Ba2F2Fe1.5Se3: An Intergrowth Compound Containing Iron Selenide

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Ba2F2Fe1.5Se3: An Intergrowth Compound Containing Iron Selenide Layers Dalel Driss, Etienne Janod, Benoit Corraze, Catherine Guillot-Deudon, and Laurent Cario* Institut des Matériaux Jean Rouxel, CNRS, Université de Nantes, 2 rue de la Houssinière, BP3229, 44322 Nantes, France S Supporting Information *

ABSTRACT: The iron selenide compound Ba2F2Fe1.5Se3 was synthesized by a high-temperature ceramic method. The single-crystal X-ray structure determination revealed a layered-like structure built on [Ba2F2]2+ layers of the fluorite type and iron selenide layers [Fe1.5Se3]2−. These [Fe1.5Se3]2− layers contain iron in two valence states, namely, FeII+ and FeIII+ located in octahedral and tetrahedral sites, respectively. Magnetic measurements are consistent with a high-spin state for FeII+ and an intermediate-spin state for FeIII+. Moreover, susceptibility and resistivity measurements demonstrate that Ba2F2Fe1.5Se3 is an antiferromagnetic insulator.

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glovebox to avoid any contact of the reactants with air. The mixture was then heated to 675 °C for 72 h (50 °C/h) and then cooled to room temperature (100 °C/h). In order to obtain an almost pure sample, several regrinding and reheating steps were performed at 675 °C using the same conditions. Finally, a heat treatment at 1000 °C was used to grow single crystals by congruently melting the powder of Ba2F2Fe1.5Se3. Chemical Analysis. Several crystals were analyzed by energydispersive X-ray spectroscopy using a JEOL 5800LV scanning electron microscope. These analyses revealed that the crystals are constituted of Ba, Fe, Se, and F elements. Fluorine was detected, but its low atomic number prevented its accurate quantification. The proportions 29.7%, 22.7%, and 47.5% were found for Ba, Fe, and Se, respectively. These values are in very good agreement with the 30.8%, 23.1%, and 46.1% values calculated respectively for Ba, Fe, and Se using the formulation Ba2F2Fe1.5Se3. Single-Crystal X-ray Diffraction. Single-crystal X-ray diffraction was performed on a Kappa-Nonius CCD diffractometer equipped with Mo Kα radiation (λ = 0.71073 Å). A total of 414 frames were collected at room temperature using the ϕ and ω scan modes and a crystal-todetector distance of 27.3 mm. The rotation was 1.4°/frame, and the time of exposure was equal to 42 s/frame. A total of 36840 reflections were collected. All reflections were corrected from absorption effects using the Gaussian method and the crystal shape and dimensions. Moreover, the Lorentz and polarization effects were also corrected. The set of collected reflections was consistent with an orthorhombic symmetry with cell parameters a = 12.9428(2) Å, b = 19.2210(5) Å, and c = 6.3286(8) Å. The data were then averaged using the point group mmm. This averaging led, with a satisfying Rint of 7.7%, to a set of 3522 unique reflections. Finally, analyses of systematic absences suggested the space group Pnma. All data treatments and calculations were carried out with the Jana 2006 software.21 The structural model was first obtained thanks to direct methods. The structure was then refined by a full-matrix leastsquares method based on F2. All atoms except F were refined with anisotropic displacement parameters, and the structures converged with satisfying reliability factors Robs = 0.0295 and Rwobs = 0.0555 for

