Angewandte Chemie
DOI: 10.1002/anie.201405453 Chromium Oxyhydride Direct Synthesis of Chromium Perovskite Oxyhydride with a High Magnetic-Transition Temperature** C dric Tassel, Yoshihiro Goto, Yoshinori Kuno, James Hester, Mark Green, Yoji Kobayashi, and Hiroshi Kageyama*
[7] Abstract: We report a novel oxyhydride SrCrO2H directly and cathode material. Their properties arise from the synthesized by a high-pressure high-temperature method. substitution of oxygen with other anions as well as the fine Powder neutron and synchrotron X-ray diffraction revealed tuning of the anionic and interacting d bands of the octahe- that this compound adopts the ideal cubic perovskite structure dral center B. Pm3 m with O2 /H disorder. Surprisingly, despite the non- Unlike the 2p based anions O2 ,F ,S2 ,N3 , the hydride 2 bonding nature between Cr 3d t2g orbitals and the H 1s orbital, H anion is unique and only has a filled 1 s shell. Its it exhibits G-type spin ordering at TN 380 K, which is higher combination with a 2p anion as well as its interactions with the than that of RCrO3 (R = rare earth) and any chromium oxides. B element could be very interesting towards developing novel
The enhanced TN in SrCrO2H with four Cr-O-Cr bonds in magnetic and transport properties. However, preparation of 3+ comparison with RCr O3 with six Cr-O-Cr bonds is reasonably explained by the tolerance factor. The present result offers an effective strategy to tune octahedral tilting in perovskites and to improve physical and chemical properties through mixed anion chemistry.
Oxide perovskites ABO3 are the most encountered compounds in solid-state chemis- try. Their compositional flexibility allows numerous properties often establishing ground- breaking performances in applied devices, such as colossal magneto-resistivity,[1] dielectrics,[2] and high-temperature superconductivity.[3] However, increasing attention has been paid Figure 1. a) Crystal structure of SrCrO2H with cubic perovskite structure ðÞPm3m . Gray strontium, blue chromium, and red/gold anion (oxide/hydride) sites. b) Mass to mixed-anion perovskites, such as oxyfluor- spectrometry of H2 desorption (red) during oxidation of SrCrO2H in flowing oxygen. A ides ABO2F and oxynitrides ABO2N as promis- small peak derived from H2O (green) was also observed. The dotted line plots the [4] ing alternative materials in pigments, water- temperature at the sample, where the rapid increase indicates the exothermic reaction [5] [6] splitting photocatalysis, dielectric properties, upon H2 release/O2 uptake.
oxyhydrides has been a significant challenge, mainly because [*] Dr. C. Tassel, Y. Goto, Y. Kuno, Dr. Y. Kobayashi, Prof. H. Kageyama hydride itself is a strong reducing agent. LaHO and Graduate School of Engineering, Kyoto University Ba21Ge2O5H24 were prepared by solid-state reaction in Kyoto 615-8510 (Japan) [8] E-mail: [email protected] vacuum, while FeAsLa(O,H) superconductors were pre- [9] Dr. C. Tassel pared under high pressure. Topochemical reactions were The Hakubi Center for Advanced Research, Kyoto University employed to yield layered perovskite oxyhydrides LaSr- [10] Kyoto (Japan) CoO3H0.7 and Sr3Co2O4.33H0.84 using CaH2 as a reductant. Dr. J. Hester There has been only one oxyhydride perovskite reported Bragg Institute, Australian Nuclear Science and Technology to date, BaTiO3 xHx that can be prepared through the low- [11] Organization (ANSTO) temperature hydride reduction of BaTiO3. BaTiO3 xHx is Locked Bag 2001, Kirrawee DC NSW 2232 (Australia) non-stoichiometric, with hydride substitutable up to x = 0.6. Prof. M. Green Similar reactions with iron or nickel perovskite oxides did not NIST Center for Neutron Research, National Institute of Standards afford the insertion of hydride, although the products are and Technology highly oxygen deficient (SrFeO , LaNiO ).[12] Herein, we 100 Bureau Drive, MS 6100, Gaithersburg (USA) 2 2 show a stoichiometric oxyhydride perovskite SrCrO H [**] This work was supported by the Hakubi Project funding, MEXT 2 through Grant-in-Aid for Scientific Research A (No. 24248016) and (Figure 1) synthesized using a high-pressure high-temper- the Young Scientist Grant B (No. 25810040) and JSPS through ature technique. This material is the first chromium oxy- 3+ FIRST Program“ and CREST. hydride. We also found that neighboring Cr spins order Supporting information for this article is available on the WWW antiferromagnetically at high temperature (TN 380 K), under http://dx.doi.org/10.1002/anie.201405453. which is rather surprising given the non-bonding nature of
