Experimental studies of complex hydride YMn2H6 on formation
kinetics and X-ray absorption fine structure analyses
Motoaki Matsuo,1 Daiju Matsumura,2 Yasunori Nishihata,2 Guanqiao Li,1
Nao Hiyama,1 and Shin-ichi Orimo1
1Institute
for Materials Research, Tohoku University, Katahira 2-1-1, Sendai, 980-8577, Japan,
2Quantum
Beam Science Directorate, Japan Atomic Energy Agency, Hyogo 679-5148, Japan
Supporting Information
Detailed Analytical Method for EXAFS of YMn2H6
Background subtraction of EXAFS spectra were performed by IFEFFIT code.#1 The Rbkg
parameter in IFEFFIT code was set to 0.8 in order to protect the Mn-H peak which appears around
1.3 Å in Fourier transform intensity. EXAFS spectra were analyzed by using FEFF9 code.#2 The
crystal structure determined from the neutron diffraction technique was applied as the standard
function for fitting.#3 FEFF9 code was used with the self-consistent field calculation. Mn/Y
substitutional random occupation of 8c sites was expressed by taking average of Mn only occupation
and Y only occupation. All coordination numbers were set to the value of crystal structure
determined from the neutron diffraction technique.S3 Energy shift was unified in each site and used
as free parameter. Interatomic distance and Debye-Waller factor of each shell were used as free
parameter. Multiple scattering in straight atomic coordination was considered only in
Mn1(8c)–H–Mn1/Y(8c) path. Fitting procedure was performed in R-space with Δk = 2.5−10 Å-1, ΔR
= 1−4.8 Å. kn-weight for Fourier transform was set to k1 in order to enhance the hydrogen backward
scattering at low k region as described later. Intrinsic loss factor was set to free parameter and
determined to 0.87. Edge shift values ∆E were determined to -8.7(25) eV for Mn1–H, Mn1–Mn2(4a)
and Mn1–Mn1/Y and -4.3(45) eV for Mn2–H, Mn2–Mn1/Y and Mn2–Mn2 paths. R-factor was
defined as
 (k
i
data
i
(k )  k i fit (k )) 2
 k
data
i
(k ) 2 and obtained to be 0.02.
i
Validity of Assigned Mn2–H Bonding Contribution
In the case of YMn2H6, as shown in Fig. S1, EXAFS function χ(k) for Mn2−H has sufficiently
observable intensity which is comparable to those for Mn2−Y/Mn1 and Mn2−Mn2 in the low
wavenumber k region because the Mn2 atoms bind covalently to as many as six nearest neighboring
H atoms to form [MnH6]5− complex anions. In consideration of the large χ(k) intensity for Mn2−H at
low k region, we adopted not k3-weighted but k1-weighted factor to obtain Fourier transform
intensity. As shown in Fig. S2(a), the Mn2−H contribution is more stressed for the k1-weighted case,
indicating that appropriate selection of kn-weighted factor is key for the analysis. Furthermore,
relatively small Debye-Waller factor due to the weak thermal vibration in the bonding direction in
the [MnH6]5− complex anions at room temperature makes the bonding contribution more observable
(See Table I in the manuscript). We also confirmed that the contribution at low interatomic distances
S1
(1−1.5 Å) is not attributed to the background, which is often discussed in EXAFS studies, from the
fact that the intensities at low distances for the experimental data of YMn2 and YMn2H4.5 are
actually much smaller than that of YMn2H6 as shown in Fig. S2(b).
EXAFS function, (k)
0.1
Mn2-H
Mn2-Y/Mn1
Mn2-Mn2
0.0
-0.1
4
6
Wavenumber, k (1/Å)
8
10
Figure S1 Simulated EXAFS functions χ(k) for Mn2−H, Mn2−Y/Mn1 and Mn2−Mn2 of YMn2H6.
(a)
(b)
3
Fourier transform intensity (a. u.)
Fourier transform intensity (a. u.)
YMn2
k weight
40
20
0
2
k weight
6
3
0
1
k weight
1
YMn2H4.5
YMn2H6
0
0
Figure S2
1
2
3
4
5
Interatomic distance, R (Å)
6
0
1
2
3
4
5
Interatomic distance, R (Å)
6
(a) Simulated Fourier transform intensities for total Mn site (Mn1+Mn2) with different
n
k -weighted factors and (b) experimental Fourier transform intensities of YMn2, YMn2H4.5 and YMn2H6.
References
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(#2) A.L. Ankudinov, B. Ravel, J.J. Rehr, and S.D. Conradson, Phys. Rev. B 58, 7565 (1998).
(#3) V. Paul-Boncour, S.M. Filipek, M. Dorogova, F. Bourée, G. André, I. Marchuk, A.
Percheron-Guégan, and R.-S. Liu, J. Solid State Chem. 178, 356 (2005).
S2