INTRODUCTION Numerous oxypnictides,1−4 oxychalcogenides,5−10 and fluorochalcogenides,11−13 containing a rare-earth or an alkalineearth transition metal, show layered-type intergrowth structures. These mixed-anion compounds are generally built on an alternating stacking of two types of layers containing different anions. Since the discovery of high-TC superconductivity in the oxypnictide LaOFeAs,1 these types of compounds have been the subject of tremendous research, and new iron arsenide intergrowth compounds were discovered.3,4,14 In the meantime, the α-FeSe, 15 K x Fe 2 Se 2 , 16 K 0.3 Fe 2 Se 2 (NH 3 ) 0.47 , 17 and Lix(NH2)y(NH3)1−yFe2Se2 (x ∼ 0.6; y ∼ 0.2)18 chalcogenide compounds that exhibit a layered structure containing antifluorite sheets Fe2Se2 were also studied and found to be superconductors with critical temperatures as high as 44 K. This critical temperature was even raised recently above 100 K in a single FeSe layer.19 The presence of superconductivity in binary and ternary iron selenide pushes therefore for an investigation of mixed-anion intergrowth compounds containing iron selenide layers. This work reports on the discovery and study of the new mixed-anion intergrowth compound Ba2F 2Fe1.5Se3. The structure determination by means of X-ray diffraction on a single crystal revealed a layered structure isotypic of the sulfide compound Ba2F2Fe1.5S3.20 Bond valence calculations as well as Mössbauer measurements confirm a mixed valence of iron, while the magnetic and transport studies show that this compound is an antiferromagnetic (AFM) insulator.

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EXPERIMENTAL METHODS

Synthesis. Ba2F2Fe1.5Se3 was synthesized by a high-temperature ceramic method. The starting reactants, BaF2 and Ba, Fe, and Se powders, were mixed and ground together in an agate mortar, in a ratio of 1:1:1.5:3. The Ba powder of a few hundred micron grain size was prepared just before use by scratching with a file a metallic barium ingot. The mixture was then placed in a carbonized silica tube, which was evacuated and flame-sealed. All preparations were performed in a © XXXX American Chemical Society

Received: December 7, 2015

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DOI: 10.1021/acs.inorgchem.5b02662 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry 2014 observed reflections [I > 3σ(I)] and 76 parameters. Data collection and refinement information are given in Table 1.

Table 1. Crystallographic Information and Results of SingleCrystal X-ray Structure Refinement for Ba2F2Fe1.5Se3 Crystallographic and Physical Data Ba2F2Fe1.5Se3 633.3 orthorhombic black Pnma 12.9428(2) 19.221(5) 6.3286(8) 1574.4(5) 8 5.3439 113 × 117 × 28 Data Collection and Reduction temperature (K) 293 wavelength (Å) 0.71069 F(000) 2168 angular range θ (deg) 6.41−34.99 h, k, l ranges −18 < h < +20; −30 < k < +30; −10 < l < +6 collected reflns 36840 indep reflns 3522 obsd reflns [I > 3σ(I)] 2014 abs corr Gaussian abs coeff (mm−1) 26.407 Rint (all reflns) 0.0770 Tmin/Tmax 0.0706/0.4586 Structural Refinement refinement method least squares on F2 F(000) 2168 data/restrictions/param 3522/0/76 reliability factors Robs = 0.0290; Rall = 0.0739 weighted reliability factors Rwobs = 0.0555; Rwall = 0.0706 S 1.62 residual electronic density 2.88/−2.76 (e/Å3) chemical formulation molar mass (g/mol) symmetry color space group a (Å) b (Å) c (Å) volume (Å3) Z density (g/cm3) cryst dimens (μm)

Figure 1. Rietveld refinement of the powder X-ray diffraction pattern of Ba2F2Fe1.5Se3 (RBragg = 7.34%; Rp = 10.38%). The black circles represent the experimental intensities. The black line corresponds to the calculated intensities. The difference between the experimental and calculated intensities is displayed as the bottom curve. The Bragg peak positions of Ba2F2Fe1.5Se3 (a), BaF2 (b), and FeSe2 (c) are represented as lines of small dashes. sample thanks to a carbon paste (Electrodag PR406) annealed at 473 K for 2 h under vacuum. The measurements were performed in the 130−410 K range at a bias smaller than 0.01 V.