Angew. Chem. Int. Ed. 2014, 53, 10377 –10380 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 10377 Angewandte. Communications
Cr H bonds between Cr 3d t2g and H 1s orbitals. The observed properties are discussed in comparison with the 3+ related RCr O3 family (R = rare earth) that exhibits a spin order at much lower temperatures. In recent years, high-pressure synthesis has been widely used in the synthesis of transition-metal hydrides: binary
systems (e.g., FeH) as well as ternary LiNiH3 and CaPdH3 adopting the perovskite structure.[13] The formation of com- plex metal hydrides usually requires synthesis temperatures that are far beyond the decomposition temperatures of the hydride precursors. While high temperature might favor decomposition of hydrides in the equilibrium of “metal +
H2Ðmetal hydride”, high external and high hydrogen pres- sure will stabilize a solid hydride with a dense structure. The high-pressure and high-temperature reaction tech- nique was therefore chosen as a pathway to yield an oxy-
hydride perovskite SrCrO2H with a dense structure while preventing its decomposition during heating. This composi- tion with Cr in a trivalent state was selected because of its Figure 2. Structural characterization of SrCrO2H by Rietveld refinement stability against reduction; no binary intermediate phase of SPXRD at 290 K (a) and NPD at 300 K (b). The inset in (a) shows an electron diffraction pattern of SrCrO H taken along [001]. Red exists between Cr and Cr O .[14] The best quality was achieved 2 2 3 crosses =observed, green solid line = calculated, and blue solid line = when the stoichiometric mixture of SrH2, SrO, and Cr2O3 was difference intensities. Black dashes =calculated Bragg reflections and heated at 5 GPa and 10008C, yielding a cubic phase with a red dashes =magnetic reflections. A few angle ranges contained tiny 3.83441(2) . Lower pressures and temperatures resulted peaks from an unknown impurity and were excluded from the fit. in low-purity samples containing residual precursors. Higher
temperature reactions led to the reaction of Cr2O3 with the to nuclear peaks, magnetic peaks that are indexed with
NaCl sleeve to give NaCr2O4. Note that attempts to top- a propagation vector (p, p, p; see below). Rietveld analysis on
otactically obtain the target oxyhydride from SrCrO3 were the basis of the O/H disordered model confirmed the
unsuccessful; as previously reported, the CaH2 reaction of presence of hydrogen located at the 3d Wyckoff position
SrCrO3 gave oxygen-deficient phases of SrCrO2.75 and with the refined occupancy of gO = 0.337(2), along with good [15] SrCrO2.8. agreement parameters of Rwp = 3.85% and GOF = 0.96. Note To confirm the presence of hydrogen in our sample, we that the model without hydrogen resulted in an unrealistic 0.7+ monitored, using a mass spectrometer, desorbed gases upon stoichiometry of SrCrO1.338(9) having Cr . No off-stoichiom- heating under oxygen flow (108Cmin 1). Figure 1b shows etry was again found in both cationic sites. It is highly likely
a sharp H2 peak (n = 2) at around 1708C together with that the sample has the stoichiometric composition of
a smaller peak associated with H2O, indicative of a significant SrCrO2H. The refined results are summarized in Table 1. amount of hydrogen in the specimen. After this experiment, We calculated the Goldschmidt tolerance factor of this the sample was studied by X-ray diffraction (XRD), revealing perovskitepffiffiffi oxyhydride, which is defined by t = (rA + rX)/ a mixture of oxidized SrCrO4 and SrCrO3. [ 2(rB + rX)], where rA, rB, and rX denote the ionic radii of the
