Figure 1

Time-dependent $\mu \mathrm{\text{−}}e$ decay asymmetry ($\propto$ muon polarization) observed in undoped (a),(b) and Ti-doped (c),(d) ${\mathrm{NaAlH}}_4$, respectively, at about 5 and 240 K under zero external field. The full polarization corresponds to $\sim 0.18$ for  (a),(b) (PSI data), and $\sim 0.26$ for (c),(d) (TRIUMF data). Solid curves are those obtained by fitting analysis using the model described in the text, where contributions of $G_{3\mathrm{S}}(t)$ and $G_{\mathrm{KT}}(t)$ are displayed by broken curves.Reuse & Permissions

Figure 2

Temperature dependence of (a) ${\omega }_d$, (b) $\Lambda$, (c) $\Delta$, (d) $\nu$, and (e) $f_d$ extracted from $\mu \mathrm{SR}$ spectra using ${\chi }^2$-minimization fits. The value of reduced ${\chi }^2$ is also shown in (f). For the fractional yields ($f$ and $g$), see Fig. 3.Reuse & Permissions

Figure 3

Temperature dependence of the fractional yield for (a) muon-dialanate state ($f$), (b) muons at the O site ($g$), and (c) undamped state ($h$), where $f+g+h\equiv 1$. Solid curves represent the best fit to a simple activation model shown in the text. (d) Crystal structure of ${\mathrm{NaAlH}}_4$ where half of the unit cell is displayed. Dark gray (blue) (Al) and light gray (pink) (Na) atoms occupy the vertices of a fcc lattice, and tetrahedra represent the alanate ions (${\mathrm{AlH}}_4^{-}$) in which the corners are occupied by H (those at the bottom are not shown for clarity). Possible muon (and H) sites are marked by the diamond (labeled C, forming a collinear ${\mathrm{AlH}}_4^{-}\mathrm{\text{−}}{\mu }^{+}\mathrm{\text{−}}{\mathrm{AlH}}_4^{-}$ hydrogen bond) and by the square (labeled O, an octahedral interstitial site).Reuse & Permissions