Pressure-Stabilized Cubic Perovskite Oxyhydride BaScO2H

Apr 11, 2017 - Alternatively, high-pressure reactions have been recently employed to synthesize perovskite-based TM oxyhydrides of SrCrO2H,(9) Sr2V(O,...
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Pressure-Stabilized Cubic Perovskite Oxyhydride BaScO2H Yoshihiro Goto,† Cédric Tassel,† Yasuto Noda,‡ Olivier Hernandez,§ Chris J. Pickard,∥,⊥ Mark A. Green,# Hikari Sakaebe,∇ Noboru Taguchi,∇ Yoshiharu Uchimoto,○ Yoji Kobayashi,† and Hiroshi Kageyama*,† †

Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan § Institut des Sciences Chimiques de Rennes, UMR CNRS 6226, Université de Rennes 1, Bâtiment 10B, Campus de Beaulieu, Rennes F-35042, France ∥ Department of Materials Science & Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom ⊥ Advanced Institute for Materials Research (AIMR), Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan # School of Physical Sciences, University of Kent, Canterbury CT2 7NR, United Kingdom ∇ National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577, Japan ○ Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan ‡

S Supporting Information *

ABSTRACT: We report a scandium oxyhydride BaScO2H prepared by solid state reaction under high pressure. Rietveld refinements against powder synchrotron X-ray and neutron diffraction data revealed that BaScO2H adopts the ideal cubic perovskite structure (Pm3̅m), where oxide (O2−) and hydride (H−) anions are disordered. 1H nuclear magnetic resonance (NMR) spectroscopy provides a positive chemical shift of about +4.4 ppm, which can be understood by the distance to the nearest (and possibly the next nearest) cation from the H nucleus. A further analysis of the NMR data and calculations based on ab initio random structure searches suggest a partial cis preference in ScO4H2 octahedra. The present oxyhydride, if compositionally or structurally tuned, may become a candidate for H− conductors.

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Sr, Ba, and Eu),8,13 possibly related to hydride’s adjustability to fit its size with oxide anion, ensure potential applications for a wide range of electronic devices. Finally, the labile nature of hydride in BaTi(O,H)3 provides new multistep topochemical routes to access mixed anion compounds such as BaTi(O,N)3 with ferroelectricity14 and BaTi(O,H,OH)3 with unprecedented coexistence of H− and H+.15 Unlike p- and f-block oxyhydrides, synthesis of TM oxyhydrides is not straightforward. This is partly because the synthesis requires highly reducing conditions, but this must be done without transferring an electron from the hydride to the TM cation. To circumvent this difficulty, a low-temperature topochemical reaction using CaH2 as a reductant as well as a hydrogen source has been employed to synthesize LaSrCoO3H0.7,4 ATi(O,H)3,6−8 and Srn+1VnO2n+1Hn (n = 1, 2, ∞)10 from the corresponding oxide precursors. Alternatively, highpressure reactions have been recently employed to synthesize perovskite-based TM oxyhydrides of SrCrO2H,9 Sr2V(O,H)4,11 and LaSrMnO3.3H0.7,12 using binary oxides and hydrides as starting reagents. The latter method is advantageous for obtaining perovskite-based compounds based on the cubic close packed structure. Additionally, application of high

INTRODUCTION The presence of hydride anions in transition-metal (TM) oxides has long been an issue of debate in solid state ionics. On the basis of electrochemical characterization, it was speculated that the charge transport involving hydrogen-containing ions in SrTiO3-based oxides appears to gain a contribution from a negatively charged species under reducing conditions.1−3 In 2002, LaSrCoO3H0.7 with an n = 1 Ruddlesden−Popper (RP) layered perovskite structure was reported as a first explicit example of TM perovskite oxyhydride,4 which was followed by a report on the n = 2 analogue.5 Subsequent exploratory research has led to the discovery of a series of perovskite-based TM oxyhydrides containing titanium,6−8 chromium,9 vanadium,10,11 and manganese.12 These relatively new types of solids exhibit novel magnetic, transport, and chemical properties. First, fairly strong σ bonding in LaSrCoO3H0.7 between Co 3dx2−y2 and H 1s orbitals not only stabilizes this material but also provides strong superexchange integrals, making a magnetic transition far beyond room temperature. 4 A cation/anion cosubstituted perovskite SrCr3+O2H with respect to the isoelectronic RCr3+O3 (R = rare earths) offers a new pathway to extensively tune tolerance factor t, leading to a higher Néel temperature for SrCrO2H (t ∼ 1) than for any Cr(III) oxides.9 Second, excellent electric conductivity as well as thermal stability in ATi(O,H)3 (A = Ca, © 2017 American Chemical Society

