorine atoms (ZCl = 17,correspond to dark stripes marked by arrowheads in Figure 5).On the HAADF-STEM images, the Fe−O columns appear as

very weak dots (ZFe = 26, ZO = 8). We used the HAADF-STEM images to confirm the crystal structure solution: thecalculated images shown as an inset in Figure 5 are in a goodagreement with the experimental ones.To confirm the presence of Ti4+ in both the octahedra and

square pyramids, we performed an atomic resolution STEM-EDX analysis. The elemental maps of Pb, Bi, Fe, Ti, O, and Cltogether with the mixed Fe/Ti map and the corresponding Feand Ti intensity profiles are given in Figure 6. The dots on theprofiles stand for the experimentally measured intensities of theFe (red dots) and Ti (green dots) signals. The intensity profilesfrom the experimental maps were fitted with a set of Gaussianfunctions using a Fityk software45 (black curves). For theanalysis, the fwhm (full width at half-maximum) of all peakswas assumed to be equal. The Ti signal at the pyramidalposition is low, but well above the noise level.Although in general all three materials have well-ordered

structures, we were able to find several crystals with planardefects. A representative image is shown in Figure 7; for moreimages, see Figure S8 in the Supporting Information. Theobserved defects correspond to the insertion of extra blocks,

Figure 3. Experimental, calculated, and difference NPD profiles ofPb5BiFe3O10Cl2, Pb5Bi2Fe4O13Cl2, and Pb6BiFe3TiO13Cl2 at 700 K (λ= 1.8857 Å). On the Pb6BiFe3TiO13Cl2 NPD pattern the peaks froman admixture phase are excluded from the refinement.

Figure 4. Crystal structure of (a) n = 3 (Pb5BiFe3O10Cl2) and (b) n =4 (Pb5Bi2Fe4O13Cl2) members of the [PbBiO2]An+1BnO3n−1Cl2homologous series. The O2 positions are split due to the disorderin the rotations of the BO6 octahedra. Orange/brown spherescorrespond to the Pb/Bi atoms, green to the Cl atoms, and blue tothe O atoms. The polyhedra are centered with the Fe cations. (c)Magnetic structure of Pb5BiFe3O10Cl2 with Fe spins alignedantiferromagnetically along the c-axis.

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whose structure resembles that of the mineral peritePbBiO2Cl.

46 The number of the consecutive perite blocksvaries from 2 to 5.3.3. Magnetic Structure. The magnetic contribution to

the NPD patterns of Pb5BiFe3O10Cl2 and Pb5Bi2Fe4O13Cl2appears below T ≈ 600 K. For the Ti-substitutedPb6BiFe3TiO13Cl2 material the lower magnetic orderingtemperature of ∼450 K was estimated. The magneticcontribution to the NPD pattern of Pb5BiFe3O10Cl2 measuredat T = 1.5 K consists of two components: magnetic Bragg peakspositioned according to the (1/2,1/2,0) propagation vector(except for the peak of unknown origin with d = 4.150 Å) and ahump (Figure S9 in the Supporting Information). The positionof this hump (maximum at d ≈ 4.5 Å) corresponds to thepropagation vector (1/2,1/2,1/2). Pb5BiFe3O10Cl2 containstwo symmetry-independent magnetic iron atoms per unit cell:Fe1 (0,0,0.0911) in the square-pyramidal position and Fe2(0,0,0) in the octahedral position. Using the (1/2,1/2,0)propagation vector, we performed a group theory symmetryanalysis of possible magnetic structures.40 Among the possible

magnetic irreducible representations (irreps), only mX2+ and

mX3+ representations are common for both iron positions. Irrep

mX2+ corresponds to the Fe spins pointed along the c-axis,

whereas in the case of the mX3+ irrep, the Fe spins lie within the

ab-plane. Both irreps give a C[A]mca magnetic group (in Belov-Neronova-Smirnova, BNS, notations47), but with differentbasis: for mX2

+ a′ = c, b′ = a + b, c′= −a + b; for mX3+ a′ = −a −

b, b′ = −c, c′ = a − b.Both models were tested in the Rietveld refinement: the

atomic coordinates were fixed in accordance to the structuralrefinement described in the previous section; the backgroundand the magnetic hump were defined manually; the profile

Figure 5. HAADF-STEM images of Pb5BiFe3O10Cl2 andPb5Bi2Fe4O13Cl2 taken along the [100] zone axis. Arrowheads indicatethe chlorine layers; asterisks indicate the [PbBiO2] slabs. The insetsshow simulated images calculated using the structural parametersrefined from the NPD data (crystals thickness was 8 nm).

Figure 6. High-resolution HAADF-STEM image of Pb6BiFe3TiO13Cl2taken along the [100] zone axis, individual Pb, Bi, Fe, Ti, O, and Clatomic resolution STEM-EDX elemental maps, Fe/Ti mixed map, andthe Fe and Ti signal intensity profiles. The dots correspond to theexperimental data, the black lines to the fitting curves. Signal of Tifrom the pyramidal positions is indicated with stars.

Figure 7. [100] HAADF-STEM image showing the defects inPb5BiFe3O10Cl2 due to insertion of the perite PbBiO2Cl blocks.Arrowheads indicate the chlorine layers, asterisks stand for the PbBiO2layers.

