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Article

Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction

by
Toyoto Sato
1,*,
Shigeyuki Takagi
1,
Magnus H. Sørby
2,
Stefano Deledda
2,
Bjørn C. Hauback
2 and
Shin-ichi Orimo
1,3
1
Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
2
Institute for Energy Technology, P.O. Box 40, NO-2027 Kjeller, Norway
3
WPI-Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
*
Author to whom correspondence should be addressed.
Crystals 2018, 8(2), 89; https://doi.org/10.3390/cryst8020089
Submission received: 17 January 2018 / Revised: 5 February 2018 / Accepted: 7 February 2018 / Published: 9 February 2018
(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)
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Abstract

:
Aluminium-based complex hydrides (alanates) composed of metal cation(s) and complex anion(s), [AlH4]− or [AlH6]3− with covalent Al–H bonds, have attracted tremendous attention as hydrogen storage materials since the discovery of the reversible hydrogen desorption and absorption reactions on Ti-enhanced NaAlH4. In cases wherein alkaline-earth metals (M) are used as a metal cation, MAlH5 with corner-sharing AlH6 octahedron chains are known to form. The crystal structure of SrAlH5 has remained unsolved although two different results have been theoretically and experimentally proposed. Focusing on the corner-sharing AlH6 octahedron chains as a unique feature of the alkaline-earth metal, we here report the crystal structure of SrAlD5 investigated by synchrotron radiation powder X-ray and neutron diffraction. SrAlD5 was elucidated to adopt an orthorhombic unit cell with a = 4.6226(10) Å, b = 12.6213(30) Å and c = 5.0321(10) Å in the space group Pbcm (No. 57) and Z = 4. The Al–D distances (1.77–1.81 Å) in the corner-sharing AlD6 octahedra matched with those in the isolated [AlD6]3− although the D–Al–D angles in the penta-alanates are significantly more distorted than the isolated [AlD6]3−.

1. Introduction

Aluminium-based complex hydrides (alanates) composed of metal cation(s) (typically alkali or alkaline-earth metals) and a complex anion, [AlH4]− or [AlH6]3− with covalent Al–H bonds, have attracted tremendous attention as hydrogen storage materials since Bogdanović and Schwickardi reported the reversible hydrogen desorption and absorption reactions on Ti-enhanced NaAlH4 (Equation (1)) [1,2,3,4,5].
NaAlH4 ↔ 1/3Na3AlH6 + 2/3Al + H2 (g) ↔ NaH + Al + 1/2H2 (g)
NaAlH4 is composed of Na+ and [AlH4]−, and Na3AlH6 is composed of Na+ and [AlH6]3−; hereafter, these as referred to as Na tetra-alanates and Na hexa-alanates, respectively.
In addition to studies on NaAlH4 with Ti-based additives as hydrogen storage materials, exploratory studies on new alanates with different metal cations have also been conducted. Interestingly, alkaline-earth metal tetra-alanates M(AlH4)2 composed of an alkaline-earth metal (M) and [AlH4]− decompose into MAlH5 containing corner-sharing AlH6 octahedron chains [3,6,7,8,9] after releasing hydrogen from M(AlH4)2 (Equation (2)). We refer to MAlH5 as an alkaline-earth metal penta-alanate.
M(AlH4)2 → MAlH5 + Al + 3/2H2 (g)
Alanates with alkali metals, such as NaAlH4 [1,2,3,4,5], or mixed alkali and alkaline-earth metal cations, such as LiCa(AlH4)3 [10], do not form alanates with corner-sharing AlH6 octahedron chains. Therefore, the corner-sharing AlH6 octahedron chains are a unique feature of alanates composed of alkaline-earth metals. Although the crystal structures of CaAlH5 [6,7,8] and BaAlH5 [9] have been experimentally and theoretically identified, the structures of BeAlH5, MgAlH5 and SrAlH5 have so far not been experimentally proven. BeAlH5 and MgAlH5 may be difficult to form due to the small size of Be2+ and Mg2+. By contrast, SrAlH5 could be formed based on the size of the Sr2+. Indeed, two crystal structures for SrAlH5 have been theoretically and experimentally proposed by Klaveness et al. [7] and Pommerin et al. [11], respectively. Both crystal structures have similar orthorhombic unit cells with a ≈ 4.6 Å, b ≈ 5.0 Å and c ≈ 12.7 Å, but different space groups. The theoretically proposed crystal structure was adopted the space group P212121 (No. 19) with a BaAlF5-type crystal structure. The experimentally proposed crystal structure was described in space group Pnma (No. 62). Since the crystal structure reported by Pommerin et al. was studied using conventional powder X-ray diffraction, the positions of the hydrogen atom have not been determined. Even though P212121 is a subgroup of Pnma, the two proposed crystal structures give markedly different simulated powder X-ray diffraction patterns [11]. This demonstrates that they do not only differ with respect to inclusion of hydrogen but also have significantly different Sr–Al sublattice. Thus, the crystal structure of SrAlH5 remains unclarified. In the context of exploratory studies on new alanates, various Sr–Al hydrides with covalent Al–H bonds, including SrAlSiH [12], SrAl2H2 [12,13], Sr(AlH4)Cl [10] and Sr2AlH7 [14], have been reported. In the alanate family, Sr forms the most diverse set of Al-based (complex) hydrides with covalent Al–H bonds. For further understanding of alanates, a complete crystal structure determination of SrAlH5 would be indispensable.
Therefore, we here report the crystal structure of SrAlH5 using synchrotron radiation powder X-ray (SR-PXD) and powder neutron diffraction (PND) on isotopically labelled SrAlD5. Furthermore, we discuss the crystal structures of MAlH5, related alanates and Al-based hydrides with covalent Al–H distances viewed from dependences of metal cations.