Received: November 27, 2016 Published: April 11, 2017 4840

DOI: 10.1021/acs.inorgchem.6b02834 Inorg. Chem. 2017, 56, 4840−4845

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Inorganic Chemistry

= multiplicity), yio and yic are the observed and calculated intensities, Fho and Fhc are the observed and calculated structure factors, wi is the weighting factor, N is the total number of yio data when the background is refined, and P is the number of refined parameters. Thermogravimetric and differential thermal analysis (TG-DTA) was conducted with a TG-DTA 2000S (Bruker AXS) under flowing O2 at 300 mL/min. A platinum pan was used as a sample holder and aluminum oxide as a reference. The sample (17.5 mg) was heated at 10 °C/min up to 1000 °C. A hydrogen release behavior upon heating was monitored by a quadrupole mass spectrometer (QMS, MS9610, Bruker AXS) connected to the TG-DTA Instruments. Annular dark field scanning transmission electron microscope (ADF-STEM) image and selected area electron diffraction (SAED) patterns of the product were recorded using a TITAN3 G2 60-300 (FEI) transmission electron microscope with a vacuum transfer holder (GATAN 648). The samples were transferred to the electron microscope from the glovebox without exposure to the ambient atmosphere using the transfer holder. We obtained 1H magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectra using a home-built spectrometer at an operating frequency of 301.38 MHz. For background reduction, a Chemagnetics 5 mm CRAMPS probe was employed with a background suppression pulse sequence. The nutation frequency and the MAS rate were 74 and 8.5 kHz, respectively, and the pulse delay was 5 s. Chemical shifts were externally referenced to trimethylsilane. Ab initio random structure searches (AIRSS)21 were performed to predict a stable structure. First-principles calculations were undertaken using the plane wave CASTEP22 DFT code and the Perdew−Burke− Ernzerhof (PBE) exchange-correlation functional. Vanderbilt ultrasoft pseudopotentials,23 a plane-wave basis-set energy cutoff of 340 eV, and k-point spacing of 2π × 0.7 Å were used for the prediction. The candidate structures were then further refined using default CASTEP version 7.0 pseudopotentials, a plane-wave basis-set energy cutoff of 1000 eV, and k-point spacing of 2π × 0.05 Å.

pressure would favor production of solids, rather than competing reactions giving rise to gaseous products. It has recently been demonstrated that a layered perovskite (La,Sr)2Li(O,H)4 with Li+ at the octahedral (B) site is a pure hydride conductor.16 Exploratory synthesis of electronically insulating oxyhydrides for developing high-energy-density storage and conversion devices is thus an important subject. Herein, we report synthesis of a scandium oxyhydride perovskite BaScO2H. Unlike ambient-pressure reactions that yield an oxygen-deficient oxide17,18 or oxide-hydroxide,19 a high-pressure condition beyond a few GPa stabilizes a new phase with incorporation of hydride anion in the oxide lattice. Powder synchrotron X-ray diffraction (SXRD), powder neutron diffraction (ND), and transmission electron microscopy (TEM) experiments revealed that BaScO2H adopts the ideal cubic perovskite structure without any anion (O/H) order, though implications of cis-preference of ScO4H2 octahedron are suggested from theoretical calculations. A positive chemical shift in 1H NMR is discussed in connection with a recently proposed empirical relation.