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RESULTS AND DISCUSSION During the last years, we have undertaken the systematic search of mixed-anion compounds presenting intergrowth structures. This was done by using the concept of layered secondary building units (SBUs).11 Hence, we have synthesized several compounds whose structures result from the alternating stacking of fluorite-type 2D SBUs with other types of 2D SBUs.12,23−25 During this search, we have discovered the sulfide compound Ba2F2Fe1.5S3 built up from the stacking of [Ba2F2]2+ and [Fe1.5S3]2− layers.20 Because of the great interest generated by the discovery of superconductivity in layered iron selenide, we have tried to obtain the selenide analogue of Ba2F2Fe1.5S3. A powder sample of Ba2F2Fe1.5Se3 was therefore synthesized as described in the Experimental Methods. This synthesis yielded an almost pure phase of Ba2F2Fe1.5Se3 with BaF2, BaSe, and Fe3Se4 as the minority impurity phases. A further heating of the reaction product at 1000 °C yielded some crystals. Chemical analysis performed by energy-dispersive X-ray spectroscopy confirmed that the product is a quaternary compound with a composition close to the targeted one (see the Experimental Methods). The structure was subsequently solved using singlecrystal X-ray diffraction. The compound crystallizes in an orthorhombic symmetry with the Pnma space group (all crystallographic information are given in Table 1). Using the structural model of Ba2F2Fe1.5Se3 presented in Table 2, satisfying reliability factors (Robs = 0.0295; Rwobs = 0.0555) were obtained for the 2014 observed reflections with I > 3σ(I) (see the refinement results in Table 1). Using the structural model established on a single crystal of Ba2F2Fe1.5Se3 and taking into account small amounts of BaF2 and FeSe2 impurities, we could successfully refine with the Rietveld method the X-ray diffraction pattern of the synthesized powder (see Figure 1). Figure 2a shows the structure of Ba2F2Fe1.5Se3, which is isostructural with the sulfide Ba2F2Fe1.5S3 compound. In this structure, [Ba2F2]2+ fluorite-type layers alternate regularly with [Fe1.5Se3]2 layers along the b axis. In the [Ba2F2]2+ layer, the F

Powder X-ray diffraction was carried out at room temperature on a Bruker D8 Advance diffractometer (Bragg−Brentano, θ−2θ) equipped with a Lynxeye position-sensitive detector and a copper anticathode. The powder pattern was collected at room temperature from 10 to 90° in 2θ. Analysis of the powder pattern thanks to the PDF database revealed the presence of BaF2 and iron selenide impurities but no evidence of known major phases. The powder pattern was refined with the Jana 2006 chain program starting from the single-crystal structure.21 The comparison shows that the powder and single crystal have similar X-ray diffraction patterns (see Figure 1). Susceptibility measurements were performed with the Quantum Design MPMS XL-7 SQUID magnetometer on a pressed pellet sample (144 mg) in the temperature range 2−480 K. The intrinsic magnetic susceptibility of Ba2F2Fe1.5Se3 was obtained by measuring the slope of the M(H) curve between 25 and 50 kOe and subtracting the ferromagnetic contribution of a small amount of the Fe3Se4 impurity (1.1% by mass) saturating above 10 kOe. This strategy is necessary to extract the correct magnetic susceptibility of Ba2F2Fe1.5Se3 below the Curie temperature (TC = 330 K) of Fe3Se4.22 The susceptibility was corrected from the diamagnetic contributions. The electrical resistivity of Ba2F2Fe1.5Se3 was measured using a fourpoint method on a rectangular sample of 600 μm × 140 μm cut in a pressed pellet. Four golden wire electrodes were pasted onto the B


Article

Inorganic Chemistry Table 2. Crystal Structure of Ba2F2Fe1.5Se3: Atomic Position and Displacement Parameters atom

site

x

y

Ba1 Ba2 Fe1 Fe2 Fe3 Se1 Se2 Se3 Se4 F1 F2 atom

8d 8d 4c 4c 4c 4c 4c 8d 8d 8d 8d

0.24697(4) 0.00344(4) 0.20400(7) 0.04773(7) 0.12459(10) 0.22432(10) 0.02595(10) 0.27200(6) −0.02178(7) 0.1255(3) 0.3746(3) U22

0.57421(3) 0.57438(3) 0.7500 0.7500 0.25 0.7500 0.7500 0.85373(4) 0.64615(5) 0.50119(12) 0.49809(12)

