Nuclear-spin relaxation of 207Pb in ferroelectric powders

Motivated by a recent proposal by Sushkov and co-workers [Phys. Rev. A 72, 034501 (2005); 73, 022107 (2006)] to search for a P,T-violating Schiff moment of the Pb-207 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, and a PT monocrystal. For all powder samples and independently of temperature, transverse relaxation times were found to be T-2 approximate to 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 approximate to 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. We discuss the implications of the results for the Schiff-moment search.