Ionic conductivities were investigated for hydrous and anhydrous H4Ge4S10 and H2Ge4S9 thiogermanic acids. The hydrous phases, denoted as H4Ge4S10·xH2O (7 > x > 9), were superprotonic conductors. Proton conductivity and thermal stability were dependent on the Ge4S104− cage structure. Two distinct structural units, adamantane-like and a unique more complex cage unit, were produced in both the hydrous and anhydrous phases. The composition and structure of these phases were analyzed in terms of Raman, infrared, mass and thermogravimetric data. Ionic conductivity values of 10−10 to 10−3S/cm were determined from ac impedance measurements of the hydrous thiogermanic acids in the range of −55 to 125C. Conductivity values of 10−10 to 10−7S/cm were recorded for the corresponding anhydrous phases between 180 and 500C. The fast ionic conductivity of the hydrous phases was consistent with loosely bound water, whereas the conductivity of the anhydrous phases was correlated to the presence of thiol (S–H) groups. At higher temperatures these groups were observed to thermally decompose to hydrogen sulfide.

Proton Conductivity in Hydrous and Anhydrous Thiogermanic Acids. S.A.Poling, C.R.Nelson, J.T.Sutherland, S.W.Martin: Solid State Ionics, 2004, 170[1-2], 43-9