Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

1B, 4B2/2005G145

Application of resonant X-ray diffraction for investigation of crystal and bandstructures of sulfide photocatalysts derived from ZnS with isovalent substitutions
V. PETRYKIN*1, K. TOMITA1, M. KAKIHANA1, Y. SHIMODAIRA2, A. KUDO2,3,4,54
H. SAWA , T. KAKIUCHI
1

IMRAM, Tohoku Univ., Katahira 2-1-1, Aoba-ku, Sendai 980-8577 JapanTokyo Univ. of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
3CREST, JST, 4-1-8 Honcho, Kawaguchi-shi, Saitama 332-0012, Japan
4Photon Factory, High Energy Research Organization, Oho, Tsukuba, Ibaraki 305-0801, Japan
5Dept. of Materials Structure Science, Graduate Univ. for Advanced Studies, 305-0801, Japan
2Introduction
The materials capable of converting solar energy into
chemical energy attract a lot of attention. It was reported
recently that solid solutions in ZnS-CuInS2-AgInS2
system exhibit high photocatalytic activity for hydrogenproduction under visible light irradiation in the presenceof sacrificial reagents [1]. In this work, a series of newchalcogenide photocatalytic materials Ag2ZnSnS4,Ag2ZnGeS4, Cu2ZnSnS4, and Cu2ZnGeS4 were studied.
Although Rietveld refinement using conventional
diffraction patterns gives quite reasonable metal-sulfur
interatomic distances, further discussion of possible
disorder in Ag-Sn, Zn-Cu, Zn-Ge, Zn-Cu-Ge sites is
impossible due to close X-ray scattering factors of theseelements. The objective of this proposal is to use
synchrotron radiation for resonance diffraction near Zn-,Cu- and Ge-K absorption edges, which can provide theunambiguous characterization of real structure of thesulfides. During the first stage of the project, BL-1B
beam line was used to collect part of the planed fulldataset. The rest of the data will be collected at BL-4B2
considering the results of preliminary analysis.

BL-1B diffractometer was sufficient forstructural characterization of this compound.

accurate

Results
Cu2ZnSnS4 was found to have stannite type structure(a=5.43267Å, c=10.84395(13)Å, I-42m Zn (0,0,0),Cu(0,1/2,1/4), Sn(1/2,1/2,0), S(0.7532(3), 0.7532(3),0.8693(2))). Interatomic distances of 2.3676(24)Å (Zn-S),
2.4070(24) Å (Sn-S) and 2.3157(15) Å (Cu-S) allow
estimation of bond-valence sums [3] to be 1.86 for Zn,
3.92 for Sn and 1.29 Cu. The high deviation from thevalence of Cu can not be explained by the experimental
uncertainty. Thus, one should conclude that Zn can substitute for Cu. The unrestrained refinement of occupanciesof metal sites yielded relatively large standard deviations.
The variation of occupancies in the refined model resulted
in the total Rwp values for joint refinement as shown inFig. 1. One may notice a flat bottom in the range ofconcentrations ~0.35-0.45, which is responsible for large
standard deviations of occupancies. Examination of therefinement results also suggests that substitution into Snsite is unlikely.
2.85
2.80
Total Rwp, %Experiment
Powder diffraction data were collected at room
temperature using Debye-Scherrer camera equipped withimaging plate detector at BL-1B beam station. Ag2ZnSnS4,Ag2ZnGeS4, Cu2ZnSnS4, and Cu2ZnGeS4 were carefully
ground and packed into the 0.1-0.3 mm glass capillarytubes. Up to four datasets were acquired using 1.38255 Å(Cu-K edge) 1.28642Å (Zn-K edge), 1.11868 Å (Ge-Kedge) and 0.70015Å wavelength of the incident X-ray
beam. Actual values of wavelength were refined usingreference diffraction patterns collected for standard CeO2
samples. The obtained diffraction patterns of the sulfides
were combined for each sample and used for joint
refinement of in total three or four patterns for eachsample by GSAS package [2]. The f’ and f” values ofelements at different wavelengths were calculated byFPRIME program included in GSAS package. Absorption
correction was made for cylindrical shape assuming 60%
packing density. In this report we will focus only on
Cu2ZnSnS4 because dataset collected at this stage using

2.75
2.70
2.65
2.60
2.55
0.0

0.1

0.2

0.3

0.4

0.5

[Cu(1-x)Znx]2[Zn1-2xCu2x]SnS4, x

Fig. 1. Final Rwp values vs. disorder parameter x inthe [Cu(1-x)Znx]2[Zn1-2xCu2x]SnS4 model. in joint
refinement of Zn-, Cu-K edge and 0.7A data set.
References[1] I. Tsuji et al., Angew. Chem. 44, 3565 (2005).
[2] A.C. Larson and R.B. Von Dreele Los Alamos
National Laboratory Report LAUR 86-748 (2000).
[3] I.D. Brown, D. Altermatt Acta Cryst. B41, 244(1985)* valery@tagen.tohoku.ac.jp

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