  Motivated by a recent proposal by O. P. Sushkov and co-workers to search for
a P,T-violating Schiff moment of the $^{207}$Pb nucleus in a ferroelectric
solid, we have carried out a high-field nuclear magnetic resonance study of the
longitudinal and transverse spin relaxation of the lead nuclei from room
temperature down to 10 K for powder samples of lead titanate (PT), lead
zirconium titanate (PZT), and a PT monocrystal. For all powder samples and
independently of temperature, transverse relaxation times were found to be
$T_2\approx 1.5 $ms, while the longitudinal relaxation times exhibited a
temperature dependence, with $T_1$ of over an hour at the lowest temperatures,
decreasing to $T_1\approx 7 $s at room temperature. At high temperatures, the
observed behavior is consistent with a two-phonon Raman process, while in the
low temperature limit, the relaxation appears to be dominated by a
single-phonon (direct) process involving magnetic impurities. This is the first
study of temperature-dependent nuclear-spin relaxation in PT and PZT
ferroelectrics at such low temperatures. We discuss the implications of the
results for the Schiff-moment search.
