Heat capacity and N. M. R. study of the NH4MgF3perovskite

Abstract
The NH4MgF3 perovskite undergoes a structural and reorientational phase transition at Tc=107. 5±0. 1 K. The librational motion of the NH+ 4 ion below Tc is hindered by a barrier producing an activation energy of Ea/k = 850 K, and correlation time of c=50 fs, as found in N. M. R. measurements. Tunnelling in the ground state multiplet is detected as well.