Figure 1. Reference frames used to describe spin‐lattice relaxation. (Reproduced with permission from [ 12].)

Figure 2. Scheme illustrating different types of characteristic coherence decay times in solid samples.

Figure 3. Example of a basic pulse sequence for measuring spin‐lattice relaxation rates. A series of two‐dimensional – correlation spectra are recorded as a function of a relaxation delay τ. Site‐specific relaxation curves are obtained by following the intensity/volume of cross‐peaks (CP) in the spectra.

Figure 4. Example of a basic pulse sequence for measuring C′ or C ^α spin‐lattice relaxation rates. A series of two‐dimensional – correlation spectra are recorded as a function of a relaxation delay τ. Site‐specific relaxation curves are obtained by following the intensity/volume of cross‐peaks (CP) in the spectra.