Ba1 Ba2 Fe1 Fe2 Fe3 Se1 Se2 Se3 Se4

U11 0.0110(2) 0.0114(2) 0.0121(4) 0.0126(4) 0.0266(5) 0.0107(5) 0.0111(5) 0.0168(3) 0.0167(3)

0.0120(2) 0.0116(2) 0.0112(5) 0.0126(5) 0.0254(5) 0.0146(6) 0.0134(6) 0.0165(4) 0.0176(4)

Uiso/eq* (Å2)

z

U33

U12

0.0099(11) 0.0103(12) 0.0110(3) 0.0111(4) 0.0324(5) 0.0103(3) 0.0107(3) 0.0136(18) 0.0135(18)

−0.0007(2) 0.0017(2) 0 0 0 0 0 −0.0063(3) −0.0062(3)

0.23278(4) −0.25679(3) −0.1461(13) −0.6400(13) −0.0046(18) 0.23197(9) −0.26200(8) −0.28143(7) −0.77327(7) −0.0113(6) −0.0111(6) U13

0.01101(11) 0.01112(12) 0.0114(2) 0.0121(2) 0.0281(3) 0.0119(3) 0.0117(3) 0.01562(17) 0.01593(17) 0.0154(5) 0.0148(5) U23 −0.0005(9) −0.0011(8) 0 0 0 0 0 0.0027(2) −0.0035(2)

0.00009(9) −0.00042(7) −0.0002(3) 0.0008(3) 0.0170(4) −0.0007(2) 0.00059(20) −0.0011(2) 0.00099(18)

Table 3. Interatomic Distances in the Compound Ba2F2Fe1.5Se3

Figure 2. Crystal structure of Ba2F2Fe1.5Se3 projected along the (110) direction (a), coordination polyhedra of the cations in Ba2F2Fe1.5Se3 (b), and projection of the [Fe1.5Se3] block in the ac plane (c).

atoms are coordinated with four Ba atoms, while the Ba atoms are coordinated with four F and five Se atoms (see Figure 2b). Within the [Fe1.5Se3]2− layers, the Fe atoms occupy three different sites. Fe1 and Fe2 are coordinated with four Se atoms, forming a tetrahedral site. The Fe−Se distances observed in this case range from 2.34 to 2.42 Å (see Figure 2b and Table 3), which is typical of Fe3+ in tetrahedral coordination. For example, in BaFe2Se4 with Fe3+ in the tetrahedral site, the Fe− Se distance is 2.3486(8) Å.26 On the other hand, Fe3 occupies a Se octahedron with larger Fe−Se distances in the range 2.56− 2.78 Å (see Figure 2b and Table 3). These distances are comparable to the average Fe−Se distances found in compounds with Fe2+ in the octahedral sites (2.67 Å in Nd3GaFeSe727 and 2.62 Å in UFeSe328). Figure 2c displays the [Fe1.5Se3]2− layer projected along the b direction. The Fe polyhedra form a peculiar 2D arrangement, where tetrahedra

atom 1−atom 2

distance (Å)

atom 1−atom 2

distance (Å)

Ba1−F2 Ba1−F1 Ba1−F1 Ba1−F2 Ba1−Se3 Ba1−Se3 Ba1−Se1 Ba1−Se4 Ba1−Se4 Ba2−F2 Ba2−F1 Ba2−F1 Ba2−F2 Ba2−Se2 Ba2−Se4 Ba2−Se4 Ba2−Se3 Ba2−Se3

2.655(4) 2.616(4) 2.731(4) 2.695(4) 3.3875(10) 3.5515(10) 3.3915(18) 3.7432(10) 3.3070(10) 2.647(4) 2.622(4) 2.786 (4) 2.661(4) 3.3882(18) 3.5627(10) 3.3724(10) 3.3076(10) 3.7438(10)

Fe1−Se1 Fe1−Se2 Fe1−Se3 Fe1−Se3

2.4075(11) 2.4184(15) 2.3414(13) 2.3414(13)

