Decoupage du ternaire ytterbium-indium-soufre description cristallographique des phases presentes

In the ternary Yb-In-S system two phases were identified and their structure determinated on single crystal by X-ray diffraction. Yb[sub 4/3]In[sub 4/3]S[sub 4] belongs to a solid solution, it has a cubic structure intermediate between spinel and NaCl type. All metal sites are incompletely occupied. Yb[sub 18]In[sub 7.33]S[sub 36] is hexagonal. Yb[sup III] atoms have two types of environment with sevenfold prismatic and sixfold octahedral coordination. However, the octahedral sites are occupied also by In[sup III] atoms. Large channels around the threefold and sixfold axes are occupied by In[sup 1] or are empty. The two structures are analyzed. They have the particularity to have octahedral sites occupied by Yb[sup III] and In[sup III] statistically disordered. The most similar radii of Yb[sup III] and In[sup III] atoms are likely the reason of the existence of the hexagonal phase not found for other rare earth atoms and also of the presence of a large solid solution, domain for the first phase.