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parameters and the values of the Fe magnetic moments wererefined. The mX2

+ irrep provides a considerably better fit of theNPD data (Rp = 0.04, Rwp = 0.06, Figure 8) compared to the

mX3+ irrep (Rp = 0.16, Rwp = 0.26). The magnetic structure is

plotted in Figure 4c; it corresponds to the G-type AFMordering of the Fe magnetic moments oriented along the c-axis.The ordered magnetic moments at 1.5 K are 1.64 μB for theFe1 site and 0.37 μB for the Fe2 site. These values are muchsmaller than those expected for the Fe3+ cations in the high-spinstate (5 μB) and observed, for example, in hematophanite andPb4BiFe4O11Cl. We attribute this apparent lowering of theordered moments to the fact that only part of the sample ismagnetically long-range ordered.The remaining spins produce a broad hump in the NPD

pattern. Remarkably, this hump is rather symmetric, as opposedto the asymmetric 2D Warren-type scattering48 that would beexpected for decoupled magnetic slabs. Besides, the humpcannot be ascribed to purely diffuse scattering49 from short-range spin−spin correlations that should produce a muchbroader feature positioned at a different scattering angle (seethe Supporting Information). Therefore, we interpret thishump as a magnetic scattering from nanodomains of themagnetic order with the propagation vector (1/2,1/2,1/2).Indeed, an estimate using the Scherrer formula L = λ/[Δ(2θ0)cos θ], where θ0 is the position of the diffuse peak and Δ(2θ0)is the fwhm of the peak, yields the correlation length ∼23 Åthat implies spin−spin correlations far beyond nearest-neighborFe3+ ions.The magnetic susceptibility data for Pb5BiFe3O10Cl2 (see

below) show that Fe3+ spins may be weakly canted producing anet magnetic moment. However, canting is not possible withinthe chosen C[A]mca symmetry. To introduce it into the modelwe used a superposition of the mX2

+ and mX3+ irreps. The P[C]

bca magnetic space group (in BNS notation) corresponds tothe suggested model of the magnetic structure. However, itdoes not meet the reflection conditions of the experimentaldiffraction data (00l: l = 2n). More importantly, uponrefinement the magnitude and the direction of canting didnot converge to an unambiguous value; and the use of thismodel did not improve the R factors of the fit. Therefore, spin

canting (if any) is beyond the sensitivity of the powder neutronexperiment.

3.4. Mossbauer Spectroscopy. Pb5BiFe3O10Cl2 andPb5Bi2Fe4O13Cl2 were characterized by 57Fe Mossbauer spec-troscopy in the temperature range of 78−573 K. According tothe spectra shown in Figure 9a, c, at 573 K, both materials are

in the paramagnetic state. The spectra were fitted using asuperposition of two quadrupole doublets (Table S7 in theSupporting Information), both with isomer shifts (ISs) of0.17−0.19 mm/s corresponding to iron in the oxidation state+3.50 The Dn1o and Dn1p doublets were assigned to octahedral(o) and pyramidal (p) sites, respectively, according to their ISsand spectral contributions (n = 3 for Pb5BiFe3O10Cl2 and n = 4for Pb5Bi2Fe4O13Cl2). The quadrupole shifts (ΔEQ) of the Fe

3+

cation in the pyramidal sites are smaller than those of the Fe3+

cation in the octahedral sites for both compounds. ThePb5BiFe3O10Cl2 spectrum also includes a minor magneticallysplit component (Si1) corresponding to the Fe2O3 impurity.Below ∼550 K, both compounds are magnetically ordered

and the spectra consist of partially overlapped magnetically splitbroadened subspectra (Sn) and minor paramagnetic doublets(Dn) (Figure 9b, d). The spectra were fitted using super-positions of hyperfine magnetic field distributions (HFDs) incombination with discrete paramagnetic doublets and Zeemansextets. The main two subspectra, fitted as HFDs or discrete

Figure 8. Fragment of the experimental, calculated, and differenceNPD profiles for Pb5BiFe3O10Cl2 after the Rietveld refinement of themagnetic structure at T = 1.5 K. The unindexed reflection wasexcluded from the refinement.

Figure 9. 57Fe Mossbauer spectra of (a, b) Pb5BiFe3O10Cl2 and (c, d)Pb5Bi2Fe4O13Cl2 taken at 573 and 78 K.

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sextets, correspond to Fe3+ cations in octahedral and pyramidalsites: the components with higher values of the magnetichyperfine field (Hhf) and slightly higher ISs correspond tooctahedral ones (Sn1,2o), and those with smaller Hhf and ISscorespond to pyramidal ones (Sn1,2p). The HFDs wereobtained by Hesse−Rubartsch method51 assuming equal butspecific for each subspectra values of ISs and the ΔEQ for theelementary sextets. Besides, there are minor ∼6−8% signifi-cantly broadened components in the spectra, fitted forsimplicity by doublets (Dn1,2). Those minor componentspresumably arise from small or defect crystallites of the mainphases in the superparamagnetic state or/and from impurities,although there are no any additional components in theparamagnetic spectra. The spectra of Pb5BiFe3O10Cl2 contain,in addition, minor sextets of the α-Fe2O3 impurity (Si2,3).The ratio between the relative spectral areas corresponding