Synchrotron powder X-ray diffraction (SPXRD) profile A, B, and X site. Using rSr2+ = 132 pm, rCr3+ = 62 pm, and rX = (Figure 2a) was indexed with a primitive cubic structure. The 140 pm as employed in many oxides and pure hydrides,[17] we
obtained lattice parameter of a = 3.83441(2) is slightly obtained t = 1.00 for SrCrO2H, in agreement with the [16] longer than that of SrCrO3 (a = 3.818 ). A few unknown observed cubic structure. The failure to synthesize
peaks not visible in the laboratory XRD were observed. CaCrO2H (not shown) implies that the perfect size matching Rietveld structural analysis was performed using the cubic stabilizes the SrCrO2H phase. We point out that the aliovalent perovskite model Pm3 m , with Sr placed on 1b (0.5, 0.5, 0.5), H for O2 substitution allows the use of larger divalent Sr2+ Cr on 1a (0, 0, 0) and O2 on 3d (0.5, 0, 0). Hydrogen is too light to be observed by XRD and thus is not considered here. The refinement readily converged to reasonable agreement
parameters of Rwp = 8.45% and GOF = 3.85. The oxygen site Table 1: Structural parameters of SrCrO2H from Rietveld refinement of SPXRD (left) and NPD (right) at 300 K.[a] occupancy (gO) of 0.6699(4) indicates a nearly stoichiometric 2 composition of SrCrO2.009(1). No off-stoichiometry was found Atom Site gxyzUiso (100 )
in both cationic sites. Transmission electron microscopy + Sr2 1b 1 0.5 0.5 0.5 1.66(4)/1.95(7) experiments at room temperature demonstrate diffraction Cr3+ 1a 1 0 0 0 0.58(4)/0.86(9) patterns compatible with a simple cubic perovskite (see the O2 3d 0.6699(4)/0.663(2) 0.5 0 0 1.56(9)/1.38(7) inset of Figure 2a). The energy dispersive X-ray spectrometry H 3d -/0.337(2) 0.5 0 0 -/1.38(7) (EDS) confirmed the cation ration of Sr/Cr = 1. [a] Pm3m (no. 221), a = 3.8344(2) . Rwp = 8.45%, Rp =5.44% and Neutron powder diffraction (NPD) profile at room GOF =3.85 for SPXRD at room temperature, and a =3.8333(1) .
temperature (Figure 2b and Figure S1) exhibits, in addition Rwp =3.85%, Rp =2.97% and GOF =0.96 for NPD.
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3+ cations (versus La ). This provides access to reach higher much higher than RCrO3 with six JO bonds? We suppose that t values while preserving the valence of chromium. the enhanced magnetic-ordering temperature arises from the 3+ The room-temperature NPD data revealed magnetic relieved octahedral tilting. It is established that RCr O3 peaks assigned with (p, p, p). A magnetic refinement was structures are always considerably distorted from the ideal performed with G-type spin structure. As shown in Figure 2b, cubic structure because of relatively small trivalent R cations [23] we obtained a good fit with a magnetic moment of 1.90 mB. (rR3+ = 103–121 pm). This leads to smaller t values (below
This observation motivated us to study the temperature 0.95) and as a result, the CrO6 octahedra are tilted relative to evolution of NPD between 25 K and 450 K. The magnetic each other to accommodate the smaller R3+ ions. With moment of 2.37(4) mB was obtained at the base temperature decreasing t (R = La!Lu), the bending of the Cr-O-Cr 3+ 25 K, which is slightly smaller than 3 mB expected for a Cr increases, leading to weakened JO superexchange interaction ion (d3, S = 3/2). Similar values have been indeed reported for and also it enhances the competition between nearest- 3+ Cr -containing perovskite oxides, such as LaCrO3 neighbor (NN) and next-nearest-neighbor (NNN) interac- [18] [19] (2.45 mB) and BiCrO3 (2.55 mB). Conversely, this fact tions. As a consequence, the TN of RCrO3 decreases with 3+ supports the refined composition of SrCr O2H. With decreasing t, as shown in Figure 4. A linear extrapolation of increasing temperature, the magnetic peak decreases gradu- TN toward t = 1 yields TN of 460 K in a non-tilted hypo- ally and finally vanishes at around TN 380 K (Figure 3).
