PDF Study of Dynamic Correlated Disorder in the Hydride Ion Conductor Ca2NH

Calcium nitride-hydride (Ca2NH) has been shown to promote mild-condition ammonia synthesis as a co-catalyst (Kitano et al., Chem. Sc., 2016). Kitano et al. suggested Ca2NH acted as a hydrogen sink freeing up active sites on the transition metal (Ru) for further disassociation of N2 and H2 gases. EIS conducted at the University of St Andrews shows temperature dependent conductivities associated with type-II (thermally induced) ionic conductors (Boyce, Physics Reports, 1979). A previous QENS experiment (RB 1720393) showed significant Q-dependent broadening associated with this system, strongly indicating H- diffusion. Thus, it’s likely that the ionic conductivity of systems like Ca2NH play a significant role in promoting ammonia synthesis. A PDF experiment could explore the nature of this ionic conductivity and its relation to the structure of Ca2NH. Recent research has pin-pointed correlated disorder as a potential source for high ionic conductivities measured in solid-state systems (Keen & Goodwin, Nature, 2015). Analysis of our previous PDF experiment (RB 1610383) will soon be published in a Chemistry of Materials article outlining the relationship between correlated disorder and ionic conductivity in the superionic conductor BaH2. A clear understanding of the relationship between structure, correlated disorder, and ionic conductivity in the Ca2NH system will benefit future research into nitrogen-hydrogen based co-catalysts for mild-condition ammonia synthesis.