Solid-state NMR study on changes of phosphate and proton species in metal pyrophosphate composite (MP O -MO ) ceramics.

In order to investigate the effects of composite production and the role of the counter cation for metal phosphate conductors, changes in the solid-state nuclear magnetic resonance (NMR) spectra and magnetic relaxation times caused by the removal of volatile products and water washing were examined for various metal pyrophosphate (MP O -MO ; M = Sn, Si, Ti, and Zr). Acidic species could be detected by H MAS NMR spectra for all the composites except ZrP O -ZrO that had the lowest conductivity. The P DD-MAS NMR spectra for MP O -MO composites showed different signal patterns depending on the counter cations participating in the ion exchange as a result of different microstructures. Combinational analysis of P DD-MAS and P CP-MAS NMR spectra of the composites indicated that protonic bulk phosphates were observed at slightly lower fields than non-protonic bulk phosphates in all of the MP O -MO composites. After water washing, the acidic species and the protonic bulk phosphates of MP O -MO composites disappeared or were reduced to trace amounts. The T H values of the water-washed composites lengthened because of removal of orthophosphoric acid, although the T P values remained almost unchanged. The results of the solid-state NMR studies suggest that the protonic bulk phosphates of MP O -MO composites do not generally distribute in the bulk but exist in the interface between excess H PO and the bulk. Copyright © 2016 John Wiley & Sons, Ltd.