Cation Diffusion Study in NH4NO3 by Proton Spin Relaxation

Abstract

Measurements of the proton spin—lattice relaxation times (T1, T1ρ) have been made to study the translational and reorientational motions of the ammonium ions in ammonium nitrate in several solid phases. At the plastic-to-brittle phase transition at 398°K, the correlation time for translational diffusion of the NH4+ ion increases by more than three orders of magnitude: the increase is from 2 × 10−14exp(12.1 kcal mole−1 / RT) to 2 × 10−16exp (24.3 kcal mole−1/RT) sec. The self-diffusion constants for NH4+ in phases II and I obtained from these correlation times are in close agreement with the diffusion constants reported from electrical conductivity measurements in phases II and I.