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EXPERIMENTAL SECTION

A polycrystalline sample of BaScO2H was synthesized by solid state reaction under high pressure, using BaO (99.99%, Aldrich), Sc2O3 (99.9%, Kojundo), and BaH2 as starting reagents. BaH2 was prepared by heating elemental Ba (99%, Kojundo) under H2 flow (99.99%, Sumitomo Seika) at 575 °C. A stoichiometric mixture of these reagents was ground thoroughly in a N2-filled glovebox (H2O, O2 < 0.1 ppm) and sealed in a NaCl capsule inside a pyrophyllite cell with a graphite heater. The cell was compressed to a pressure of 7 GPa using a cubic anvil press, heated at 1000 °C for 30 min, and quenched to room temperature within 3 min followed by a slow release of the pressure. BaH2 and BaScO2H were highly air-sensitive so they must be handled in an inert atmosphere. For comparison, we attempted hydride reactions on Ba2Sc2O5 to yield anion-exchanged BaScO2H. A mixture of Ba2Sc2O5 and 2 molar excess CaH2 (99.99%, Aldrich) in a sealed, evacuated Pyrex tube was reacted at 350−550 °C for 66 h. Powder X-ray diffraction (XRD) measurements of the obtained products were carried out using a D8 ADVANCE diffractometer (Bruker AXS) with Cu Kα radiation. Since the sample was highly airsensitive, it was covered with polyimide (Kapton) tape in the N2-filled glovebox. High-resolution synchrotron XRD (SXRD) measurements were performed using a large Debye−Scherrer camera with an imaging plate as a detector installed at BL02B2 in SPring-8, JASRI. The incident X-ray from a bending magnet was monochromatized to a wavelength of λ = 0.42067 Å by the 111 reflection of a Si crystal. A finely ground powder sample was sieved through a 32 μm mesh, put into a Pyrex capillary (0.2 mm i.d.), and sealed in the glovebox. The sealed capillary was rotated during measurements in order to reduce preferential orientation of crystallites. A powder ND measurement was conducted at 10 K using a highresolution powder diffractometer BT-1 with 32 3He neutron detectors installed at the National Institute of Standards and Technology (NIST) Center for Neutron Research. Incident neutrons were monochromatized to λ = 1.5403 Å by the 311 reflection of a Cu crystal. The sample of about 1 g was placed into a vanadium cylinder and sealed by an indium wire in a He-filled glovebox. We used a deuterated sample so as to reduce incoherent scattering and signal-tonoise ratio. BaD2 was prepared by heating elemental Ba under D2 flow (99.99%, Sumitomo Seika) at 575 °C. The collected SXRD and ND patterns were analyzed by the Rietveld method using the FULLPROF program.20 A Thompson− Cox−Hastings pseudo-Voigt profile function was applied to fit the patterns. Agreement factors were the following: the R-weighted profile factor, Rwp = [∑wi(yio − yic)2/∑wi(yio)2]1/2; R-profile, Rp = ∑|yio − yic|/∑(yio); goodness of fit (GOF), χ2 = [Rwp/Rexp]2, where Rexp = [(N − P)/∑wiyio2]1/2 and RBragg = ∑|Iho − Ihc|/∑(Iho), where Ih = mFh2 (m

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RESULTS AND DISCUSSION

The laboratory XRD pattern of the sample synthesized at 7 GPa and 1000 °C (Figure S1 in the Supporting Information) was readily indexed using a primitive cubic structure with a = 4.1518(5) Å. No peaks associated with impurities or superstructures were found. The XRD pattern differs clearly from that of oxygen-deficient Ba2Sc2O5 with a tetragonal unit cell of a = 4.1517 Å and c = 3.9857 Å (Z = 1)17 or a = 4.15 Å and c = 24.05 Å (Z = 6),18 whereas it resembles that of BaScO2(OH) adopting the ideal perovskite structure (a = 4.17 Å).19 As shown in Figure S2, unidentified peaks were detected with reaction at pressure less than 7 GPa. The cubic phase degreased with decreasing pressure and disappeared at 2 GPa. These observations indicate that the cubic structure is a pressurestabilized phase. Figure 1a represents the SXRD pattern at room temperature. Together with the main cubic phase (a = 4.15035(3) Å), we found additional reflections with their intensities being less than 5% of the main phase. Most of them were assigned to NaCl from the capsule and to an unknown cubic phase with a = 4.1942(2) Å (Figure S3a). Rietveld refinement was performed assuming for the main phase the ideal perovskite BaScO3−x with structural model (space group of Pm3̅m), with Ba, Sc, and O atoms placed at the Wyckoff positions of 1b (1/2, 1/2, 1/2), 1a (0, 0, 0), and 3d (1/2, 0, 0), respectively. NaCl was added as a secondary phase. The 111 and 200 reflections of the main phase were excluded from the refinement due to overlap with unidentified peaks. The isotropic thermal parameters Biso’s of all the atoms and the occupation factor of oxygen g(O) were allowed to vary. 4841