to the “o” and “p” doublets (at 573 K) and sextets (below 550K) is in a very good agreement with the relative amount of Fe3+

in the octahedral and pyramidal coordination for bothcompounds (2:1 for Pb5BiFe3O10Cl2 and 1:1 inPb5Bi2Fe4O13Cl2).As one can see from Table S7 in the Supporting Information,

the ISs and Hhf of Fe3+ cations in octahedral and pyramidal

coordination at the same temperature for both compounds arerather similar to each other. The corresponding apparentquadrupole shifts ΔEQ of Fe3+ in octahedral sites are alsosimilar, while those of Fe3+ in pyramidal coordination are of theopposite sign. The latter reflects the difference in localdistortions of the pyramidal coordination of Fe inPb5BiFe3O10Cl2 and Pb5Bi2Fe4O13Cl2. This difference in thelocal distortion can be attributed to a different surrounding ofthe FeO5 pyramids by the Pb and Bi cations at the Pb1 and Pb2positions. In the Pb5BiFe3O10Cl2 structure, the Pb1 and Pb2positions are occupied by the Pb atoms only, whereas for thePb5Bi2Fe4O13Cl2 structure the mixed 0.8Pb+0.2Bi occupation issuggested. The temperature dependences of Hhf for octahedraland pyramidal sublattices in both compounds are shown inFigure S10 of the Supporting Information. By fitting theexperimental data with the power equation of Hhf(T) = B1(1 −T/TN)

γ, where B1 = Hhf(0)D, the static critical exponent γ andNeel temperature TN were evaluated. The obtained values of γ≈ 0.3−0.4 are consistent with a 3D universality class.52 The Hhfvalues of ∼53 and 51 T at 78 K in the octahedral and pyramidalpositions are also close to those reported for the high-spin Fe3+

cations in antiferromagnetic oxides and oxide-fluorides.50,53

The TN values were estimated as ∼540−550 K, which issomewhat lower than the temperature where magnetic diffuseintensity in the NPD patterns vanishes. Comparison of theobtained Mossbauer parameters of Pb5BiFe3O10Cl2 with thoseof the hematophanite Pb4Fe3O8Cl

54 reveals their closeresemblance. Hematophanite is magnetically ordered below600 K forming the long-range ordered 3D AFM structure withthe magnetic moment of the Fe3+ of 3.94 μB.

32

Remarkably, Mossbauer spectroscopy as a local probe doesnot distinguish between the Fe3+ magnetic moments producingsharp neutron reflections and diffuse scattering. This indicatesthat the same G-type antiferromagnetic order developsthroughout the whole crystal, but ordered domains of differentsize are formed.3.5. Magnetic Susceptibility. The magnetic susceptibility

of Pb5BiFe3O10Cl2 reveals the formation of a weak net momentbelow 600 K (Figure 10, top). This is typical for cantedantiferromagnets, where weak noncollinearity of the magnetic

structure introduces an uncompensated magnetic moment. Thesize of the net moment is about 0.03 μB/f.u. at 5 K. In Fe3+

oxides, similar effects are often caused by ferro- or ferrimagneticimpurities. However, in our case the transition temperature ofabout 600 K does not match that of Fe2O3 (950 K), Fe3O4(858 K), and PbFe12O19-type hexaferrites (620−640 Kdepending on the composition). On the other hand, it matchesthe onset temperature of the magnetic scattering in neutrondiffraction patterns, and it is only slightly above the temperaturewhere hyperfine splitting of the Mossbauer spectra appears.Additionally, we confirmed the intrinsic nature of the 600 Ktransition by measuring the magnetic susceptibility of twodifferent samples of Pb5BiFe3O10Cl2. Both samples showed thesame transition temperature and the same size of the netmoment.Above 600 K, the magnetic susceptibility of Pb5BiFe3O10Cl2

does not change monotonically. A broad maximum seenaround 800 K signifies low-dimensional magnetism ofindividual trilayers of Fe3+ ions. Indeed, the data are well-described by the model of a single trilayer (Figure 10, top,inset), where for simplicity we chose same interaction energy Jwithin the planes and between the planes of the trilayer. The fitto the experimental data yields J = 75 K, which is comparable tothe antiferromagnetic exchange interaction in systems withnearly 180 ° Fe3+−O−Fe3+ superexchange, such as LaFeO3 (J =58 K)55 and LaSrFeO4 (J = 86 K).56

The magnetic behavior of Pb6BiFe3TiO13Cl2 is similar to thatof Pb5BiFe3O10Cl2 (Figure 10, middle). The magnetictransition is seen around 400 K in reasonable agreement withthe transition temperature of 450 K expected from neutron

Figure 10. Magnetic susceptibility of Pb5BiFe3O10Cl2 (top),Pb6BiFe3TiO13Cl2 (middle), and Pb5Bi2Fe4O13Cl2 (bottom). Thearrows mark transition temperatures. The inset in the top panelmagnifies the broad maximum of the susceptibility above 600 K andadditionally shows the fit with the spin-5/2 trilayer model, as describedin the text.