2. Materials and Methods

SrAlD5 was synthesised by heat-treatment of mechanochemical milled SrD2 and AlD3 in the molar ratio 1:2 at 428 K for 1 h in Ar atmosphere of 0.1 MPa. SrD2 as the starting material was synthesised from dendritic pieces of Sr (Sigma-Aldrich, St. Louis, MO, USA, 99.99%) at 673 K for 10 h in a deuterium gas pressure of 0.5 MPa. AlD3 as the starting material was synthesised in diethyl ether according to the chemical reaction of LiAlD4 and AlCl3 [15,16]. The mixture of SrD2 and AlD3 was ball-milled at 400 r.p.m. under a deuterium gas pressure of 0.3 MPa using a Fritsch P7. The effective milling time was 3 h. Milling times of 15 min were alternated with pauses of 5 min duration, similar to our previous study [8,10,17].
SrAlD5 was initially measured using a conventional powder X-ray diffractometer (PXD, PANalytical X’PERT, Almelo, Netherlands, with Cu Kα radiation (wavelength λ = 1.5406 Å for Kα1 and 1.5444 Å for Kα2)) at room temperature. The sample for PXD was placed in a Lindemann glass capillary (outside diameter = 0.50 mm, thickness = 0.01 mm) and sealed with paraffin liquid for the PXD measurement with a transmission geometry at room temperature.
The high-resolution SR-PXD data of SrAlD5 were collected at room temperature at the Swiss-Norwegian beamlines (station BM01B) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The sample was placed in a rotating 0.5 mm borosilicate glass capillary. The wavelength of 0.5053 Å was obtained from a channel-cut Si (111) monochromator. Data were collected up to 40° in steps of 0.0065° in 2θ with 6 scintillator detectors fitted with analyser crystals.
The PND data of SrAlD5 were collected at 10 K and room temperature using the PUS instrument at the JEEP II reactor in Kjeller, Norway. The sample was placed in a cylindrical vanadium sample holder with a diameter of 6 mm. The wavelength of 1.5539 Å was obtained from a Ge (511) focusing monochromator. Data were collected from 10° to 130° and binned in steps of 0.05° in 2θ.
The PXD peaks of SrAlD5 were indexed by TREOR97 [18] to determine the initial unit cell parameters for the structural determinations. Crystal structure determinations of SrAlD5 with SR-PXD and PND data were performed combined with the ab initio structural determination programme FOX (version 1.9.0.2) [19] and the Rietveld programme GSAS with the graphical interface EXPGUI (version 1.80) [20]. FOX is used for determination of an initial crystal structure model and GSAS is used for the refinements of the initial crystal structure model. In the Rietveld analysis, the Pseudo-Voigt peak shape function with the Finger-Cox-Jephcoat asymmetry correction [21,22] was used. The background for SR-PXD and PND was modelled using the Chebyschev polynomial function in GSAS with 12 terms. Al–D distances in SrAlD5 were refined using a soft restraint, Al–D = 1.80 Å and Sr–D = 2.45 Å. Al and SrD2 were added as the impurity phases for the Rietveld refinement.
All samples were handled in Ar filled glove boxes with a dew point below 183 K and with less than 1 ppm of O2 to prevent (hydro-) oxidation.