3+ [21] Figure 4. TN values of RCr O3 (R =rare earth) and SrCrO2H plotted as a function of tolerance factor t.
thetical phase of RCrO3. As the Cr-O-Cr angle approaches Figure 3. Temperature dependence of the magnetic moment of the ideal 1808, the orbital overlap integral between Cr 3d t2g SrCrO H determined by Rietveld refinement of NPD. The solid curve is 2 and O 2p orbitals is maximized, which should in turn allow for a guide to the eye. Inset: the normalized (1/2, 1/2, 1/2) magnetic peaks at different temperatures and solid lines represent the Rietveld higher TN. Although two JO bonds are lost per Cr in SrCrO2H, fit. its TN is smaller only by 80 K than the hypothetical cubic RCrO3. In addition, the Cr–O (Cr–H) distance in SrCrO2His
SrCrO2H is a good insulator as in the isoelectric com- 1.917 , which is slightly shorter than the Cr–O distance of 3+ pounds RCr O3, where R is a rare earth, thus allowing approximately 1.98 in RCrO3 (R = La–Lu). This smaller comparative discussions to be made. The observation of TN distance makes JO stronger and contributes to enhance TN.
380 K in SrCrO2H is to our knowledge higher than any It is widely accepted that the physical and chemical chromium oxides (see Table S1 in the Supporting Informa- properties of (layered) perovskite oxides are governed by the tion). For example, Cr2O3 with the corundum structure has tolerance factor. A representative example is manganese [20] 3+ 2+ TN = 307 K. In the case of perovskite oxides RCrO3, the perovskite oxides (R 0.5A 0.5)MnO3, where electronic phases [21] highest TN reported is 290 K in LaCrO3. The significantly including ferromagnetic metal and antiferromagnetic insula- [1] higher TN in SrCrO2H than in RCrO3 is surprising given that tor are tuned by t. Such phase control has been mostly 3+ 3 three d electrons in Cr (d ) are in t2g orbitals that cannot achieved by cation (A and/or B) substitution. The present overlap with H 1s orbitals (i.e., non-bonding). Although study demonstrates that anion substitution is a useful and empty eg orbitals might permit antiferromagnetic spin–spin highly efficient tool to tune t and obtain improved and new interactions by a s-type semi-covalent exchange path, the properties. The H-for-O substitution enables a larger ion, Sr2+ resultant Cr-H-Cr exchange (JH) should be negligibly small. to be used and permits the 1808 angle (while retaining the Thus we suppose that the room-temperature antiferromag- Cr3+ state), so that it is possible to maximize the nearest netism of this material is described mainly by the Cr-O-Cr neighbor JO interactions as well as minimize frustration exchange (JO) that allows antiferromagnetic coupling by p- caused by NN and NNN interactions. superexchange mechanisms between the Cr half-filled t2g Recent structural studies on oxynitride perovskites orbitals and the bridging O 2p orbitals. ABO2N(A = Sr, Ba; B = Ta, Nb) have revealed the cis
A high N el temperature is reported in the layered preference of BO4N2 octahedron, leading to sub-extensive 7.3 [24] oxyhydride LaSrCoO3H0.7 with d (TN = 350 K). This is configurational entropies and unusual “open order”. It is because of the presence of electrons in the Co 3d eg orbital related to the correlated order of displacements in ferro- that provides strong s-type bonds with the H-1s orbital,[10a,22] electric perovskites. Although such a trans effect may be a situation completely different from the present material expected for H , our structure is cubic where O2 /H ions are without eg electrons. What makes the observed TN of apparently disordered. However, if the cis preference is
SrCrO2H with four JO bonds (and negligible two JH bonds) achieved (e.g. by varying reaction conditions), SrCrO2H may
Angew. Chem. Int. Ed. 2014, 53, 10377 –10380 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.angewandte.org 10379 Angewandte. Communications
represent a spin analogue of “open order”. Ultimately, [2] C. Dubourdieu, J. Bruley, T. M. Arruda, A. Posadas, J. Jordan- a dimensional reduction from three to two will occur in cis- Sweet, M. M. Frank, E. Cartier, D. J. Frank, S. V. Kalinin, A. A. constrained ACrOH (A = alkali metal) with disordered Demkov, V. Narayanan, Nat. Nanotechnol. 2013, 8, 748. 2 [3] R. J. Cava, B. Batlogg, J. J. Krajewski, R. Farrow, L. W. Rupp, zigzag Cr-O-Cr chains arranged within the layers (see Fig- A. E. White, K. Short, W. F. Peck, T. Kometani, Nature 1988, 332, ure S2 in the Supporting Information). 814. In conclusion, we have successfully synthesized a novel [4] M. Jansen, H. P. Letschert, Nature 2000, 404, 980. stoichiometric oxyhydride perovskite SrCrO2H through the [5] A. Kasahara, K. Nukumizu, G. Hitoki, T. Takata, J. N. Kondo, M.
