SPIN-LATTICE RELAXATION TIMES IN DEUTERATED FERROELECTRIC AMMONIUM SULFATE AND FLUOROBERYLLATE

The temperature dependences of the deuteron spin-lattice relaxation times ( T1) in deuterated ammonium sulfate, (ND4) 2SO4, and ammonium fluoroberyllate, (ND4) 2BeF4 have been studied by transient methods over the range 85°-475°K, which includes the ferroelectric transition temperatures for both materials. The temperature dependence of T1 in both salts is interpreted in terms of reorientation of the two nonequivalent ND4+ ions. Within certain temperature regions in both materials, the deuterons in each type of ND4+ ion have a T1 smaller than the spin-diffusion time with the result that they relax independently, making it possible to measure T1 for each group. The activation energy changes little if at all at the phase transition, although there is an abrupt change in T1 for the deuterons in both ND 4+ ions in ammonium sulfate and in one ND4 + ion in ammonium fluoroberyllate. This latter fact has provoked the suggestion that both ammonium ions are involved in the ferroelectric behavior of ammonium sulfate, whereas only one is involved in the fluoroberyllate.