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diffraction. The net moment is about 0.03 μB/f.u. at 5 K. Above400 K, the susceptibility decreases with increasing temperature.No signatures of low-dimensional magnetism were observed.This is probably due to trace amounts of a ferromagneticimpurity that causes weak field dependence of the susceptibilityeven above 400 K and conceals the intrinsic signal.Finally, Pb5Bi2Fe4O13Cl2 shows a very different magnetic

behavior (Figure 10, bottom). The susceptibility of thiscompound is at least 10 times lower than that of the othertwo, and no signatures of the net moment could be seen at lowtemperatures. In fact, the susceptibility shows a different trendand even increases slightly when the field is increased. This maybe due to a spin-flop transition in the antiferromagneticallyordered state, whereas above TN ≈ 580 K the curves nearlymerge. A weak kink of the susceptibility is compatible with theonset of the long-range order in this temperature range. Note,however, that the Pb5Bi2Fe4O13Cl2 sample turned out to berather unstable at high temperatures in high vacuum. Therefore,no reliable data above 650 K could be obtained.

4. DISCUSSIONWe prepared two intergrowth structures, Pb5BiFe3O10Cl2 andPb5Bi2Fe4O13Cl2, that can be regarded as the n = 3 and n = 4members of a new homologous series [PbBiO2]-An+1FenO3n−1Cl2 (A = Pb/Bi). These structures are a sequenceof the following blocks: − [An+1FenO3n−1 − Cl − PbBiO2 − Cl− An+1FenO3n−1 − Cl − PbBiO2 − Cl] −, and can be formallyconsidered as an intergrowth of the hematophanite and Sillen-type structures. An+1FenO3n−1 is a truncated perovskite block,where one (n = 3) or two (n = 4) octahedral layers aresandwiched between the square-pyramidal layers. There arefour Cl layer and two [PbBiO2] slabs in a unit cell. Each Cllayer forms a CsCl-type A2Cl ordering with the adjacent Pb/Bilayer of the [PbBiO2] slab and the A layer of the perovskiteblock. The [PbBiO2] slab has an α-PbO type structure. Thepossibility to replace the Fe3+ cations in the perovskiteAn+1FenO3n−1 block with the d0 transition-metal cation (Ti4+)has been demonstrated by preparing the Pb6BiFe3TiO13Cl2material, where the charge balance is maintained bysimultaneous Bi3+ → Pb2+ substitution in the A sublattice.The [PbBiO2]An+1BnO3n−1Cl2 structures have much in

common with the hematophanite-based homologous seriesAn+1BnO3n−1Cl

32,37,38 (Figure 1d). For comparison, we willconsider the room-temperature structures in both series andanalyze the interatomic distances, B-cation distribution,octahedral rotation patterns, and magnetic ordering.Interatomic Distances. The distortion of B−O polyhedra

in the An+1BnO3n−1Cl and [PbBiO2]An+1BnO3n−1Cl2 structures isillustrated in Figure 11. The distortion of the BO5 squarepyramids is very similar in all the structures: the distance to theapical oxygen (B1−O3) is short (1.82−1.88 Å) and thedistance to the basal oxygen atoms (B1−O1) is longer (2.02−2.05 Å). In the n = 3 structures (Pb4Fe3O8Cl

32 andPb5BiFe3O10Cl2), the octahedra are rather symmetric: the Bcation stays at the center with the basal B2−O2 bond length of2.00 Å and apical B2−O3 bond length of 2.04 Å. In the n = 4members, the octahedra are more distorted. The B cationsdisplace from the center of the octahedra along the c-axis,leading to one short (B2−O4, ∼1.96−2.00 Å) and one long(B2−O3, ∼2.06−2.20 Å) distances. In both homologous series,the bond valence sum (BVS)57 values calculated for the ironatoms in the octahedral B2 and pyramidal B1 positions areconsiderably different being in the range of ∼3.0−3.1 and

∼2.6−2.7 for the B2 and B1 positions, respectively. The Pb−Cldistances are very close in both homologous series (3.26−3.34Å).

Ti4+ in Square Pyramids. From the NPD data, we foundthat Fe3+ and Ti4+ ions in Pb6BiFe3TiO13Cl2 are partiallyordered with the occupancy of 0.89Fe+0.11Ti at the square-pyramidal site (the FeTi1 position) and 0.61Fe+0.39Ti at theoctahedral site (the FeTi2 position). This is exactly the samedistribution which was observed in Pb5Fe3TiO11Cl.

38 In bothcases, the presence of a small amount of titanium in squarepyramids was confirmed by the STEM-EDX analysis. There areonly few more examples of the structures where Ti4+ cationshave 5-fold coordination environment: mineral fresnoite(Ba2TiSi2O8)

58 and few related compounds (Sr2TiSi2O8,Ba2TiGe2O8,

59 Na4Ti2Si8O22·4H2O60), metatitanates of alkaline

metals (MNaTiO3, where M = K,61 Rb, or Cs62), andSm2TiO5.

