title: Solid-state NMR study on changes of phosphate and proton species in metal pyrophosphate composite (MP2O7-MO2) ceramics.
abstract: 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 (MP2O7-MO2; M = Sn, Si, Ti, and Zr). Acidic species could be detected by1H MAS NMR spectra for all the composites except ZrP2O7-ZrO2that had the lowest conductivity. The31P DD-MAS NMR spectra for MP2O7-MO2composites showed different signal patterns depending on the counter cations participating in the ion exchange as a result of different microstructures. Combinational analysis of31P DD-MAS and31P 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 MP2O7-MO2composites. After water washing, the acidic species and the protonic bulk phosphates of MP2O7-MO2composites disappeared or were reduced to trace amounts. The T1H values of the water-washed composites lengthened because of removal of orthophosphoric acid, although the T1P values remained almost unchanged. The results of the solid-state NMR studies suggest that the protonic bulk phosphates of MP2O7-MO2composites do not generally distribute in the bulk but exist in the interface between excess H3PO4and the bulk. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Moriyama-ku, Nagoya, Japan.
authors.forename: Masakazu
authors.identifier: http://orcid.org/0000-0001-6588-9566
authors.initials: M
authors.lastname: Nishida
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Moriyama-ku, Nagoya, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Tanaka
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Moriyama-ku, Nagoya, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Kanematsu
keywords: 1H; 29Si; 31P; NMR; composite ceramics; counter cation effect; cross polarization; proton conductor; relaxation time analysis