Cation-deficient Quaternary Thiospinels

Ashok K. Canguli, Shalabh Cupta and Cunjan Carg 

In general, spinel and other chalcogen-based thiospinels with Z=8 leads to the total unit cell content of 8 and 16 (8 a and 16 d sites) cations and 32 anions in the 32 e site corresponding to the formula A8B15O32. In spinels, the AX4 tet-rahedra share comers with BXg octahedra and the octahedra are Hnked together by sharing edges (Fig. 15.1). 

The synthesis of quaternary thiospinels, like Ag2FeSn3Sg [5], Ag2MnSn3Sg [6], and Cu2NiSn3Sg [7], has been achieved by reacting metals along with sulfur powder in an evacuated silica tube. Pure phases of these compounds were obtained at 750 °C, 670 °C and 750 °C respectively. 

Apart from the above-mentioned ternary thiospinels, more complex spinels (quaternary thiospinels) belonging to the formula CugM4Sni2S32 or Cu2MSn3Sg (M = Ni, Fe, Co, Mn) are also known in the literature for Li-ion intercalation [14]. 

Recently lithium insertion in quaternary thiospinels like (Cug.giGeDg.ggjga [Fe4Sni2]i6dS32 and (Cu4.xGen3o+x)8a[Co4Sni2]i6dS32 have been reported [15, 16]. It is believed that the vacancies in the tetrahedral 8 a sites result from a topotac-tic substitution of four Cu ions by one Ge ion. 

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These studies show that the thiospinel structure is quite flexible with opportunity for cation vacancies at the 8 a site. Our investigation on such cation-deficient thiospinels is significant in that it shows that additional vacancies are possible in the 8 a site. Most of the cation-deficient compounds known earlier (predominantly copper compounds) were obtained by extraction of Cu by using various oxidizing reagents. These studies show that such cation-deficient quaternary thiospinels can also be obtained by direct solid-state reactions. 

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