63

Octahedra Rotation. Similar to the structures of thehematophanite An+1BnO3n−1Cl homologous series, the BO6octahedra in the [PbBiO2]An+1BnO3n‑1Cl2 structures tend torotate cooperatively about the c-axis. The I4/mmm space groupdoes not imply octahedral rotation, but the presence of themodulated intensity lines parallel to the c*-direction on the[310] ED patterns (Figure S3 in the Supporting Information)indicates certain ordered stacking sequences of rotatedoctahedra within the perovskite blocks as well as between theperovskite blocks, which however lack a perfect long-rangeorder. Enlarged fragments of the lines are shown in Figure 12for Pb5BiFe3O10Cl2 (a), Pb5Bi2Fe4O13Cl2 (b), andPb6BiFe3TiO13Cl2 (c). One can notice that the intensitydistribution is very different for the three structures.There is only one octahedral layer in Pb5BiFe3O10Cl2 and the

presence of the spots on the ED pattern indicates that theordering occurs between the consecutive perovskite blocksalong the c-direction. However, crystals with different patterns

Figure 11. B−O interatomic distances in the square pyramids andoctahedra in six structures: members of the An+1BnO3n−1Cl series, n = 3(Pb4Fe3O8Cl

32) and n = 4 (Pb4BiFe4O11Cl37 and Pb5Fe3TiO11Cl

38),and members of the [PbBiO2]An+1BnO3n−1Cl2 series, n = 3(Pb5B iFe3O10Cl 2) and n = 4 (Pb5B i 2Fe4O13Cl 2 andPb6BiFe3TiO13Cl2). In the pyramids, there are two B−O distances:one short apical B1−O3 distance and four long basal B1−O1distances. In the octahedra, there are four basal B2−O2 bonds and twoapical bonds (in the n = 3 structures, the apical bonds are equivalentby symmetry, whereas in the n = 4 members, they are different).

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of the satellite reflections were found (four examples are shownin Figure 12a), which demonstrates that the ordering occurs ona local scale and is not homogeneous throughout the material.In the Pb5Bi2Fe4O13Cl2 and Pb6BiFe3TiO13Cl2 structures, thereare two octahedral layers in the perovskite block, and theintensity distribution within the lines on the [310] ED patternsare determined by the mutual rotation of the octahedra in theselayers (in-phase or out-of-phase). The intensity distribution inPb5Bi2Fe4O13Cl2 (Figure 12b) strongly resembles the EDpattern of Pb4BiFe4O11Cl,

37 which corresponds to theprevalence of the in-phase octahedra rotation in the perovskiteblocks. The pattern of Pb6BiFe3TiO13Cl2 (Figure 12c)resembles the ED pattern of Pb5Fe3TiO11Cl,

38 whichcorresponds to the out-of-phase rotation. The detailedinterpretation of the ED patterns related to different tiltsystems is provided in refs 37 and 38.The amplitudes of the BO6 octahedra rotation in the

[PbBiO2]An+1BnO3n‑1Cl2 structures are similar to those in theAn+1BnO3n−1Cl compounds. The n = 3 members in both seriesdemonstrate the highest degree of octahedra rotation: ∼12° at1.5 K and ∼10° at 700 K (calculated from the splitting of theO2 position). The octahedra rotation in the n = 4 memberswith B = Fe/Ti is the smallest: with ∼7−8° at 1.5 K and ∼3−4°at 700 K. The values for the n = 4 members with B = Fe areintermediate: ∼6−8° at 1.5 K and ∼5−8° at 700 K.Magnetic Ordering. Similar to the members of the

hematophanite-based series, the magnetic ordering of the[PbBiO2]An+1BnO3n−1Cl2 compounds is antiferromagnetic of G-type. The values of the Neel temperatures are close as well andhover around 600 K in both series, whereas the dilution of theFe sublattice with Ti reduces TN down to 400−450 K inPb5Fe3TiO11Cl and Pb6BiFe3TiO13Cl2. From the structuralperspective, one expects that the large spatial separationbetween the magnetic slabs impedes 3D magnetic order andintroduces 2D magnetism that we indeed observed inPb5BiFe3O10Cl2 above 600 K (Figure 10, top). However,even the very large separation of nearly 14 Å between themagnetic slabs in this compound has only weak effect on TN. Infact, TN depends on log(J⊥/J), where J is the (effective)coupling within the magnetic slab, and J⊥ is the couplingbetween the slabs.64 This feature is advantageous for materialsdesign, because large nonmagnetic units introduced between

magnetic slabs do not prevent the magnetic order, which iscrucial for applications such as multiferroics.The mechanism behind the 3D order in the [PbBiO2]-

An+1BnO3n−1Cl2 series is likely to be different from the one inhematophanite and related compounds. The structure ofhematophanite entails one magnetic slab per unit cell, so thatthe two contiguous slabs are always on top of each other. Then,the leading interaction between the slabs is antiferromagneticand runs along the c-direction between one Fe3+ ion in the toplayer of one slab and one Fe3+ ion in the bottom layer of theneighboring slab. This explains why hematophanite with threelayers of Fe3+ ions per slab develops a doubled magnetic unitcell along the c-direction (propagation vector (1/2,1/2,1/2)),whereas in Pb4BiFe4O11Cl with four layers of Fe3+ ions per slabthe crystal and magnetic structures have the same periodicityalong the c-axis (propagation vector (1/2,1/2,0)).The case of the [PbBiO2]An+1BnO3n−1Cl2 series is more