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Figure 2. Mass spectrometry of H2 (mass no. 2) desorption with DTA curve and mass increase during the heating of BaScO2H in flowing oxygen.

and a drastic mass increase. This implies a conversion to a thermodynamically stable phase Ba2Sc2O5 at ambient pressure, which was verified by XRD. We note that the mass increase of 2.90% gives the initial composition of BaScO2.10(Hx) when one assumes the final composition of BaScO2.5. The slight deviation of the oxygen content is acceptable given the presence of impurities and/or a partial reaction of the air-sensitive BaScO2H sample prior to the TG/DTA measurements. The difference in neutron scattering lengths of oxygen and deuterium (O = 5.803 fm and D = 6.671 fm)24 enables one to determine the anionic composition by ND. In Figure 1b and Figure S3b, we show the ND pattern collected at 10 K. In addition to the main cubic phase with a = 4.14386(4) Å, we found additional reflections ascribed mostly to NaCl, which was added as a secondary phase for the Rietveld refinement. 110, 211, and 321 reflections of the main phase were excluded due to overlap with unidentified peaks. The initial refinement based on an oxygen-deficient phase BaScO3−x yielded the oxygen content of 3.16(4) (x = −0.16), which is inconsistent with the synchrotron refinement and the charge-neutrality condition. Accordingly, we tested a BaScO3−xDy composition, where O and D atoms were randomly distributed with the following constraints: Bij(O) = Bij(D) and g(D) = 5−2 × g(O). This resulted in the reasonable composition of BaScO2.000(9)D1.001(17). The refined parameters are given in Table 1, and the crystal structure is shown in Figure 3. We calculated the Goldschmidt tolerance factor for BaScO2H, which is defined by t = (rBa + rO/H)/[√2(rSc + rO/H)]), where rBa, rSc, and rO/H denote the ionic radii for Ba, Sc, and O/

Figure 1. Structural characterizations of BaScO2H(D) by Rietveld refinement of (a) SXRD at room temperature and (b) ND at 10 K. Red crosses and green and blue solid lines represent observed, calculated, and difference intensities, respectively. The first and the second rows of black ticks indicate the position of the Bragg reflections of BaScO2H and NaCl. The volume fraction of NaCl was 4.7 wt % (SXRD) and 9.1 wt % (ND) when other impurity contributions were omitted.

The refinement converged smoothly to reliable factors of Rwp = 11.4% and GOF = 2.25. The refined parameters are given in Table 1. Reasonably small values of Biso were obtained for all Table 1. Structural Parameters of BaScO2H(D) Obtained from Rietveld Refinement of SXRD at Room Temperature (Left) and ND at 10 K (Right)a atom

site

Ba Sc

1b 1a

O

3d

−/D

3d

x

y

z

Biso or Beq (Å2)

1 1

1/2 0

1/2 0

1/2 0

0.660(9)/ 0.667(3) −/0.334(6)

1/2

0

0

0.560(4)/0.122 0.768(15) /0.485 0.76(7)/1.457

1/2

0

0

−/1.457

g

a

Space group Pm3̅m, a = 4.15034(3) Å, Rwp = 11.4%, Rp = 8.9%, GOF = 2.25, RBragg = 2.01% for SXRD, and a = 4.14386(4) Å, Rwp = 15.8%, Rp = 20.0%, GOF = 1.61, RBragg = 3.65% for ND.

the atoms. Varying occupation factors of Ba and Sc did not improve the refinement. Most importantly, g(O) was refined to 0.660(9), which is much smaller than g(O) = 1 for BaScO2(OH). Given the formal charge of Ba2+, Sc3+, and O2−, the estimated composition of BaScO1.98(3) is unrealistic and suggests a plausible formation of BaScO2H. For the assessment of hydrogen in the sample, QMS measurement was conducted upon heating under O 2 atmosphere. As expected, we observed a significant amount of H2 at ∼200 °C as shown in Figure 2. This hydrogen release is accompanied by a large exothermic peak in the DTA curve

