Variable temperature Pb-207 NMR of PbTiO3

A variable temperature Pb-207 solid-state NMR study of lead titanate was co nducted between -150 and 60 degrees C. The isotropic lead chemical shift is only weakly dependent on temperature, probably because of changes in: the average Pb-O distance, which is known to be correlated with the chemical sh ift. In contrast, the chemical shielding anisotropy increases markedly with lower temperature, and an excellent correlation is observed between the ma gnitude of the shielding,anisotropy and the square of the tetragonal distor tion parameter c/a - 1. The chemical shift powder pattern remains axially s ymmetric over the entire temperature range, ruling out any substantial lowe ring of symmetry; it is unlikely, however, that the very small orthorhombic distortions detected in recent powder X-ray work can be observed by NMR. ( C) 2000 Elsevier Science Ltd. All rights reserved.