complex. These structures have two magnetic slabs per unit cell,and the body-centering symmetry requires that the adjacentslabs are shifted over half of the ab diagonal. Therefore, eachFe3+ ion in the top layer of one slab interacts with four Fe3+

ions in the bottom layer of the neighboring slab. Given theAFM order in the ab plane, this Fe3+ ion would be coupled totwo spin-up and two spin-down Fe3+ ions, hence the overallinterlayer interaction cancels. This situation is typical forK2NiF4-type compounds, where neighboring magnetic layersare also shifted over half of the diagonal in the ab plane. The3D magnetic order is then stabilized by weak dipolarinteractions that are, however, fragile and sensitive to detailsof the crystal structure. For example, the doubled periodicityalong c (propagation vector (1/2,1/2,1/2)) is primarilystabilized in Ca2MnO4,

65 while the shorter periodicity withthe propagation vector (1/2,1/2,0) has been reported forK2NiF4.

66 Sometimes both types of magnetic order are presentsimultaneously, as in Rb2MnF4,

66 or vary from sample tosample depending on the preparation procedure, as inRb2MnCl4.

67

In Pb5BiFe3O10Cl2, the (1/2,1/2,0) magnetic order resem-bles that in K2NiF4, whereas the broad hump can be ascribed tothe competing (1/2,1/2,1/2) order, as in Rb2MnF4. Surpris-ingly, two types of magnetic order have very differentcorrelation lengths, with the (1/2,1/2,1/2) order formingnanodomains having the average size of 23 Å only. Thestabilization of different magnetic structures in different regionsof the crystal may be related to structural defects affecting weakdipolar couplings that decide whether the (1/2,1/2,0) or (1/2,1/2,1/2) order is formed.Additionally, our magnetization data (Figure 10) suggest

weak spin canting that should be induced by the in-plane two-site anisotropy of Dzyaloshinsky-Moriya (DM) type. This DMinteraction will not be allowed by symmetry in the idealized I4/mmm structure. However, the real symmetry is lower becauseof the rotations of octahedra. These rotations eliminateinversion centers between the Fe3+ sites in the ab plane andfacilitate DM couplings similar to LaFeO3 and other distortedperovskites.68

Altogether, we argue that complex intergrowth structuresmay be detrimental for the 3D magnetic order. While largenonmagnetic units have only a weak effect on the Neeltemperature, the displacement of magnetic slabs in body-centered crystal structures cancels exchange interactionsbetween the slabs and gives way to weaker effects such asdipolar interactions that may be robust in simple structures of

Figure 12. Enlarged fragments of the experimental ED patterns takenalong the [310] zone: (a) four different crystals of Pb5BiFe3O10Cl2;(b) Pb5Bi2Fe4O13Cl2; (c) Pb6BiFe3TiO13Cl2. The circle indicates theposition of the central beam (000) on the ED patterns.

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K2NiF4 type, but less efficient in complex intergrowthstructures with intrinsic disorder. The fragmentation of the3D magnetic order into domains of few nm size is stillacceptable for applications because net magnetic moments arepresent in Pb5BiFe3O10Cl2 and Pb6BiFe3TiO13Cl2, seeminglyundisturbed by the small domain size. Nevertheless, a naturalway to work around the problem of small domains would bethe search for intergrowth structures, where neighboring slabsare on top of each other, and the 3D magnetic order is drivenby the direct exchange interaction along the c-axis, similar tohematophanite and related compounds.

■ CONCLUSIONS

We established the existence of a new [PbBiO2]An+1BnO3n‑1Cl2homologous series based on intergrowth of the hematophaniteand Sillen-type structures and prepared the n = 3(Pb5BiFe3O10Cl2) and n = 4 (Pb5Bi2Fe4O13Cl2 andPb6BiFe3TiO13Cl2) members. The crystal structures of thesehomologues are built from a stacking of truncated An+1BnO3n−1perovskite blocks, α-PbO-type [A2O2]

2+ (A = Pb, Bi) block andhalide layers. The perovskite block consists of one (n = 3) ortwo (n = 4) octahedral slabs sandwiched between layers of BO5square pyramids. The [PbBiO2]An+1BnO3n−1Cl2 compoundsdevelop a magnetically ordered state below ∼600 K(Pb5BiFe3O10Cl2 and Pb5Bi2Fe4O13Cl2) and ∼450 K(Pb6BiFe3TiO13Cl2) with the G-type AFM ordering of the Fespins aligned along the c-axis. However, neutron diffractionindicates the coexistence of conventional long-range magneticorder and tiny ordered domains with the size of few nm.

■ ASSOCIATED CONTENT

*S Supporting InformationTables with NPD experimental details, atomic parameters,selected interatomic distances, and 57Fe Mossbauer parametersfor Pb5BiFe3O10Cl2, Pb5Bi2Fe4O13Cl2, and Pb6BiFe3TiO13Cl2.Room-temperature XRD profiles; additional electron diffractionpatterns and HAADF-STEM images; NPD profiles at differenttemperatures; M(H) curves. This material is available free ofcharge via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATION

Corresponding Author*E-mail: maria.batuk@uantwerpen.be.

Author ContributionsAll authors have given approval to the final version of themanuscript.

