NMR relaxation study of the local environments and phase transitions of CsCr(SO4)2·12H2O and CsAl(SO4)2·12H2O single crystals

✍ Scribed by Ae Ran Lim

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 323 KB
• Volume: 405
• Category: Article
• ISSN: 0921-4526
• DOI: 10.1016/j.physb.2010.01.119

✦ Synopsis

compounds CsCr(SO 4 ) 2 Á 12H 2 O CsAl(SO 4 ) 2 Á 12H 2 O Crystal growth NMR and relaxation Phase transition a b s t r a c t

The physical properties and phase-transition mechanisms of CsCr(SO 4 ) 2 Á 12H 2 O and CsAl(SO 4 ) 2 Á 12H 2 O single crystals were investigated, with the phase transitions of both crystals being determined from DSC and NMR data. The relaxation times of the 27 Al and 133 Cs nuclei in the two crystals undergo significant changes at the temperature lower than the phase transition temperature T C . The variations in the temperature dependence of the spin-lattice relaxation time T 1 near T C are related to the changes in the symmetry of the octahedra of water molecules surrounding Al 3 + and Cs + . The Cs relaxation time in CsCr(SO 4 ) 2 Á 12H 2 O is faster than that in CsAl(SO 4 ) 2 Á 12H 2 O at 300 K; the spin-lattice relaxation time is inversely proportional to the square of the magnetic moment of the paramagnetic ion. From these results, it can be inferred that the different trivalent cation of Cr and Al are responsible for the different spin-lattice relaxation times in the two crystals.