Fe2−Se1 Fe2−Se2 Fe2−Se4 Fe2−Se4 Fe3−Se1 Fe3−Se2 Fe3−Se3 Fe3−Se3 Fe3−Se4 Fe3−Se4

2.4245(15) 2.4094(11) 2.3461(13) 2.3461(13) 2.5697(16) 2.5774(17) 2.7857(14) 2.7857(14) 2.7807(14) 2.7807(14)

and octahedra alternate along the a axis. Along the c axis, the tetrahedra form 1D chains by corner-sharing. These chains are separated along the a axis by disconnected octahedra linked to the tetrahedra either by edge- or corner-sharing. This particular arrangement of Fe−Se polyhedra is quite unusual among iron selenide compounds. For comparison, Figure 3 presents the different organizations of Fe−Se polyhedra in several ternary or quaternary iron selenide compounds. In most compounds, the Fe atoms adopt a simple tetrahedral coordination and form FeSe4 tetrahedra. These tetrahedra are connected together by edge-sharing to form either isolated pairs like in Ba9Fe4Se16,29 corner-sharing pairs like in Ba2F2Fe2−xSe3,30 infinite chains like in BaFe2Se426 and Ce2O2FeSe2,31 or double chains like in BaFe2Se3.32 A more complex situation is found in Ba4Fe3Se10.26 C


Article

Inorganic Chemistry

Figure 4. Molar susceptibility χ of Ba2F2Fe1.5Se3 measured as a function of the temperature. The cusp at TN = 200 K corresponds to a transition from a paramagnetic to an AFM ordering. The inset displays the χ−1(T) curve and reveals a strong and negative value of the Weiss temperature (θ ≈ −350 K).

law χ(T) = C/(T − θWeiss) gives a Curie constant of 3.1 cm3·K/ mol. This value is close to the one expected for Fe2+ in a highspin (HS; S = 2) state and Fe3+ in an intermediate-spin (IS; S = 3 /2) state, as shown in Table 5. This HS state of Fe2+ in

Figure 3. Different organizations of Fe−Se polyedra in some iron selenide compounds. (a) Isolated pairs of edge-sharing FeSe4 tetrahedra in Ba9Fe4Se16. (b) Infinite chains of edge-sharing FeSe4 tetrahedra in BaFe2Se4. (c) Double chains of edge-sharing tetrahedra in BaFe2Se3. (d) Isolated block of [Fe3Se10] in Ba4Fe3Se10. (e) [Fe3Se10] block made of one octahedron linked to two tetrahedra by edge-sharing in Ba2F2Fe1.5Se3.

Table 5. Calculated Curie Constants (in cm3·K/mol) for the Nine Possible Configurations of Spin States for FeIII+ and FeII+ in Ba2F2Fe1.5Se3

In this compound, the Fe atoms are found in 5- or 6-fold coordination and form Fe3Se10 blocks. The two iron coordination environments found in Ba2F2Fe1.5Se3 are a consequence of the presence of iron with two valence states (FeII+/FeIII+) that can be easily guessed based on oxidation state balance. The presence of FeII+ and FeIII+ was confirmed by preliminary Mössbauer measurements. Despite an important effort, the signal-to-noise ratio was not good enough to quantify accurately the FeII+/FeIII+ ratio. However, the mixed valence was also corroborated by bond valence calculations.33 The calculated oxidation states reported in Table 4 are close to III+ for Fe atoms located in tetrahedra

FeIII+ (tetrahedral site)

FeII+ (octahedral site)

a

Ba1 1.90

Ba2 1.90

Fe1 3.09

Fe2 3.05

IS (S = 3 /2)

LS (S = 1 /2)

HS (S = 2)

5.88

3.38

1.88

IS (S = 1) LS (S = 0)

