Anhydrous Silicophosphoric Acid Glass: Thermal Properties and Proton Conductivity

Anhydrous silicophosphoric acid glass with an approximate composition of H5Si2P9O29 was synthesized and its thermal and proton-conducting properties were characterized. Despite exhibiting a glass transition at 192 degrees C, the supercooled liquid could be handled as a solid up to 280 degrees C owing to its high viscosity. The glass and its melt exhibited proton conduction with a proton transport number of similar to 1. Although covalent O-H bonds were weakened by relatively strong hydrogen bonding, the proton conductivity (4x10(-4) S cm(-1) at 276 degrees C) was considerably lower than that of phosphoric acid. The high viscosity of the melt was due to the tight cross-linking of phosphate ion chains by six-fold-coordinated Si atoms. The low proton conductivity was attributed to the trapping of positively charged proton carriers around anionic SiO6 units (expressed as (SiO6/2)(2-)) to compensate for the negative charges.

Automated summary

Anhydrous silicophosphoric acid glass exhibited high viscosity at high temperatures, displayed proton conduction, but had lower conductivity.