3. Results

The synthesised sample, which was obtained from heat-treatment of mechanochemical milled SrD2 and AlD3 in the molar ratio of 1:2 at 428 K for 1 h in Ar atmosphere of 0.1 MPa, was characterised using conventional powder X-ray diffraction (Figure S1 in the Supplementary Material). Bragg peaks from metallic Al and unreacted SrD2 were easily identified. Al originated from AlD3 decomposition or the mechanochemical milled SrD2 + 2AlD3 since the presence of a complex anion, [AlD4]–, in the mechanochemical milled sample was identified by Raman spectroscopy. This confirms that Sr(AlD4)2 could be obtained from mechanochemical milling of SrD2 + 2AlD3 as reported in previous works [8,10,17] although the crystal structure of Sr(AlD4)2 could not be determined due to its poor crystallinity. The remaining Bragg peaks were indexed by an orthorhombic unit cell with a ≈ 4.66 Å, b ≈ 12.71 Å and c ≈ 5.03 Å, and these values are close to the theoretically and experimentally reported unit cell parameters of SrAlH5 [7,11]. Therefore, SrAlD5 is the main phase present in the synthesised sample (the differences between this study and the past studies will be addressed in detail in the discussion).
Considering the reflection conditions on the obtained orthorhombic unit cell, possible space groups were selected. Then, the ab initio structural determination programme FOX (version 1.9.0.2) [19] was performed on the orthorhombic unit cell with the selected space group and the SR-PXD and PND measured at room temperature for finding an initial crystal structure model for Rietveld refinement. All possible initial crystal structure models were attempted to be refined by the Rietveld programme GSAS with the graphical interface EXPGUI (version 1.80) [20]. Finally, the measured SR-PXD and PND patterns at room temperature are reasonably reproduced by SrAlD5 with a = 4.6226(10) Å, b = 12.6213(30) Å and c = 5.0321(10) Å in the space group Pbcm (No. 57) and Z = 4 (Figure 1a). The crystal structure is illustrated in Figure 1b. The crystallographic parameters are listed in Table 1. SrAlD5 was clarified to adopt corner-sharing AlD6 octahedron chains as the other penta-alanates. The inter-atomic distances of Al–D (1.77–1.81 Å) and Sr–D (2.46–3.04 Å) are listed in Table 2, which clearly shows that the both inter-atomic distances were reasonable compared with binary hydrides AlD3 [3] and SrD2 [23] or alanates and aluminium-based complex hydrides with AlD6 units [3] (discussed later).

4. Discussion

The different proposed crystal structure models and their simulated diffraction patterns are shown in Figure S2 in the Supplementary Material. All crystal structure models show orthorhombic unit cells but in different space groups. The crystal structure reported by Pommerin et al. shows a similar SR-PXD pattern as the one calculated using our crystal structure model despite the lack of hydrogen or deuterium atoms. This shows that the both metal atomic arrangements are nearly identical to our crystal structure model. By contrast, the crystal structure reported by Klaveness et al. neither fits with the SR-PXD nor PND from our crystal structure model. Attempts to refine the Pnma model from Pommerin et al. with our data, resulted in highly distorted AlD6 octahedra and poor fits to both SR-PXD and PND. The model and fits did not improve significantly by reducing the symmetry from Pnma (No. 62) to space group P212121 (No. 19) which is a subgroup of Pnma (No. 62). The PND pattern remained largely unchanged at 10 K (not shown). This indicates that SrAlD5 does not undergo any crystal structure transitions at lower temperatures. Therefore, SrAlD5 cannot be accurately represented by the space group Pnma (No. 62) nor the space group P212121 (No. 19), neither at room temperatures nor 10 K. The new model presented here is the most reasonable crystal structure for SrAlD5.
The crystal structure data for MAlD5 compounds (M: Ca, Sr, Ba) and the average Al–D, M–D and M–Al distances are listed in Table 3 [8,9]. The AlD6 octahedron chains in MAlD5 are illustrated in Figure 2. The average Al–D distances in MAlD5 are unaffected by the cation size. They are in the range of 1.75–1.80 Å whereas the average M–D or M–Al distances increase with increasing metal cation radius. Focusing on the AlD6 octahedron chains in MAlD5, the AlD6 octahedron, viewed along the AlD6 octahedron chains, appears qualitatively more canted as the metal cation radius decreases (Figure 2). Indeed, the ionic radius of Ca2+ is markedly smaller than Sr2+ and Ba2+ and CaAlD5 takes a more complex monoclinic structure with twice the number of formula units per unit cell compared to the orthorhombic SrAlD5 and BaAlD5. This suggests that BeAlH5 and MgAlH5 might be speculated to have low symmetry structures with large unit cells if BeAlH5 and MgAlH5 could be formed.
In the context of SrAlH5, Pommerin et al. also reported that EuAlH5 exhibited an isomorphic crystal structure similar to SrAlH5 in spite of the rare-earth metal [11]. This might originate into size and valence of cation metals because Eu2+ has close ionic radius to Sr2+ [24] and trivalent rare-earth metals do not yield the AlH6 octahedron chains but isolated AlH6 ([AlH6]3–) [25]. Although only EuAlH5 has been experimentally identified, divalent rare-earth metals with close ionic radius to Ca2+, Sr2+ and Ba2+ would be speculated to form penta-alanates such as EuAlH5.
Figure 3 shows the metal cation dependences on the average metal cation–Al and Al–D distances [3,8,9,10,12,13,14,25,26,27,28,29,30,31,32,33,34,35,36,37] in related alanates (deuterides) with covalent Al–D bonds. The average Al–D distances in corner-sharing AlD6 octahedra in MAlD5 are consistent with those found in hexa-alanates [3], Sr2AlD7 [14] and Ba2AlD7 [26]. However the D–Al–D angles in the penta-alanates (Table 3) are significantly more distorted than those in the compounds with isolated AlD6 octahedron. Thus the corner-sharing in the penta-alantes slightly affect the D–Al–D angles of the octahedron. Besides, the average Al–D distances were not affected by the metal cations (Al–D ≈ 1.60 Å ([AlD4]−), 1.80 Å ([AlD6]3− and AlD6 octahedron) and 1.75 Å (SrAlSiD and SrAl2D2)). By contrast, the average metal cation–Al distance was elongated with increasing metal cation radius. Interestingly, the average metal cation–Al distance in the penta-alanates and hexa-alanates was shorter than that with [AlD4]− in tetra-alanates, even though [AlD6]3− (AlH6 octahedron) has a bigger radius than [AlD4]– ([AlD4]−: 2.26 Å; [AlD6]3−: 2.56 Å [38]). Focusing on the ionic filling fractions (IFF) [10], as defined by the volumes of the crystal structure and the constituent ions in their ionic compounds including alanates, the average IFF for tetra-alanates and hexa-alanates are 0.72 and 0.79, respectively, indicating that hexa-alanates have tighter ionic (atomic) packing than tetra-alanates. This would explain the shorter average metal cation–Al distance with the [AlD6]3− (AlD6 octahedron) compared to that with [AlD4]−.

