Alignment echo

Fig. 6. The generalized Jeener-Broekaert three pulse sequence. Note that FT of the solid echo and the alignment echo starts at times delayed by the pulse separation r, after the second and third pulse, respectively...

Fig. 11a and b. Decay of the alignment echo height as a function of the mixing time x2 for different motional mechanisms, a Tetrahedral jumps as a model for conformational changes b Diffusive motion, the solid lines correspond to unrestricted rotational diffusion, the dashed lines to diffusion restricted to an angular region of 8°. Note the strong dependence of the decay curves on the evolution time t, in case of diffusive motion... 

Fig. 18.2H FT spectra of the alignment echo for different waiting times t2 and different temperatures. Sample LPE, amorphous fraction...

Be NMR has been used to detect slow atomic motion of beryllium in Zr-Ti-Cu-Ni-Be metallic glasses. The results, obtained by a spin alignment echo technique, are consistent with Be diffusion occuring by a mechanism involving thermal fluctuations of the spread-out free volume rather than by vacancy-assisted or interstitial diffusion mechanisms (Tang et al. 1998). 

To bypass receiver deadtime effects, wideline spectra are derived by Fourier transformation of the decay of an echo. By use of the Hahn echo and the stimulated echo (Section 2.2.1), wideline spectra of and other spin-5 nuclei can be measured, for example, but not the spectra of dipolar coupled spins and of quadrupolar nuclei like H. The magnetization of nuclei with spin / = 1 can be refocused by the quadrupole echo or the solid echo, and by the Jeener-Broekaert echo or the alignment echo [Slil] (Fig. 3.2.6). 

A detailed quantitative analysis of timescale and angle distribution requires numerical simulation of the spectra acquired with the solid and the alignment echoes. To this end the time-domain signal is written as a vector. The components of which correspond to the different molecular orientations [Abrl, Andl],... 

Many NMR techniques rely on the formation of magnetization echoes [Bagl, Blu5]. Examples are (1) the measurement of T2 relaxation times by the Hahn echo (Section 2.2), (2) the analysis of slow motion by stimulated echoes for spins with / = 1/2, and for nuclei with spin / = 1 or pairs of coupled spins with / = 1/2 by the solid echo and the alignment echo (Section 3.2), (3) MAS, where echoes are generated by mechanical... 

Figure 8.2 Basic 1-D pulse sequences (a) the quadrupole echo (b) the spin-alignment echo (c) inversion-recovery quadrupole echo and (d) quadrupole echo with pre-saturation for amorphous/crystalline selection, t is the quadrupole echo pulse spacing in each sequence, DE is a delay for spin-lattice relaxation, of either (b) quadrupolar order or (c) and (d) Zeeman order. Flip angles are labelled above the pulses.

The three-pulse spin-alignment echo [111,112] (90y-T-45 -DE-45-T-echo, Figure 8.2(b)) provides a second method with which to obtain a spectrum. For DE = 0, the experiment is similar to a quadrupole echo and the DE dependence is determined by slow reorientation (10" < < lO s). In the... 

The stndy of Li-ion conductors is driven by the ambitions effort to design powerful hthium-ion batteries. Li as well as Li spin-alignment echo (SAE NMR) spectroscopy, which is capable of probing long-range diffnsion parameters from a microscopic, that is, atomic-scale, point of view was... 

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