Un nouveau matériau, Ag9GaSe6: Etude structurale de la phase α

α-Ag9 GaSe6 is cubic, space group F43m, with a = 11.126(2) Å and Z = 4. The diffraction pattern at 20°C using MoKα radiation was collected with an automatic four-circle diffractometer. The structure was determined by beginning from the low-temperature structure (βAg9GaSe6). An anisotropic full-matrix least-squares refinement was performed yielding a final R of 0.063 for the 103 reflections actually measured. The four Ga atoms and eight Se atoms are located on a 16(e) position. All the GaSe bonds are 2.366(10) Å. The Ag atoms are equally distributed on three sets of positions: two 48(h) and one 96(i). Among the 36 Ag atoms, 24 are bound to 3 Se atoms in an almost planar triangular arrangement (2.43(4) < AgSe bonds < 2.85(7) Å), and 12 are in a tetrahedron of 4 Se atoms (2.68(5) < AgSe bonds < 2.93(5) Å).