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TN value is explained by the relieved octahedral tilting that [8] a) B. Malaman, J. F. Brice, J. Solid State Chem. 1984, 53,44;b)B. enhances the Cr-O-Cr antiferromagnetic coupling and the Huang, J. D. Corbett, Inorg. Chem. 1998, 37, 1892. reduced frustration between nearest neighbor and next- [9] S. Iimura, S. Matsuishi, H. Sato, T. Hanna, Y. Muraba, S. W. Kim, J. E. Kim, M. Takata, H. Hosono, Nat. Commun. 2012, 3, 943. nearest neighbor interactions. In SrCrO2H, the lack of eg [10] a) M. A. Hayward, E. J. Cussen, J. B. Claridge, M. Bieringer, electrons results in a frontier orbital symmetry of H (s) M. J. Rosseinsky, C. J. Kiely, S. J. Blundell, I. M. Marshall, F. L. 2 3 that is different from those of other anions O ,N ,F (s, p). Pratt, Science 2002, 295, 1882; b) R. M. Helps, N. H. Rees, M. A. It would be exciting to prepare, for example, Hayward, Inorg. Chem. 2010, 49, 11062.
Sr1 xLaxCrO2 xHx and SrCrO2 xHx, to continuously modify [11] Y. Kobayashi, O. J. Hernandez, T. Sakaguchi, T. Yajima, T. the tilting angles, carrier concentration, and magnetic inter- Roisnel, Y. Tsujimoto, M. Morita, Y. Noda, Y. Mogami, A. action to develop novel anion-controlled properties. Kitada, M. Ohkura, S. Hosokawa, Z. Li, K. Hayashi, Y. Kusano, J. E. Kim, N. Tsuji, A. Fujiwara, Y. Matsushita, K. Yoshimura, K. Takegoshi, M. Inoue, M. Takano, H. Kageyama, Nat. Mater. 2012, 11, 507. Experimental Section [12] a) Y. Tsujimoto, C. Tassel, N. Hayashi, T. Watanabe, H. A polycrystalline SrCrO2H sample was synthesized by solid-state Kageyama, K. Yoshimura, M. Takano, M. Ceretti, C. Ritter, W. reaction at high pressure and elevated temperature using a cubic anvil Paulus, Nature 2007, 450, 1062; b) M. A. Hayward, M. A. Green, high-pressure apparatus. SrO (99.99%, Aldrich), and Cr2O3 (99.9%, M. J. Rosseinsky, J. Sloan, J. Am. Chem. Soc. 1999, 121, 8843. Kojundo), and laboratory prepared SrH2 were used as starting [13] a) J. V. Badding, R. J. Hemley, H. K. Mao, Science 1991, 253, 421; reagents. The appropriate amounts of starting reagents were mixed b) S. Ayukawa, K. Ikeda, M. Kato, T. Noji, S. Orimo, Y. Koike, J. thoroughly in an agate mortar in the glovebox. The mixed sample was Phys. Soc. Jpn. 2012, 81, 034704; c) R. Sato, H. Saitoh, N. Endo, charged into a NaCl sleeve as a pressure-transmitting medium inside S. Takagi, M. Matsuo, K. Aoki, S. Orimo, Appl. Phys. Lett. 2013, a graphite heater. The pressure applied ranges 4–8 GPa and the 102, 091901. sample was heated at 700–11008C. After heating to the target [14] V. Peres, L. Favergeon, M. Andrieu, J. C. Palussi re, J. Balland, temperature in 10 min, the temperature was stabilized for 30 min and C. Delafoy, M. Pijolat, J. Nucl. Mater. 