Nuclear magnetic resonance study of anion and cation dynamics in CsSiH3

Abstract In order to study the dynamical properties of cesium silanide CsSiH 3 , we have measured the 1 H and 133 Cs nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates in this compound over the temperature range of 5–354 K. The results of the 1 H NMR measurements indicate that [SiH 3 ] ‒ anions in CsSiH 3 retain unusually high reorientational mobility down to low temperatures. In particular, a significant narrowing of the proton NMR spectrum due to [SiH 3 ] ‒ reorientations is observed in the range ∼ 10–14 K. The order-disorder (β→α) phase transition accompanied by the strong acceleration of [SiH 3 ] ‒ reorientations and by the change in the reorientational mechanism is observed above 200 K; according to the 1 H spin-lattice relaxation data, this transition appears to be gradual. For the high-temperature disordered α-phase, the activation energy for [SiH 3 ] ‒ reorientations is found to be 41(4) meV. The 133 Cs NMR results are consistent with the onset of diffusive motion of Cs + cations at the frequency scale of ∼10 4 s −1 above 300 K.