A polyphosphate composite [NH4PO3]6[(NH4)2SiP4O13] with high ionic conductivity was prepared and characterized by chemical analysis, X-ray diffraction, thermal gravimetry, impedance spectroscopy, and various nuclear magnetic resonance techniques. Experiments were carried out in dry and humid atmospheres at 20 to 300C. During initial heating (activation) of the composite to 300C, a weight loss of 7% due to release of ammonia occurred resulting in a material of the formal composition of [HPO3]3[NH4PO3]3[(NH4)2SiP4O13]. This material was thermally stable between room temperature and 300C. The conductivity was found to be remarkably high (0.1S/cm) in a water-rich environment. Mainly ammonium species could be found in the 1H MAS nuclear magnetic resonance spectra of the non-activated composite, whereas during the activation process another signal due to bridging H increased. Temperature-dependent 2D and 1D exchange nuclear magnetic resonance spectroscopy, pulsed field gradient nuclear magnetic resonance, and stray field gradient nuclear magnetic resonance measurements were performed in order to compare diffusion coefficients and exchange rates with dc conductivities. The small differences between experimentally obtained conductivities and those determined from the measured self-diffusion coefficients by means of the Nernst–Einstein equation hints to an ammonium vehicle as charge carrier, but could be also explained by H+ conductivity. The slow nuclear magnetic resonance exchange rates between hydroxyl groups and ammonium ions exclude proton conductivity via hydroxyl groups.

Polyphosphate Composite - Conductivity and NMR Studies. S.Haufe, D.Prochnow, D.Schneider, O.Geier, D.Freude, U.Stimming: Solid State Ionics, 2005, 176[9-10], 955-63