Local environments and dynamics of hydrogen atoms in protonated forms of ion-exchangeable layered perovskites estimated by solid-state 1H NMR

The local environments and dynamics of hydrogen atoms in five samples of protonated forms of ion-exchangeable layered perovskites, Dion-Jacobson-type H[LaNb2O7] and H[LaTa2O7], Ruddlesden-Popper-type H-2[SrTa2O7] and H-2[La2Ti3O10], and H-1.8[(Sr0.8Bi0.2)Ta2O7] derived from an Aurivillius phase, Bi2Sr2Ta2O9, have been investigated by solid-state H-1 nuclear magnetic resonance spectroscopy (NMR). Solid-state H-1 NMR with a magic-angle spinning technique conducted at room temperature reveals that the mean electron densities around the H-1 nuclei in these protonated forms are relatively low, and that they decrease in the following order: H-1.8[(Sr0.8Bi0.2)Ta2O7]> H-2[LaNb2O7]> H-2[SrTa2O7]> H[LaTa2O7]> H-2[La2Ti3O10]. The temperature-dependent solid-state H-1 broad-line NMR spectra measured at 140-400 K reveal a decrease in the signal width for all of these five samples upon heating due to motional narrowing. The NMR spectra of H[LaNb2O7] and H[LaTa2O7] are different from the other three protonated forms due to the weaker dipole-dipole interactions at low temperatures and lower mobility of the hydrogen atoms at high temperatures. (c) 2006 Elsevier Inc. All rights reserved.