Ferroelectric mode in ammonium sulfate

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Abstract
Proton spin–lattice (T1), rotating frame (T1ρ), and dipolar (T1D) relaxation times are reported in (NH4)2SO4 from 200 to 300 °K. At 236 °K T1ρ is measurably shorter than T1 and T1D? (1/3) T1. These results are in agreement with the results recently reported by Knispel et al. T1 is dependent on frequency at 298 °K in the range 13 to 60 MHz. These effects are interpreted in terms of a ’’ferroelectric mode’’ process that was proposed earlier, and flip times τf are computed that are associated with the two angles of tilt of the distorted NH4+ tetrahedra from the ab mirror plane in the paraelectric phase. At 298 °K, τf=6.7×10−9 sec.