Korringa spin lattice relaxation temperature independence

The temperature independence of the Korringa product T T is a better indicator of the metallic character of an NMR signal than the value of its shift. In most metal hydrides, the spin lattice relaxation at room temperature contains important contributions from the diffusive motion of the proton in the hydride lattice. To investigate the Korringa product one must work at relatively low temperatures for the palladium hydrides only values of x > 0.65 are accessible (Fig. 20). For x = 1, 7 T = 46 sK (67), but no values have been given for the shift. Supposing that the total shift 5(1) can be derived from Eq. (21) with the parameters given previously for the palladium black, we obtain 5(1) 51 ppm. From the Ti T value... 

Fk . 22. Spin lattice relaxation rate Tl of II in bulk Pdll, with x in the 0.7 to 0.8 range as a function of temperature and for several Larmor frequencies vo The straight line indicates a temperature-independent Korringa product TiT. characteristic of metallic behavior there is a nonzero LDOS on the H at the Fermi energy, in qualitative agreement with Fig. 21b. [Reproduced with permission from Schoep el al (68). Copyright 1974 Filsevier Science.]... 

Fig. 45. Time/temperature scaling of spin lattice relaxation curves in a saturation-recovery experiment. At each temperature the raw amplitude data arc first normalized by the amplitude of the fully relaxed signal so that all values fall between zero (saturation at short times) and 1 (lull recovery at long times). The time points t are multiplied by the temperature at which the relaxation curve was obtained. If the relaxation is governed by the Korringa process, the scaled points fall on a temperature-independent curve, even if the relaxation is not simply exponential, as in the cases shown here. The sample is Pt/Ti02 of dispersion 0.60 (determined by electron microscopy) at several hydrogen coverages (calculated from the dispersion) 0.1, 0.5, and 1.0 monolayers. The squares in c show data at 110 K for another Pt/TiOi catalyst of dispersion 0.36.

---