C 1 NQR Spin - Lattice Relaxation Mechanism in Ni ( H 2 0 ) 6 SnCl 6 and Mg ( H 2 0 ) 6 SnCl 6 Crystals *
نویسنده
چکیده
The 35C1 NQR spin-lattice relaxation mechanism in isomorphous N i(H 20 ) 6SnCl6 and M g(H20 ) 6SnCl6 crystals is reported. The spin-lattice relaxation time T1(j in the Ni compound is determined mainly by a paramagnetic relaxation. However, above ca. 400 K T1Q decreased rapidly and a log vs. T 1 curve was almost linear. This steep decrease of T1Q was explained by reorientational motions of the anions with an activation energy of 73 kJm ol“ 1. In addition, a double minimum in Tin, which can be interpreted as arising from the fluctuation of the electric field gradient (EFG) at the chlorine site caused by cationic thermal motions, was observed around room temper ature. The temperature dependence of the 35C1 NQ R r iQ in the Mg salt is re-analysed in the light of the EFG-modulation effect caused by a 180° flip motion of the H 20 molecules and an overall reorientational motion of the [Mg(H20 ) 6]2+ octahedral cations as a whole.
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