Nuclear Spin Relaxation of Fluorine in Molten LiBeF₃

Abstract

The spin lattice relaxation time (T₁) of ¹⁹F-nuclear spin in molten LiBeF₃ was measured at frequency of 20 MHz by means of the pulse NMR technique. T₁ becomes a minimum at about 550°C and T₁^-1 can be expressed as τ/(1+ω₂τ₂), where τ is the correlation time and is estimated to be 1.9×10^-15 exp (100×10₃/RT) S. It is suggested that the relaxation mechanism of ₁₉F- in molten LiBeF₃ is due to the dissociation of F ions from [BeF₄] complex ions and the long distance diffusion of F ions in the liquid. At lower temperature the other mechanism prevails, that is, the main contribution to T₁^-1 is the rotation of the complex ions.