Study on the phase transitions by nuclear magnetic resonance of alpha-type RbAl(SO4)2 x 12H2O and beta-type CsAl(SO4)2 x 12H2O single crystals.
The thermodynamic properties, spin-lattice relaxation times, T(1), and spin-spin relaxation times, T(2), of the (27)Al, (87)Rb, and (133)Cs nuclei in MAl(SO(4))(2)x12H(2)O (M=Rb and Cs) crystals were investigated, and the two crystals were found to lose H(2)O with increases in temperature. From our results for T(1) and T(2), we conclude that the discontinuities near T(d) in the T(1) curves of the two crystals correspond to structural changes. In both crystals, below T(d) the water molecules surrounding the Al(3+) and M(+) nuclei form distorted octahedra, whereas above T(d) the water molecules around the Al(3+) and M(+) nuclei form regular octahedra and the environment of the Al(3+) and M(+) nuclei has cubic symmetry. Further, the T(1) for the (27)Al and (87)Rb nuclei in RbAl(SO(4))(2)x12H(2)O below T(d) were found to increase with increasing temperature, whereas the T(1) for the (27)Al and (133)Cs nuclei in CsAl(SO(4))(2)x12H(2)O were found to decrease. It is possible that this difference is due to the different characteristics of alpha- and beta-type crystals.
Ran Lim
Ae
A
Department of Science Education, Jeonju University, Jeonju 560-759, Republic of Korea. aeranlim@hanmail.net