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTS

A.M.A. and D.S.F. are grateful to the Russian ScienceFoundation for the financial support (grant 14-13-00680).A.A.T was funded by the Mobilitas grant of the ESF (MTT77)and by the IUT23-3 grant of the Estonian Research Agency.M.F. received funding from the European Community’sSeventh Framework Programme (FP7/2007-2013) underGrant 290605 (PSIFELLOW/COFUND). This work ispartially based on experiments performed at the Swissspallation neutron source SINQ, Paul Scherrer Institut (PSI),Villigen, Switzerland.

■ REFERENCES(1) Hervoches, C. H.; Lightfoot, P. Chem. Mater. 1999, 11, 3359−3364.(2) Hervoches, C. H.; Snedden, A.; Riggs, R.; Kilcoyne, S. H.;Manuel, P.; Lightfoot, P. J. Solid State Chem. 2002, 164, 280−291.(3) Frit, B.; Mercurio, J. P. J. Alloys Compd. 1992, 188, 27−35.(4) Charkin, D. O. Russ. J. Inorg. Chem. 2008, 53, 1977−1996.(5) Kusainova, A. M.; Lightfoot, P.; Zhou, W.; Stefanovich, S. Y.;Mosunov, A. V.; Dolgikh, V. A. Chem. Mater. 2001, 13, 4731−4737.(6) Kusainova, A. M.; Zhou, W.; Irvine, J. T. S.; Lightfoot, P. J. SolidState Chem. 2002, 166, 148−157.(7) Kusainova, A. M.; Stefanovich, S. Y.; Irvine, J. T. S.; Lightfoot, P.J. Mater. Chem. 2002, 12, 3413−3418.(8) Avila-Brande, D.; Gomez-Herrero, A.; Landa-Canovas, A. R.;Otero-Díaz, L. C. Solid State Sci. 2005, 7, 486−496.(9) Liu, S.; Blanchard, P. E. R.; Avdeev, M.; Kennedy, B. J.; Ling, C.D. J. Solid State Chem. 2013, 205, 165−170.(10) Avila-Brande, D.; Landa-Canovas, A. R.; Otero-Díaz, L. C. ActaCrystallogr., Sect. B 2008, 64, 438−447.(11) Avila-Brande, D.; Otero-Díaz, L. C.; Landa-Canovas, A. R.; Bals,S.; Van Tendeloo, G. Eur. J. Inorg. Chem. 2006, 2006, 1853−1858.(12) Liu, S.; Miiller, W.; Liu, Y.; Avdeev, M.; Ling, C. D. Chem.Mater. 2012, 24, 3932−3942.(13) Giddings, A. T.; Stennett, M. C.; Reid, D. P.; McCabe, E. E.;Greaves, C.; Hyatt, N. C. J. Solid State Chem. 2011, 184, 252−263.(14) Tsujimoto, Y.; Yamaura, K.; Uchikoshi, T. Inorg. Chem. 2013,52, 10211−10216.(15) McGlothlin, N.; Ho, D.; Cava, R. J. Mater. Res. Bull. 2000, 35,1035−1043.(16) Knee, C. S.; Price, D.; Lees, M.; Weller, M. Phys. Rev. B 2003,68, 174407.(17) Knee, C. S.; Weller, M. T. J. Solid State Chem. 2002, 168, 1−4.(18) Knee, C. S.; Zhukov, A. A.; Weller, M. T. Chem. Mater. 2002,14, 4249−4255.(19) Knee, C. S.; Weller, M. T. Chem. Commun. 2002, 5, 256−257.(20) Ackerman, J. F. J. Solid State Chem. 1991, 92, 496−513.(21) Dixon, E.; Hayward, M. A. Inorg. Chem. 2010, 49, 9649−9654.(22) Knee, C. S.; Field, M. A. L.; Weller, M. T. Solid State Sci. 2004,6, 443−450.(23) Romero, F. D.; Hayward, M. A. Inorg. Chem. 2012, 51, 5325−5331.(24) Yang, T.; Sun, J.; Croft, M.; Nowik, I.; Ignatov, A.; Cong, R.;Greenblatt, M. J. Solid State Chem. 2010, 183, 1215−1220.(25) Li, R. Inorg. Chem. 1997, 36, 4895−4896.(26) Rouse, R. C. Am. Mineral. 1971, 56, 625−627.(27) Pannetier, J.; Batail, P. J. Solid State Chem. 1981, 39, 15−21.(28) Cava, R. J.; Bordet, P.; Capponi, J. J.; Chaillout, C.; Chenavas, J.;Fournier, T.; Hewat, E. A.; Hodeau, J. L.; Levy, J. P.; Marezio, M.;Batlogg, B.; Rupp, L. W. Phys. C Supercond. 1990, 167, 67−74.(29) Li, R. J. Solid State Chem. 1997, 130, 154−156.(30) Li, R. Phys. C Supercond. 1997, 277, 252−256.(31) Crooks, R. J.; Knee, C. S.; Weller, M. T. Chem. Mater. 1998, 10,4169−4172.(32) Knee, C. S.; Weller, M. T. J. Mater. Chem. 2001, 11, 2350−2357.(33) Hyatt, N. C.; Hriljac, J. A. Phys. C Supercond. 2002, 366, 283−290.(34) Mclaughlin, A. C.; McAllister, J. A.; Stout, L. D.; Attfield, J. P.Solid State Sci. 2002, 4, 431−436.(35) Mclaughlin, A. C.; McAllister, J. A.; Stout, L. D.; Attfield, J. P.Phys. Rev. B 2002, 65, 8−11.(36) Mclaughlin, A. C.; Attfield, J. P.; Liu, R. S.; Jang, L.-Y.; Zhou, W.Z. J. Solid State Chem. 2004, 177, 834−838.(37) Batuk, M.; Batuk, D.; Tsirlin, A. A.; Rozova, M. G.; Antipov, E.V.; Hadermann, J.; Van Tendeloo, G. Inorg. Chem. 2013, 52, 2208−2218.(38) Batuk, M.; Batuk, D.; Abakumov, A. M.; Hadermann, J. J. SolidState Chem. 2014, 215, 245−252.(39) Petrícek, V.; Dusek, M.; Palatinus, L. Z. Krist.−Cryst. Mater.2014, 229, 345−352.