4.88 4.38

2.38 1.88

0.876 0.375

Ba2F2Fe1.5Se3 (where ⟨dFe−Se⟩ = 2.64 Å within the FeSe6 octahedra) is consistent with the HS state of Fe2+ in FeCr2Se4, where even shorter Fe−Se distances appear (⟨dFe−Se⟩ = 2.55 Å).34 Similarly, an IS state of Fe3+ in Ba2F2Fe1.5Se3 is very likely because the tetrahedral Fe1 and Fe2 sites contain average distances ⟨dFe−Se⟩ of 2.377 and 2.381 Å, respectively (see Table 3). These distances are indeed identical with those of RbFeSe2 (⟨dFe−Se⟩ = 2.384 Å), where the Fe3+ ions are in a tetrahedral environment and display an IS state.35 At low temperature, the existence of an AFM ordering below TN = 200 K is, at first sight, surprising because the different magnetic moments carried by the Fe2+ (S = 2) and Fe3+ (S = 3 /2) ions might rather lead to ferrimagnetism, as in the case of Fe3O4.36 This absence of spontaneous magnetization in Ba2F2Fe1.5Se3 indicates that the magnetic moments of Fe2+ are compensated for and thus arranged antiferromagnetically in the magnetic unit cell below 200 K. Overall, this AFM behavior contrasts drastically with the ferrimagnetic behavior reported for the series of compounds Ba2F2Fe2−xSe3.37 Finally, the electrical resistance of a Ba2F2Fe1.5Se3 crystal was measured with the four-probe method. Figure 5 displays the temperature dependence of the resistivity in the 130−410 K range. At room temperature, the sample resistivity is 565 Ω·cm. This is much higher than the resistivity of metallic FeSe (10−3 Ω·cm)38 but is of the same order of magnitude as the room temperature resistivity observed in La2O2FeSe2 (100 Ω·cm).39 The resistivity of Ba2F2Fe1.5Se3 rises with decreasing temperature, which is typical of an insulating behavior. On the other

Table 4. Bond Valences Estimated from the Brown Method in the Compound Ba2F2Fe1.5Se3a atom valence

HS (S = 5 /2)

Fe3 1.93

Reference: Brown, I. D. J. Appl. Crystallogr. 1996, 29, 479−480.

(Fe1 and Fe2) and close to II+ for Fe atoms located in an octahedral environment (Fe3). Therefore, Ba2F2Fe1.5Se3 is a new example of an iron compound showing an inhomogeneous mixed valence with 1/3 of FeII+ and 2/3 of FeIII+. Figure 4 shows the magnetic susceptibility χ(T) measured on a powder sample of Ba2F2Fe1.5Se3. This sample contained a small amount of BaF2 impurity (≈3%) and Fe3Se4 ferromagnetic impurity (≈1.1%), whose signal was subtracted from the data (see the Experimental Methods for details). Ba2F2Fe1.5Se3 displays a Curie−Weiss susceptibility at high temperature and a cusp at 200 K, followed by a decrease of χ(T) at lower temperature. The χ−1(T) curve, shown in the inset of Figure 4, reveals a strong and negative Weiss temperature (θWeiss ≈ −350 K). This overall behavior is the signature of a paramagnetic system where an AFM ordering occurs below TN = 200 K. The fit of the high-temperature susceptibility by the Curie−Weiss D


Inorganic Chemistry

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ACKNOWLEDGMENTS

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REFERENCES

D.D. thanks the Région Pays de la Loire for providing a financial grant for her Ph.D.

