Spin-Lattice Relaxation Time of Proton in (NH4)2SO4–K2SO4 Mixed Crystals

The temperature dependence of the proton spin-lattice relaxation time T 1 of [(NH 4 ) 1- x K x ] 2 SO 4 was studied. As the concentration of K 2 SO 4 , x increases, it is found that (1) the temperatures of two T 1 minima shift downwards, (2) T 1 versus 1/ T curves become broader near each T 1 minimum and (3) T 1 at the right minimum is longer than that at the left minimum for x ≤0.19. The experimental result (3) may suggest that more K + ions are substituted for NH 4 + (I) than for NH 4 + (II) ions. A single T 1 minimum curve is obtained for x =0.84. This means that only one type of NH 4 + ions, NH 4 + (II), remains at higher concentration of K 2 SO 4 .