5. Conclusions

Focusing on the corner-sharing AlH6 octahedron chains as a unique feature of the alkaline-earth metal, we determined the crystal structure of SrAlD5, which adopted an orthorhombic unit cell with a = 4.6226(10) Å, b = 12.6213(30) Å and c = 5.0321(10) Å in the space group Pbcm (No. 57) and Z = 4, using synchrotron radiation powder X-ray and neutron diffraction. The crystal structure comprised corner-sharing AlD6 octahedron chains with Al–D = 1.76–1.81 Å.
Compared with the corner-sharing AlD6 octahedron chains in CaAlD5, SrAlD5 and BaAlD5 (penta-alanates), the structure and tilt of the AlD6 was observed to become more complex as the cation becomes smaller. If BeAlD5 and MgAlD5, which have not been experimentally identified, could be formed, they might have low symmetry structures with large unit cells.
Furthermore, the crystal structures of penta-alanates with corner-sharing AlD6 octahedron chains were compared with Al-based complex hydrides composed of metal cation(s) and complex anion(s), [AlD4]− and [AlD6]3−, as well as with Al-based hydrides with covalent Al–D bonds. The geometry of AlD6 octahedra in corner-sharing chains was found to be similar to isolated [AlD6]3− complex anions although the D–Al–D angles are distorted. In addition, the metal cation–Al distances shortened as the complex anion radius became larger (radius of [AlD6]3− > radius of [AlD4]−) although the Al–D distances were unaffected by the metal cations. This originates from the ionic filling fractions, according to which the hexa-alanates composed of metal cations and the [AlD6]3− complex anion have tighter ionic (atomic) packing crystal structures than the tetra-alanates composed of metal cations and the [AlD4]− complex anion.

Supplementary Materials

The following are available online at https://www.mdpi.com/2073-4352/8/2/89/s1, Figure S1: Conventional powder X-ray diffraction pattern of SrAlD5; Figure S2: (a) Simulated SR-PXD and PND patterns and (b) crystal structures of SrAlD5 on the present work and reported by Klaveness et al. and Pommerin et al.

Acknowledgments

We are grateful for the technical support from H. Ohmiya and N. Warifune. This research was supported by the JSPS KAKENHI Grant Numbers 16K06766, 16H06119 and 25220911 from MEXT, Japan, and Collaborative Research Center on Energy Materials in IMR (E-IMR), Institute for Materials Research, Tohoku University. The skillful assistance of the beamline personnel at the Swiss-Norwegian Beamlines at the European Synchrotron Radiation Facility (ESRF), Grenoble, France, is gratefully acknowledged.

