Ionic conductivities were investigated for mixed H alkali thiogermanates possessing the adamantane-like Ge4S104− structural complex anion. Anhydrous compounds of the form HxM4−xGe4S10 (M = K and Rb) and HxCs4−xGe4S10·yH2S for 0 ≤ x ≤ 4 and 0 ≤ y ≤ 1 were synthesized by using a novel preparation method involving reacting the respective alkali thiogermanate glass or adamantane-like crystalline phase with liquid hydrogen sulfide. The reaction products were characterized by mass, thermogravimetric analysis, and Raman and infrared spectroscopy. Conductivity values in the range of 10−10 to 10−5S/cm were determined from ac impedance measurements of the protonated phases below a typical thermal decomposition temperature of about 175C. The decrease in ionic conductivity above the decomposition temperature was consistent with the loss of mobile protons as hydrogen sulfide. Higher proton mobility in the mixed hydrogen alkali thiogermanates vs. the anhydrous thiogermanic acid H4Ge4S10 may be partially attributed to lower decomposition temperatures and increased H bonding.
Anhydrous Proton Conductivity in Hydrogen Alkali Thiogermanates. S.A.Poling, C.R.Nelson, S.W.Martin: Solid State Ionics, 2004, 175[1-4], 581-4