(1) Quebe, P.; Terbüchte, L. J.; Jeitschko, W. J. Alloys Compd. 2000, 302, 70−74. (2) Kamihara, Y.; Watanabe, T.; Hirano, M.; Hosono, H. J. Am. Chem. Soc. 2008, 130, 3296−3297. (3) Zhu, X.; Han, F.; Mu, G.; Cheng, P.; Shen, B.; Zeng, B.; Wen, H.H. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 220512. (4) Zhu, X.; Han, F.; Mu, G.; Zeng, B.; Cheng, P.; Shen, B.; Wen, H.H. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 024516. (5) Palazzi, M. C. R. Acad. Sci. Paris 1981, 292, 789. (6) Otzschi, K.; Ogino, H.; Shimoyama, J.; Kishio, K. J. Low Temp. Phys. 1999, 117, 729−733. (7) Park, Y.; DeGroot, D. C.; Schindler, J. L.; Kannewurf, C. R.; Kanatzidis, M. G. Chem. Mater. 1993, 5, 8−10. (8) Charkin, D. O.; Sadakov, A. V.; Omel’yanovskii, O. E.; Kazakov, S. M. Mater. Res. Bull. 2010, 45, 2012−2016. (9) Cario, L.; Lafond, A.; Morvan, T.; Kabbour, H.; André, G.; Palvadeau, P. Solid State Sci. 2005, 7, 936−944. (10) Cario, L.; Popa, A. F.; Lafond, A.; Guillot-Deudon, C.; Kabbour, H.; Meerschaut, A.; Clarke, S. J.; Adamson, P. Inorg. Chem. 2007, 46, 9584−9590. (11) Cario, L.; Kabbour, H.; Meerschaut, A. Chem. Mater. 2005, 17, 234−236. (12) Kabbour, H.; Cario, L.; Boucher, F. J. Mater. Chem. 2005, 15, 3525−3531. (13) Kabbour, H.; Cario, L.; Jobic, S.; Corraze, B. J. Mater. Chem. 2006, 16, 4165−4169. (14) Wu, G.; Xie, Y. L.; Chen, H.; Zhong, M.; Liu, R. H.; Shi, B. C.; Li, Q. J.; Wang, X. F.; Wu, T.; Yan, Y. J.; Ying, J. J.; Chen, X. H. J. Phys.: Condens. Matter 2009, 21, 142203. (15) Hsu, F.-C.; Luo, J.-Y.; Yeh, K.-W.; Chen, T.-K.; Huang, T.-W.; Wu, P. M.; Lee, Y.-C.; Huang, Y.-L.; Chu, Y.-Y.; Yan, D.-C.; Wu, M.-K. Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 14262−14264. (16) Guo, J.; Jin, S.; Wang, G.; Wang, S.; Zhu, K.; Zhou, T.; He, M.; Chen, X. Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 82, 180520. (17) Ying, T.; Chen, X.; Wang, G.; Jin, S.; Lai, X.; Zhou, T.; Zhang, H.; Shen, S.; Wang, W. J. Am. Chem. Soc. 2013, 135, 2951−2954. (18) Burrard-Lucas, M.; Free, D. G.; Sedlmaier, S. J.; Wright, J. D.; Cassidy, S. J.; Hara, Y.; Corkett, A. J.; Lancaster, T.; Baker, P. J.; Blundell, S. J.; Clarke, S. J. Nat. Mater. 2012, 12, 15−19. (19) Ge, J.-F.; Liu, Z.-L.; Liu, C.; Gao, C.-L.; Qian, D.; Xue, Q.-K.; Liu, Y.; Jia, J.-F. Nat. Mater. 2014, 14, 285−289. (20) Kabbour, H.; Cario, L. Inorg. Chem. 2008, 47, 1648−1652. (21) Petříček, V.; Dušek, M.; Palatinus, L. Z. Kristallogr. - Cryst. Mater. 2014, 229, 345. (22) Terzieff, P.; Komarek, K. L. Monatsh. Chem. 1978, 109, 1037. (23) Kabbour, H.; Janod, E.; Corraze, B.; Danot, M.; Lee, C.; Whangbo, M.-H.; Cario, L. J. Am. Chem. Soc. 2008, 130, 8261−8270. (24) Kabbour, H.; Cario, L.; Danot, M.; Meerschaut, A. Inorg. Chem. 2006, 45 (2), 917−922. (25) Kabbour, H.; Cario, L. Inorg. Chem. 2006, 45, 2713−2717. (26) Berthebaud, D.; Perez, O.; Tobola, J.; Pelloquin, D.; Maignan, A. J. Solid State Chem. 2015, 230, 293−300. (27) Yin, W.; Wang, W.; Kang, L.; Lin, Z.; Feng, K.; Shi, Y.; Hao, W.; Yao, J.; Wu, Y. J. Solid State Chem. 2013, 202, 269. (28) Jin, G. B.; Ringe, E.; Long, G. J.; Grandjean, F.; Sougrati, M. T.; Choi, E. S.; Wells, D. M.; Balasubramanian, M.; Ibers, J. A. Inorg. Chem. 2010, 49, 10455−10467. (29) Berthebaud, D.; Preethi Meher, K. R. S.; Pelloquin, D.; Maignan, A. J. Solid State Chem. 2014, 211, 184−190. (30) Sturza, M.; Allred, J. M.; Malliakas, C. D.; Bugaris, D. E.; Han, F.; Chung, D. Y.; Kanatzidis, M. G. Chem. Mater. 2015, 27, 3280− 3290.