Author Contributions

T.S. conceived this study, prepared and characterized the samples, analyzed the SR-PXD and the PND data, determined the crystal structure and wrote the manuscript; S.T. determined the crystal structure; M.H.S., S.D. and B.C.H. performed the SR-PXD and the PND; S.O. designed and conducted the project.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Bogdanović, B.; Schwickardi, M. Ti-doped alkali metal aluminium hydrides as potential novel reversible hydrogen storage materials. J. Alloy. Compd. 1997, 253–254, 1–9. [Google Scholar] [CrossRef]
  2. Orimo, S.; Nakamori, Y.; Eliseo, R.J.; Züttel, A.; Jensen, C.M. Complex hydrides for hydrogen storage. Chem. Rev. 2007, 107, 4111–4132. [Google Scholar] [CrossRef] [PubMed]
  3. Hauback, B. Structures of aluminium–based light weight hydrides. Z. Krist. 2008, 223, 636–648. [Google Scholar] [CrossRef]
  4. Eberle, U.; Felderhoff, M.; Schüth, F. Chemical and physical solutions for hydrogen storage. Angew. Chem. Int. Ed. 2009, 48, 6608–6630. [Google Scholar] [CrossRef] [PubMed]
  5. Graetz, J.; Hauback, B.C. Recent developments in aluminum–based hydrides for hydrogen storage. MRS Bull. 2013, 38, 473–479. [Google Scholar] [CrossRef]
  6. Weidenthaler, C.; Frankcombe, T.J.; Felderhoff, M. First crystal structure studies of CaAlH5. Inorg. Chem. 2006, 45, 3849–3851. [Google Scholar] [CrossRef] [PubMed]
  7. Klaveness, A.; Vajeeston, P.; Ravindran, P.; Fjellvåg, H.; Kjekshus, A. Structure and bonding in BAlH5 (B = Be, Ca, Sr) from first–principle calculations. J. Alloy. Compd. 2007, 433, 225–232. [Google Scholar] [CrossRef]
  8. Sato, T.; Sørby, M.H.; Ikeda, K.; Sato, S.; Hauback, B.C.; Orimo, S. Syntheses, crystal structures, and thermal analyses of solvent–free Ca(AlD4)2 and CaAlD5. J. Alloy. Compd. 2009, 487, 472–478. [Google Scholar] [CrossRef]
  9. Zhang, Q.-A.; Nakamura, Y.; Oikawa, K.; Kamiyama, T.; Akiba, E. New alkaline earth aluminum hydride with one–dimensional zigzag chains of [AlH6]: Synthesis and crystal structure of BaAlH5. Inorg. Chem. 2002, 41, 6941–6943. [Google Scholar] [CrossRef] [PubMed]
  10. Sato, T.; Takagi, S.; Deledda, S.; Hauback, B.C.; Orimo, S. Goldschmidt tolerance factor to arbitrary ionic compounds. Sci. Rep. 2016, 6, 23592. [Google Scholar] [CrossRef] [PubMed]
  11. Pommerin, A.; Wosylus, A.; Felderhoff, M.; Schüth, F.; Weidenthaler, C. Synthesis, crystal structures, and hydrogen-storage properties of Eu(AlH4)2 and Sr(AlH4)2 and of their decomposition intermediates, EuAlH5 and SrAlH5. Inorg. Chem. 2012, 51, 4143–4150. [Google Scholar] [CrossRef] [PubMed]
  12. Björling, T.; Noréus, D.; Jansson, K.; Andersson, M.; Leonova, E.; Edén, M.; Hålenius, U.; Häussermann, U. SrAlSiH: A polyanionic semiconductor hydride. Angew. Chem. Int. Ed. 2005, 44, 7269–7273. [Google Scholar] [CrossRef] [PubMed]
  13. Gingl, F.; Vogt, T.; Akiba, E. Trigonal SrAl2H2: The first Zintl phase hydride. J. Alloy. Compd. 2000, 306, 127–132. [Google Scholar] [CrossRef]
  14. Zhang, Q.-A.; Nakamura, Y.; Oikawa, K.; Kamiyama, T.; Akiba, E. Synthesis and crystal structure of Sr2AlH7: A new structural type of alkaline earth aluminum hydride. Inorg. Chem. 2002, 41, 6547–6549. [Google Scholar] [CrossRef] [PubMed]
  15. Brower, F.M.; Matzek, N.E.; Reigler, P.F.; Rinn, H.W.; Roberts, C.B.; Schmidt, D.L.; Snover, J.A.; Terada, K. Preparation and properties of aluminum hydride. J. Am. Chem. Soc. 1976, 98, 2450–2453. [Google Scholar] [CrossRef]
  16. Ikeda, K.; Muto, S.; Tatsumi, K.; Menjo, M.; Kato, S.; Bielmann, M.; Züttel, A.; Jensen, C.M.; Orimo, S. Dehydriding reaction of AlH3: In situ microscopic observations combined with thermal and surface analysis. Nanotechnology 2009, 20, 204004. [Google Scholar] [CrossRef] [PubMed]