Figure 3. Crystal structure of BaScO2H with cubic perovskite structure (Pm3̅m). Green, orange, red, and blue spheres represent Ba, Sc, O, and H, respectively. 4842

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structures with space groups P3221, C2221, C2/c, and P4/mmm (Figure S6 and Table S1). These structures with cis configurations are found always to be more stable than the infinite layer structure with the trans configuration. Among the tested structures, the most stable structure is the one with a √2 × √2 × 2 supercell (space group P3221). In order to experimentally observe a possible superstructure arising from the anion order, we performed high-resolution transmission electron microscopy experiments for BaScO2H. However, as shown in Figure 4 and Figure S7, ADF images and SAED

H. We used the Shannon ionic radii of rBa = 1.61 Å, rSc = 0.745 Å, and rO/H = 1.40 Å (with the coordination numbers of 12, 6, and 6, respectively)25,26 and obtained t = 0.992, which is very close to unity. This supports the observed cubic symmetry without any octahedral rotations. The oxidation state of each site was calculated using the bond valence sums (BVS) method.27,28 When the statistical average contribution of O2− and H− (2:1) to cations was assumed, the BVS values for Ba and Sc yielded, respectively, +1.99 and +2.88, which agree well with the formal charges of Ba2+ and Sc3+. On the contrary, the BVS calculations for anions gave −1.79 for O and −1.28 for H, indicating that O and H are slightly underbonded and overbonded. This is not surprising given the disordered arrangement of aliovalent anions. The present result demonstrates, together with the recent reports,9,11,12 that the high-pressure technique is a fairly useful approach for preparing perovskite-based TM oxyhydrides. While Sr2VO3H can be prepared both by high-pressure reaction and topochemical hydride reaction,10,11 SrCrO2H and LaSrMnO3H0.7 are only accessible by high-pressure reaction;9,12 the hydride reactions of SrCrO3 and LaSrMnO4 with CaH2 result in oxygen-deficient phases of SrCrO2.75 and LaSrMnO4−x (x = 0.33, 0.5).29,30 As mentioned earlier, only the oxygen-deficient perovskite-type structure Ba2Sc2O5 in tetragonal symmetry is reported as an ambient-pressure phase, although precise structural information is unavailable.17,18 Several hydride reactions for Ba2Sc2O5 were tested to check a possible anion exchange to yield BaScO2H. While we found no reaction after hydride reactions at 350 and 450 °C for 66 h, a reaction at 550 °C resulted in a cubic phase with a = 4.16−4.25 Å (see Figure S4), which is longer than a = 4.15034(3) Å in BaScO2H. This result may suggest a partial 2H-for-O exchange, leading to BaScO2+xH2x (0 < x < 0.5). However, rather broad diffraction peaks and the lack of structural information on Ba2Sc2O5 do not allow us to conclude regarding the formation of a solid solution. It is noteworthy that octahedral tilting has not been reported in anion-disordered perovskite oxyhydrides in ABO 2H stoichiometry. SrCrO2H with t = 0.997 also adopts the cubic perovskite.9 From the failed synthesis of SrScO2H (t = 0.936) and CaCrO2H (t = 0.962) (Figure S5), one may claim that oxyhydride perovskites are less tolerable to octahedral rotation. A similar tendency can be seen for other mixed anion perovskite ABO2X compounds, with the greatest distortion found in SmZrO2N (t = 0.878) for oxynitrides and in NaNbO2F (t = 0.951) for oxyfluorides,31,32 both with an a+b−b− tilting in Glazer notation.33 These t values are much larger than t ∼ 0.8 for ABO3 oxides.34 Anion order/disorder is one of the important issues in mixed anion compounds. Yang and co-workers recently discovered a novel anion-ordered state in d0 perovskite oxynitrides SrMO2N (M = Nb5+, Ta5+), derived from the preference in cis-MO4N2 configuration over trans.35 It is argued that the cis preference of MO4N2 octahedra arises from the stronger covalency of nitride anion due to lower electronegativity, affording a strong N(pπ)− M(dπ)−N(pπ) interaction in this configuration.36,37 Likewise, the MO2N4 octahedra in AMON2 favor the cis configuration, as also verified in some complexes with two weakly bonded ligands.38,39 Since the hydride ion in BaScO2H consists only of a 1s orbital orthogonal with Sc t2g orbitals, the cis configuration with more O(pπ)−Sc(dπ)−O(pπ) bonds may be favorable. We conducted ab initio random free searches to examine the cis/trans preference. The calculations identified four stable

