Order-disorder and ionic conductivity in calcium nitride-hydride

Gavin John Irvine*, Ronald I Smith, Martin Owen Jones, John Thomas Sirr Irvine*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

Recently nitrogen-hydrogen compounds have successfully been applied as co-catalysts for mild conditions ammonia synthesis. Ca2NH was shown to act as a H2 sink during reaction, with H atoms from its lattice being incorporated into the NH3(g) product. Thus the ionic transport and diffusion properties of the N–H co-catalyst are fundamentally important to understanding and developing such syntheses. Here we show hydride ion conduction in these materials. Two distinct calcium nitride-hydride Ca2NH phases, prepared via different synthetic paths are found to show dramatically different properties. One phase (β) shows fast hydride ionic conduction properties (0.08 S/cm at 600 °C), on a par with the best binary ionic hydrides and 10 times higher than CaH2, whilst the other (α) is 100 times less conductive. An in situ combined analysis techniques reveals that the effective β-phase conducts ions via a vacancy-mediated phenomenon in which the charge carrier concentration is dependent on the ion concentration in the secondary site and by extension the vacancy concentration in the main site.
Original languageEnglish
Article number4389
Number of pages8
JournalNature Communications
Volume14
DOIs
Publication statusPublished - 20 Jul 2023

Keywords

  • Hydride ion conductor
  • Ammonia synthesis
  • Combined analysis
  • Nitride-hydride

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