  17. Sato, T.; Ikeda, K.; Li, H.-W.; Yukawa, H.; Morinaga, M.; Orimo, S. Direct dry syntheses and thermal analyses of a series of aluminum complex hydrides. Mater. Trans. 2009, 50, 182–186. [Google Scholar] [CrossRef]
  18. Werner, P.-E.; Eriksson, L.; Westdahl, M. TREOR, a semi-exhaustive trial-and-error powder indexing program for all symmetries. J. Appl. Crystallogr. 1985, 18, 367–370. [Google Scholar] [CrossRef]
  19. Favre-Nicolin, V.; Černý, R. FOX, ‘Free objects for crystallography’: A modular approach to ab initio structure determination from powder diffraction. J. Appl. Crystallogr. 2002, 35, 734–743. [Google Scholar] [CrossRef]
  20. Toby, B.H. EXPGUI, a graphical user interface for GSAS. J. Appl. Crystallogr. 2001, 34, 210–213. [Google Scholar] [CrossRef]
  21. Van Laar, B.; Yelon, W.B. The peak in neutron powder diffraction. J. Appl. Crystallogr. 1984, 17, 47–54. [Google Scholar] [CrossRef]
  22. Thompson, P.; Cox, D.E.; Hastings, J.B. Rietveld refinement of Deby-Scherrer synchrotron X-ray data from Al2O3. J. Appl. Crystallogr. 1987, 20, 79–83. [Google Scholar] [CrossRef]
  23. Brese, N.E.; O’Keeffe, M.; Von Dreele, R.B. Synthesis and crystal structure of SrD2 and SrND and bond valence parameters for hydrides. J. Solid State Chem. 1990, 88, 571–576. [Google Scholar] [CrossRef]
  24. Shannon, R.D. Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Cryatallogr. A 1976, 32, 751–767. [Google Scholar] [CrossRef]
  25. Weidenthaler, C.; Pommerin, A.; Felderhoff, M.; Sun, W.; Wolverton, C.; Bogdanović, B.; Schüth, F. Complex rare-earth aluminum hydrides: Mechanochemical preparation, crystal structure and potential for hydrogen storage. J. Am. Chem. Soc. 2009, 131, 16735–16743. [Google Scholar] [CrossRef] [PubMed]
  26. Zhang, Q.A.; Nakamura, Y.; Oikawa, K.; Kamiyama, T.; Akiba, E. Hydrogen–induced phase decomposition of Ba7Al13 and the crystal structure of Ba2AlH7. J. Alloy. Compd. 2003, 361, 180–186. [Google Scholar] [CrossRef]
  27. Hauback, B.C.; Brinks, H.W.; Fjellvåg, H. Accurate structure of LiAlD4 studied by combined powder neutron and X-ray diffraction. J. Alloy. Compd. 2002, 346, 184–189. [Google Scholar] [CrossRef]
  28. Hauback, B.C.; Brinks, H.W.; Jensen, C.M.; Murphy, K.; Maeland, A.J. Neutron diffraction structure determination of NaAlD4. J. Alloy. Compd. 2003, 358, 142–145. [Google Scholar] [CrossRef]
  29. Hauback, B.C.; Brinks, H.W.; Heyn, R.H.; Blom, R.; Fjellvåg, H. The crystal structure of KAlD4. J. Alloy. Compd. 2005, 394, 35–38. [Google Scholar] [CrossRef]
  30. Fossdal, A.; Brinks, H.W.; Fichtner, M.; Hauback, B.C. Determination of the crystal structure of Mg(AlH4)2 by combined X-ray and neutron diffraction. J. Alloy. Compd. 2005, 387, 47–51. [Google Scholar] [CrossRef]
  31. Grove, H.; Brinks, H.W.; Heyn, R.H.; Wu, F.-J.; Opalka, S.M.; Tang, X.; Laube, B.L.; Hauback, B.C. The structure of LiMg(AlD4)3. J. Alloy. Compd. 2008, 455, 249–254. [Google Scholar] [CrossRef]
  32. Brinks, H.W.; Hauback, B.C. The structure of Li3AlD6. J. Alloy. Compd. 2003, 354, 143–147. [Google Scholar] [CrossRef]
  33. Rönnebro, E.; Noréus, D.; Kadir, K.; Reiser, A.; Bogdanovic, B. Investigation of the perovskite related structures of NaMgH3, NaMgF3 and Na3AlH6. J. Alloy. Compd. 2000, 299, 101–106. [Google Scholar] [CrossRef]
  34. Grove, H.; Brinks, H.W.; Løvvik, O.M.; Heyn, R.H.; Hauback, B.C. The structure of LiMgAlD6 from combined neutron and synchrotron X-ray powder diffraction. J. Alloy. Compd. 2008, 460, 64–68. [Google Scholar] [CrossRef]
  35. Brinks, H.W.; Hauback, B.C.; Jensen, C.M.; Zidan, R. Synthesis and crystal structure of Na2LiAlD6. J. Alloy. Compd. 2005, 392, 27–30. [Google Scholar] [CrossRef]
