25 research outputs found
Synthesis and Characterization of Amorphous Hydrated Alkali Thio-Hydroxogermanates
The synthesis, structure, and nonhumidified proton conductivity of the hydrated alkali thio-hydroxogermanates, denoted as MxGeSx(OH)4-x·yH2O (1 †x †4, 0 \u3c y \u3c 8) for M = Na, K, Rb, and Cs, are reported. These materials are generally X-ray amorphous when produced by a low-temperature (75 °C) aqueous solution evaporationâprecipitation route. Raman and IR spectroscopies indicate mixed chalcogenide germanium central anions with distinct asymmetric GeâO and symmetric GeâS stretching modes observable around 820â754 and 500â325 cm-1, respectively. These thio-oxoanions possess a combination of thermally stable hydroxyl groups and hydrophilic alkali associated with the nonbridging sulfurs. Alternating current impendence measurements performed under anhydrous conditions on low-pressure sealed pellets reveal fast ionic conductivity, 10-3â10-2 S/cm, for typical temperatures between 100 and 275 °C. The observed falloff in conductivity at higher temperatures is consistent with the appearance of endothermic transitions in differential scanning calorimetry measurements of hermetically sealed samples, presumably from the âboilingâ or sublimation of a crystalline water sublattice. Corresponding onset temperatures were observed between 150 and 275 °C and dependent on the alkali and composition. Under dry atmosphere conditions, thermogravimetric analysis mass loss measurements indicate continuous mass loss above the preparation temperature of 75 °C