Figure 4. (a) STEM-ADF picture and (b) SAED pattern of BaScO2H projected along [001].

patterns only supported the cubic perovskite structure, and no superstructure reflections were obtained, indicating that oxide and hydride anions are disordered. The absence of anion order is possibly explained in terms of an entropy effect as this material was synthesized at 1000 °C followed by rapid quenching. A low-temperature annealing under pressure may eventually induce an anion order in this system. In order to investigate the local environment of hydrogen in BaScO2H, a 1H MAS NMR measurement was conducted at room temperature. As shown in the inset of Figure 5a, the

Figure 5. (a) 1H MAS NMR spectrum (black) showing a resonance centered at 4.4 ppm. Blue and green lines correspond to hydride anions with and without neighboring hydride anion(s), respectively. The red line is the total fit. A small peak at 0.84 ppm (brown) comes from a rotor cap. Inset shows the whole spectrum with spinning side bands. (b) Calculated ratio of trans−trans configuration for an N × N × N cell. 4843

DOI: 10.1021/acs.inorgchem.6b02834 Inorg. Chem. 2017, 56, 4840−4845

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local preference for cis-ScO4H2 octahedra. Although our attempts to probe H− conductivity in BaScO2H have so far been unsuccessful, introduction of anion-site vacancy in BaScO2H by preparing a solid solution between BaScO2H and Ba2Sc2O5 could possibly promote hydride diffusion. This would be interesting as it should give a three-dimensional H− diffusion pathway, as opposed to the two-dimensional one proposed in (La,Sr)2Li(O,H)4.

spectrum has a symmetric peak centered at around 4 ppm with spinning side bands. A closer look at the spectrum shows that the central peak consists of sharp and broad components (Figure 5a). Note that a small peak at 0.84 ppm originates from the rotor cap due to an incomplete background suppression pulse sequence. Fits of the central spectrum to the Lorentzian function give almost the same chemical shifts of 4.398(4) ppm for the sharp peak (fwhm = 0.44(1) ppm) and 4.41(2) ppm for the broad one (fwhm = 8.71(9) ppm). This indicates that hydrogen is being occupied at the unique site (or in a very similar environment), in agreement with the Rietveld structural analysis. The presence of broad peak with spinning side bands is interpreted in terms of dipole interaction with neighboring hydride(s). Namely, the sharp peak can be assigned as a hydride anion without any nearest neighbor hydride anions, while the broad peak with spinning side bands is assigned as the one with nearest neighbor hydride anion(s). The total spectrum was fitted to the exponentially modified Lorentzian function, from which the ratio of the sharp peak to the broad peak with spinning side bands was determined to be 2.7(2)% (Figure 5). The local hydride arrangement in the anionic lattice was examined computationally with an N × N × N cell, where we assumed complete anion disorder while we imposed a constraint that each Sc center is coordinated by 4 oxide anions and 2 hydride anions. This constraint gives rise to three types of hydrogen configurations, where the bridging hydride anion in neighboring octahedra forms cis−cis, cis−trans, and trans−trans configurations (Figure S8). For each cell (N), we counted the number of these configurations, and this procedure was repeated over 1000 times to get averaged estimates as shown in Figure 5b and Figure S9. The calculated ratio of the trans− trans configuration is 5.3% for N = 120, which is larger than the experimentally observed value (2.7%). This may suggest a partial cis preference, but given the possible errors in the fitting, further studies are necessary to confirm this. Finally, let us discuss the chemical shift of the 1H MAS NMR spectrum. Hayashi and co-workers demonstrated, for non-TM and nonperovskite (oxy)hydrides, an empirical relationship between the chemical shift of hydride anion and the distance from the hydride to the nearest neighbor cation dM−H,40 which is given by δ(H−) (ppm) = 0.070dM − H (pm) − 11.5

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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.6b02834. Figures showing XRD data, computed crystal structures, ADF STEM image, local structural information, and table with lattice parameters and atomic coordinates (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Hiroshi Kageyama: 0000-0002-3911-9864 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Grant-in-Aid for Encouragement of Young Scientists B (No. 25810040) from JSPS. NMR and TEM studies were supported by JSPS Grant-in-Aid for Scientific Research on Innovative Areas “Mixed Anion” (JP16H06439, JP16H06440, and JP16H06441) from MEXT and CREST (JPMJCR1421). C.J.P. acknowledges support from the Engineering and Physical Sciences Research Council (EPSRC) [EP/G007489/2], and the Royal Society through a Wolfson Research Merit Award.

