Environmental Science and Technology, Niigata University Graduate School of Science and Technology^* Faculty of Science, Niigata University,Japan^**
○Yuu Yanadori^* Yo Otaki^* Yuusuke Seki^* Shoji Kashida^**

Ga₂Se₃ has a zinc-blende type structure, where in order to satisfy the valence condition, one-third of the cation sites is vacant. From X-ray powder diffraction study, the vacancy ordered phase, β-Ga₂Se₃ is reported to have a monoclinic structure, a=6.6608, b=11.6516, c=6.6491A, and β=108.840 (Z=4). In this study using single crystal samples we have performed X-ray structural analysis.
The X-ray precession photographs show zinc-blende type main reflections and weak reflections at 1/3(220)c, 1/6(111)c, where c means the ideal cubic lattice. Diffuse streaks are also observed which is centered on main Bragg peaks and elongated along the <111> direction. From the reciprocal unit cell vectors, a^*=(1-11)c, b^*=2/3(1-10)c and c^*=1/6(111)c, we concluded that the crystal is triclinic a=1/2(-1-12)c, b=3/2(10-1)c, c=3(110)c, α=60.0465, β=125.285 and γ=149.97 (Z=6).
Intensity data were collected on Huber four-circle diffractmeter, and the structure analysis was done using the heavy-atom method. Since the crystal is composed of multiple twins, we have used only the satellite reflections. The synthesized partial Patterson function shows that three of the six vacant cation sites are located along the (011) axis (Fig. 1).