  36. Sørby, M.H.; Brinks, H.W.; Fossdal, A.; Thorshaug, K.; Hauback, B.C. The crystal structure and stability of K2NaAlH6. J. Alloy. Compd. 2006, 415, 284–287. [Google Scholar] [CrossRef]
  37. Lee, M.H.; Börling, T.; Hauback, B.C.; Utsumi, T.; Moser, D.; Bull, D.; Noréus, D.; Sankey, O.F.; Häussermann, U. Crystal structure, electronic structure, and vibrational properties of MAlSiH (M = Ca,Sr,Ba): Hydrogenation-induced semiconductors from the AlB2-type alloys MAlSi. Phys. Rev. B 2008, 78, 195209. [Google Scholar] [CrossRef]
  38. Jenkins, H.D.B.; Thakur, K.P. Reappraisal of thermochemical radii for complex ions. J. Chem. Educ. 1979, 56, 576–577. [Google Scholar] [CrossRef]
Crystals 08 00089 g001 550
Figure 1. (a) The Rietveld refinement fits of (upper) SR-PXD (Rwp = 0.0306) with λ = 0.5053 Å and (lower) PND (Rwp = 0.0429) with λ = 1.5539 Å for SrAlD5 and (b) the crystal structure of SrAlD5 viewed along the a-axis (upper) and c-axis (lower). Purple, yellow and blue spheres and light–green octahedra represent Sr, Al, D and AlD6, respectively. In the Rietveld refinement fits of SR-PXD and PND, the observed, calculated background and difference between observed and calculated patterns are indicated with circles, a red, green and blue lines, respectively. The Bragg reflection positions are shown for (top) SrAlD5, (middle) Al and (bottom) SrD2. The refined weight fractions of SrAlD5, Al and SrD2 were 75 wt % (84 wt %), 20 wt % (13 wt %) and 5 wt % (3 wt %), respectively (PND are provided in parentheses).
Figure 1. (a) The Rietveld refinement fits of (upper) SR-PXD (Rwp = 0.0306) with λ = 0.5053 Å and (lower) PND (Rwp = 0.0429) with λ = 1.5539 Å for SrAlD5 and (b) the crystal structure of SrAlD5 viewed along the a-axis (upper) and c-axis (lower). Purple, yellow and blue spheres and light–green octahedra represent Sr, Al, D and AlD6, respectively. In the Rietveld refinement fits of SR-PXD and PND, the observed, calculated background and difference between observed and calculated patterns are indicated with circles, a red, green and blue lines, respectively. The Bragg reflection positions are shown for (top) SrAlD5, (middle) Al and (bottom) SrD2. The refined weight fractions of SrAlD5, Al and SrD2 were 75 wt % (84 wt %), 20 wt % (13 wt %) and 5 wt % (3 wt %), respectively (PND are provided in parentheses).
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Crystals 08 00089 g002 550
Figure 2. Corner-sharing AlD6 octahedron chains viewed from (left) along and (right) perpendicular to the chains in (a) CaAlD5, (b) SrAlD5 and (c) BaAlD5 (Al: yellow sphere; D: blue sphere).
Figure 2. Corner-sharing AlD6 octahedron chains viewed from (left) along and (right) perpendicular to the chains in (a) CaAlD5, (b) SrAlD5 and (c) BaAlD5 (Al: yellow sphere; D: blue sphere).
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Crystals 08 00089 g003 550
Figure 3. Metal cation dependences on (upper) average metal cation–Al and (lower) Al–D distances in alanates and related Al-based hydrides. The distances were obtained from their deuterides, except for Mg(AlH4)2, LiCa(AlH4)3, LiCaAlH6, K2NaAlH6, LaAlH6, CeAlH6, PrAlH6 and NdAlH6 (LiCa(AlH4)3 and LiCaAlH6 are theoretical calculation results) [3,8,9,10,12,13,14,25,26,27,28,29,30,31,32,33,34,35,36,37] because their crystal structural investigations on deuterides have not been reported. Average metal cation–Al distance of Na3AlD6 (3.65 Å) [33] is overlapped with NaAlD4 (3.66 Å) [28]. In CaAlSiD, SrAlSiD, BaAlSiD and SrAl2D2, Ca, Sr and Ba were formally considered as their metal cation.
