Order-disorder and ionic conductivity in calcium nitride-hydride.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 37474517.
- Also identified by DOI 10.1038/s41467-023-40025-2 and PMC identifier 10359262.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Recently nitrogen-hydrogen compounds have successfully been applied as co-catalysts for mild conditions ammonia synthesis. Ca<sub>2</sub>NH was shown to act as a H<sub>2</sub> sink during reaction, with H atoms from its lattice being incorporated into the NH<sub>3</sub>(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 Ca<sub>2</sub>NH 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 CaH<sub>2</sub>, 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.