2012, 423, 93. quenched to room temperature within 3 min followed by the slow [15] A. M. Ar valo-L pez, J. A. Rodgers, M. S. Senn, F. Sher, J. release of the pressure. The presence of hydrogen in the product was Farnham, W. Gibbs, J. P. Attfield, Angew. Chem. 2012, 124, investigated using a Bruker MS9610 quadrupole mass spectrometer. 10949; Angew. Chem. Int. Ed. 2012, 51, 10791. 1 The sample was heated at 5 Kmin under O2 flow and gaseous [16] B. L. Chamberland, Solid State Commun. 1967, 5, 663. products were monitored simultaneously. TEM data was collected at [17] K. Ikeda, Y. Nakamori, S. Orimo, Acta Mater. 2005, 53, 3453. room temperature with a JEM 1400 microscope (JEOL). SPXRD [18] E. F. Bertaut, G. Bassi, G. Buisson, P. Burlet, J. Chappert, A. experiments were performed on a Debye–Scherrer camera at the Delapalme, J. Mareschal, G. Roult, R. Aleonard, R. Pauthenet, BL02B2 beamline at SPring-8. The NPD data for refinement were J. P. Rebouillat, J. Appl. Phys. 1966, 37, 1038. collected between 25 K and 385 K using a Cu311 monochromator [19] A. A. Belik, S. Iikubo, K. Kodama, N. Igawa, S. Shamoto, E. (l = 1.5401 ) at NIST Center for Neutron Research. The temper- Takayama-Muromachi, Chem. Mater. 2008, 20, 3765. ature evolution was also studied at the WOMBAT diffractometer of [20] a) T. R. McGuire, E. J. Scott, F. H. Grannis, Phys. Rev. Lett. 1956, the Bragg Institute at ANSTO. Structural refinements were carried 102, 1000; b) A. Iyama, T. Kimura, Phys. Rev. B 2013, 87, out using JANA2006.[25] EDS was collected by an Oxford x-act 180408(R). detector mounted on a Hitachi S-3400N SEM. [21] a) R. Aleonard, R. Pauthenet, J. P. Rebouillat, C. Veyret, J. Appl. Phys. 1968, 39, 379; b) I. Weinberg, P. Larssen, Nature Received: May 20, 2014 1961, 192, 445. Published online: August 12, 2014 [22] S. J. Blundell, I. M. Marshall, F. L. Pratt, M. A. Hayward, E. J. Cussen, J. B. Claridge, M. Bieringer, C. J. Kiely, M. J. Rosseinsky, Keywords: chromium · high-pressure chemistry · Physica B 2003, 326, 527. . [23] a) R. D. Shannon, Acta Crystallogr. Sect. A 1976, 32, 751; mixed anion phases · oxyhydrides · perovskites b) R. D. Shannon, C. T. Prewitt, Acta Crystallogr. Sect. B 1969, 25, 925. [24] M. Yang, J. Or -Sol , J. A. Rodgers, A. Bel n Jorge, A. Fuertes, J. P. Attfield, Nat. Chem. 2011, 3, 47. [25] V. Petricek, M. Dusek, L. Palatinus, Z. Kristallogr. 2014, 229(5), [1] C. N. R. Rao, B. Raveau, Colossal Magnetoresistance, Charge 345. Ordering and Related Properties of Manganese Oxides, World Scientific, Singapore, 1998.
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