Figure 3. Metal cation dependences on (upper) average metal cation–Al and (lower) Al–D distances in alanates and related Al-based hydrides. The distances were obtained from their deuterides, except for Mg(AlH4)2, LiCa(AlH4)3, LiCaAlH6, K2NaAlH6, LaAlH6, CeAlH6, PrAlH6 and NdAlH6 (LiCa(AlH4)3 and LiCaAlH6 are theoretical calculation results) [3,8,9,10,12,13,14,25,26,27,28,29,30,31,32,33,34,35,36,37] because their crystal structural investigations on deuterides have not been reported. Average metal cation–Al distance of Na3AlD6 (3.65 Å) [33] is overlapped with NaAlD4 (3.66 Å) [28]. In CaAlSiD, SrAlSiD, BaAlSiD and SrAl2D2, Ca, Sr and Ba were formally considered as their metal cation.
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Table
Table 1. Crystallographic parameters for SrAlD5 with a = 4.6226(10) Å, b = 12.6213(30) Å and c = 5.0321(10) Å obtained from both of SR-PXD and PND in the space group Pbcm (No. 57) and Z = 4. The Uiso of Al was not refined and the occupancies of each atomic position were fixed as 1.00. Estimated standard deviations are in parentheses.
Table 1. Crystallographic parameters for SrAlD5 with a = 4.6226(10) Å, b = 12.6213(30) Å and c = 5.0321(10) Å obtained from both of SR-PXD and PND in the space group Pbcm (No. 57) and Z = 4. The Uiso of Al was not refined and the occupancies of each atomic position were fixed as 1.00. Estimated standard deviations are in parentheses.
AtomWyckoff Positionxyz100 × Uiso (Å2)
Sr4d0.2532(7)0.8925(3)0.25000.13(3)
Al4d0.3296(11)0.1597(3)0.25001.00
D14c0.4366(13)0.25000.00004.75(15)
D24d0.3461(13)0.5790(5)0.25004.75(15)
D34d0.0311(13)0.7146(3)0.25004.75(15)
D48e0.1914(7)0.0718(3)0.4986(9)4.75(15)
Table
Table 2. Inter-atomic distances of SrAlD5. Estimated standard deviations are in parentheses.
Table 2. Inter-atomic distances of SrAlD5. Estimated standard deviations are in parentheses.
Inter-Atomic Distances (Å)
Sr–D12.621(4) × 2
Sr–D22.5776(19) × 2
2.996(7)
Sr–D32.4686(24)
3.035(4) × 2
Sr–D42.4549(17) × 2
2.602(4) × 2
2.898(5) × 2
Al–D11.7683(30) × 2
Al–D21.812(5)
Al–D31.806(4)
Al–D41.7901(29) × 2
Table
Table 3. Crystal structure data for MAlD5 and selected inter-atomic distances and angles (Estimated standard deviations for SrAlD5 are in parentheses).
Table 3. Crystal structure data for MAlD5 and selected inter-atomic distances and angles (Estimated standard deviations for SrAlD5 are in parentheses).
Crystal System (Space Group)Unit Cell ParametersZAvg. Al–D DistancesD–Al–D AnglesAvg. M–D DistancesAvg. M–Al Distances
CaAlD5 [8]Monoclinic (P21/c)a = 9.800 Å
b = 6.908 Å
c = 12.450 Å
β = 137.94°
V = 564.69 Å3		81.75 Å78.0°–101.8°
166.6°–177.9°		2.43 Å3.50 Å
SrAlD5 (present result)Orthorhombic (Pbcm)a = 4.6226(10) Å
b = 12.6213(30) Å
c = 5.0321(10) Å
V = 293.59(12) Å3		41.79(2) Å84.7(2)°–97.5(3)°
168.4(3)°–175.3(3)°		2.70(21) Å3.55(26) Å
BaAlD5 [9]Orthorhombic (Pna21)a = 9.194 Å
b = 7.040 Å
c = 5.106 Å
V = 330.51 Å3		41.77 Å75.7°–103.7°
161.4°–169.9°		2.82 Å3.68 Å

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Sato, T.; Takagi, S.; Sørby, M.H.; Deledda, S.; Hauback, B.C.; Orimo, S.-i. Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction. Crystals 2018, 8, 89. https://doi.org/10.3390/cryst8020089

AMA Style

Sato T, Takagi S, Sørby MH, Deledda S, Hauback BC, Orimo S-i. Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction. Crystals. 2018; 8(2):89. https://doi.org/10.3390/cryst8020089

Chicago/Turabian Style

Sato, Toyoto, Shigeyuki Takagi, Magnus H. Sørby, Stefano Deledda, Bjørn C. Hauback, and Shin-ichi Orimo. 2018. "Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction" Crystals 8, no. 2: 89. https://doi.org/10.3390/cryst8020089

APA Style

Sato, T., Takagi, S., Sørby, M. H., Deledda, S., Hauback, B. C., & Orimo, S.-i. (2018). Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction. Crystals, 8(2), 89. https://doi.org/10.3390/cryst8020089

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