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(40) Campbell, B. J.; Stokes, H. T.; Tanner, D. E.; Hatch, D. M. J.Appl. Crystallogr. 2006, 39, 607−614.(41) Koch, C. Determination of core structureperiodicity and pointdefect density along dislocations. PhD Thesis, Arizona State University,Tempe, AZ, 2002.(42) Bruggemann, S. A.; Artzybashev, Y. A.; Orlov, S. V. UNIVEM,version 4.5; 1993.(43) Todo, S.; Kato, K. Phys. Rev. Lett. 2001, 87, 047203.(44) Sears, V. F. Neutron News 1992, 3, 26−37.(45) Wojdyr, M. J. Appl. Crystallogr. 2010, 43, 1126−1128.(46) Gillberg, M. Ark. Mineral. Geol. 1960, 2, 565−570.(47) Belov, N. V.; Neronova, N. N.; Smirnova, T. S. Acta Crystallogr.1957, 10, 848.(48) Warren, B. Phys. Rev. 1941, 59, 693−698.(49) Nilsen, G. J.; Coomer, F. C.; De Vries, M. A.; Stewart, J. R.;Deen, P. P.; Harrison, A.; Rønnow, H. M. Phys. Rev. B: Condens. MatterMater. Phys. 2011, 84, 172401.(50) Menil, F. J. Phys. Chem. Solids 1985, 46, 763−789.(51) Hesse, J.; Rubartsch, A. J. Phys. E 1974, 7, 526−532.(52) Thomas, M. F.; Johnson, C. E. In Mossbauer Spectroscopy;Dickson, D. D. E., Berry, F. J., Eds.; Cambridge University Press:Cambridge, 1986.(53) Hancock, C. A.; Herranz, T.; Marco, J. F.; Berry, F. J.; Slater, P.R. J. Solid State Chem. 2012, 186, 195−203.(54) Emery, J.; Cereze, A.; Varret, F. J. Phys. Chem. Solids 1980, 41,1035−1040.(55) McQueeney, R.; Yan, J.-Q.; Chang, S.; Ma, J. Phys. Rev. B 2008,78, 184417.(56) Qureshi, N.; Ulbrich, H.; Sidis, Y.; Cousson, A.; Braden, M.Phys. Rev. B 2013, 87, 054433.(57) Brown, I. D.; Altermatt, D. Acta Crystallogr., Sect. B 1985, 41,244−247.(58) Moore, P. B.; Louisnathan, J. Science 1967, 156, 1361−1362.(59) Hoche, T.; Russel, C.; Neumann, W. Solid State Commun. 1999,110, 651−656.(60) Roberts, M. A.; Sankar, G.; Thomas, J. M.; Jones, R. H.; Du, H.;Chen, J.; Pang, W.; Xu, R. Nature 1996, 381, 401−404.(61) Werthmann, R.; Hoppe, R. Z. Anorg. Allg. Chem. 1985, 523, 54−62.(62) Weiss, C.; Hoppe, R. Z. Anorg. Allg. Chem. 1995, 621, 1447−1453.(63) Aughterson, R. D.; Lumpkin, G. R.; Reyes, M. D. L.; Sharma,N.; Ling, C. D.; Gault, B.; Smith, K. L.; Avdeev, M.; Cairney, J. M. J.Solid State Chem. 2014, 213, 182−192.(64) Yasuda, C.; Todo, S.; Hukushima, K.; Alet, F.; Keller, M.;Troyer, M.; Takayama, H. Phys. Rev. Lett. 2005, 94, 217201.(65) Cox, D.; Shirane, G.; Birgeneau, R.; MacChesney, J. Phys. Rev.1969, 188, 930−932.(66) Birgeneau, R.; Guggenheim, H.; Shirane, G. Phys. Rev. B 1970, 1,2211−2230.(67) Gurewitz, E.; Epstein, A.; Makovsky, J.; Shaked, H. Phys. Rev.Lett. 1970, 25, 1713−1714.(68) Kim, B. H.; Min, B. I. New J. Phys. 2011, 13, 073034.

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DOI: 10.1021/acs.chemmater.5b00233Chem. Mater. XXXX, XXX, XXX−XXX

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