Nature of the Ferroelectric Transition in Triglycine Sulfate

The occurrence of linewidth transitions in the proton magnetic resonance spectra of triglycine sulfate, selenate, and fluoberyllate at the corresponding Curie points demonstrates that the ferroelectric transitions in these crystals are connected with a rearrangement of the basic ionic units in the unit cell. The results of a combined proton magnetic and infrared study confirm the crystal structure proposed by Pepinsky and co-workers. Further they show that the ferroelectric transition in triclycine sulfate and its isomorphs is of the order-disorder type and basically of the same nature as that in K${\mathrm{H}}_2$P${\mathrm{O}}_4$. The chief difference is the strong coupling of the protonic motion in triglycine sulfate with the motions of heavier groups.