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REFERENCES

(1) Steinsvik, S.; Larring, Y.; Norby, T. Hydrogen Ion Conduction in Iron-Substituted Strontium Titanate, SrTi1−xFexO3−x/2 (0 ≤ x ≤ 0.8). Solid State Ionics 2001, 143, 103−116. (2) Widerøe, M.; Münch, W.; Larring, Y.; Norby, T. Proton and Apparent Hydride Ion Conduction in Al-Substituted SrTiO3. Solid State Ionics 2002, 154, 669−677. (3) Norby, T.; Widerøe, M.; Glöckner, R.; Larring, Y. Hydrogen in Oxides. Dalton Trans. 2004, 3012−3018. (4) Hayward, M. A.; Cussen, E. J.; Claridge, J. B.; Bieringer, M.; Rosseinsky, M. J.; Kiely, C. J.; Blundell, S. J.; Marshall, I. M.; Pratt, F. L. The Hydride Anion in an Extended Transition Metal Oxide Array: LaSrCoO3H0.7. Science 2002, 295, 1882−1884. (5) Helps, R. M.; Rees, N. H.; Hayward, M. A. Sr3Co2O4.33H0.84: An Extended Transition Metal Oxide-Hydride. Inorg. Chem. 2010, 49, 11062−11068. (6) Kobayashi, Y.; Hernandez, O. J.; Sakaguchi, T.; Yajima, T.; Roisnel, T.; Tsujimoto, Y.; Morita, M.; Noda, Y.; Mogami, Y.; Kitada, A.; Ohkura, M.; Hosokawa, S.; Li, Z.; Hayashi, K.; Kusano, Y.; Kim, J. e.; Tsuji, N.; Fujiwara, A.; Matsushita, Y.; Yoshimura, K.; Takegoshi, K.; Inoue, M.; Takano, M.; Kageyama, H. An Oxyhydride of BaTiO3 Exhibiting Hydride Exchange and Electronic Conductivity. Nat. Mater. 2012, 11, 507−511. (7) Sakaguchi, T.; Kobayashi, Y.; Yajima, T.; Ohkura, M.; Tassel, C.; Takeiri, F.; Mitsuoka, S.; Ohkubo, H.; Yamamoto, T.; Kim, J. E.; Tsuji, N.; Fujihara, A.; Matsushita, Y.; Hester, J.; Avdeev, M.; Ohoyama, K.;

(1)

The linear increase of the chemical shift means that electron density (derived from H− 1s2 shell) around the hydrogen nucleus decreases in proportion to dM−H. Using dSc−H = 2.075 Å, the chemical shift for BaScO2H is calculated as δ(1H) = 3.1 (±2) ppm, which is smaller than the experimental value of 4.398(4) and 4.41(2) ppm, but could be acceptable given the error of the formula (±2). Alternatively, the deviation may indicate a necessity to include the second-nearest neighbor cation Ba2+ with dBa−H = 2.935 Å. Owing to the size and shape flexibility of hydride and the electropositivity of barium,41 Ba2+ could also contribute, to a certain extent, to reduce the electron density near the hydrogen nucleus.

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SUMMARY A high-temperature and high-pressure reaction has produced BaScO2H, a new addition to the TM perovskite oxyhydride family. Experimental studies show that BaScO2H crystallizes in the ideal perovskite structure with complete anion (O/H) disorder, while first-principles calculations suggested a possible 4844

DOI: 10.1021/acs.inorgchem.6b02834 Inorg. Chem. 2017, 56, 4840−4845

Article

Inorganic Chemistry

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DOI: 10.1021/acs.inorgchem.6b02834 Inorg. Chem. 2017, 56, 4840−4845