Nuclear magnetic resonance linewidth studies were made of polycrystalline samples at temperatures ranging from -50 to 190C. Line-narrowing was observed above -10C. The results could be described by:

D (cm2/s) = 2.5 x 10-6 exp[-0.35(eV)/kT]

Diffusion proceeded via a vacancy mechanism.

Motional Narrowing of 19F Nuclear Magnetic Resonance in Lead Fluoride. M.Mahajan, B.D.N.Rao: Chemical Physics Letters, 1971, 10[1], 29-30