Figure 5. Electric resistivity measured as a function of the temperature for Ba2F2Fe1.5Se3.

hand, no insulator-to-metal transition is observed at high temperature. This indicates that the charge ordering does not melt at high temperature, as observed at the Verwey transition in magnetite Fe3O4.40 In summary, Ba 2 F 2 Fe 1.5 Se 3 is a magnetic insulating compound that does not show any superconductivity. Our results suggest therefore that the mixed-valence Fe2+/Fe3+ seems unfavorable to observe a superconducting behavior in iron selenide compounds. It is worth noting that superconductivity was observed for doped FeSe layers for which the iron valence is intermediate between 1+ and 2+.18 To obtain a mixed-valence Fe+/Fe2+ within the Ba2F2Fe1.5Se3 structure type, we tried to substitute this compound on the Ba site to obtain a Ba2−xLaxF2Fe1.5Se3 (x ≈ 1) compound. However, so far all of our attempts to synthesize this compound and induce superconductivity failed. Substitutions on the Fe site may also be envisioned.41 However, this solution was not investigated in the course of this work because it may lead to a strong disorder on the transition metal layer detrimental to the establishment of a superconducting state.

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CONCLUSION Ba2F2Fe1.5Se3 is a new iron mixed-valence compound. Its structure exhibits intergrowth character with an alternating stacking of [Ba2F2]2+ fluorite-type layers and [Fe1.5Se3]2− layers. This compound contains 1/3 of FeII+ and 2/3 of FeIII+ located in different crystallographic sites. The FeII+ ions are found in octahedral sites, while the Fe III+ ions occupy tetrahedral sites. Magnetic and electrical measurements suggest that Ba2F2Fe1.5Se3 is an AFM insulator with a Néel temperature of around 200 K.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02662. Crystallographic information file of the compound Ba2F2Fe1.5Se3 (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. E


Article

Inorganic Chemistry (31) McCabe, E. E.; Free, D. G.; Evans, J. S. O. Chem. Commun. 2011, 47, 1261−1263. (32) Hong, H. Y.; Steinfink, H. J. Solid State Chem. 1972, 5, 93−104. (33) (a) O’Keefe, M.; Brese, N. E. J. Am. Chem. Soc. 1991, 113, 3226−3229. (b) Brown, I. D. J. Appl. Crystallogr. 1996, 29, 479−480. (34) Ito, M.; Ogawa, T.; Urakawa, S.; Kado, N.; Terada, N. J. Phys.: Conf. Ser. 2012, 400, 032029. (35) Bronger, W.; Kyas, A.; Müller, P. J. Solid State Chem. 1987, 70, 262. (36) Pan, W.; Han, R.; Chi, X.; Liu, Q.; Wang, J. J. Alloys Compd. 2013, 577, 192−144. (37) Sturza, M.; Allred, J. M.; Malliakas, C. D.; Bugaris, D. E.; Han, F.; Chung, D. Y.; Kanatzidis, M. G. Chem. Mater. 2015, 27, 3280. (38) Mizuguchi, Y.; Tomioka, F.; Tsuda, S.; Yamaguchi, T.; Takano, Y. Appl. Phys. Lett. 2008, 93, 152505. (39) McCabe, E. E.; Free, D. G.; Mendis, B. G.; Higgins, J. S.; Evans, J. S. O. Chem. Mater. 2010, 22, 6171. (40) Imada, M.; Fujimori, A.; Tokura, Y. Rev. Mod. Phys. 1998, 70, 1039. (41) Luo, Z.-Z.; Lin, C.-S.; Cheng, W.-D.; Li, Y.-B.; Zhang, H.; Zhang, W.-L.; He, Z.-Z. Dalton Trans. 2013, 42, 9938−9945.

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Ba2F2Fe1.5Se3: An Intergrowth Compound Containing Iron Selenide

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