27Al Magic Angle Spinning Nuclear Magnetic Resonance Study of Al1−x Cr x K(SO4)2·12H2O (x = 0, 0.07, and 0.2)

Behavior of H2O surrounding NH4+and Al3+in NH4Al(SO4)2·12H2O by1H MAS NMR,14N NMR, and27Al NMR

“…According to the crystallography results previously reported, the NH 4 tetrahedron appears to be slightly elongated along a 3-fold symmetry axis; the NH 4 + ions have a longer N-H distance and shorter N-H distance. 25 The results of the three groups of 14 N show that the tetrahedral symmetry for NH 4 + ion is not highly symmetric and that the stronger distortion of the crystallography is indicated. In addition, this splitting of the 14 N Fig.…”

“…The magnetic eld was applied along the crystallographic axis. The in situ 14 N NMR spectra and the resonance frequency in NH 4 Al(SO 4 ) 2 $12H 2 O single crystals are plotted in Fig. 5(a and b), as a function of temperature.…”

“…A complex network of H-bonds is one of the main features of alum structures. Current interest in these compounds lies in the fact that a number of them, particularly when A I is NH 4 , are ferroelectric at low temperature. H MAS NMR spectra and the spin-lattice relaxation time T 1r in the rotating frame were obtained at the Larmor frequency of 400.13 MHz using a Bruker 400 MHz NMR spectrometer at the Korea Basic Science Institute, Western Seoul Center.…”

“…1 H T 1r values were determined using a p/2-t sequence by varying the duration of the spin-locking pulses. The widths of the p/2 pulses used for measuring the T 1r values of 1 H were 3.6 ms below 340 K and 4.35 ms above 350 K. In addition, the 14 N NMR spectra of the NH 4 Al(SO 4 ) 2 $12H 2 O single crystals in the laboratory frame were measured using a Unity INOVA 600 NMR spectrometer at the Korea Basic Science Institute, Western Seoul Center. The static magnetic eld was 14.1 T, and the Larmor frequency was set to u 0 /2p ¼ 43.342 MHz.…”

“…The alums can be represented by the general formula A I B III (SO 4 ) 2 $12H 2 O, where A is a monovalent cation such as Na, K, Rb, Cs, or NH 4 , and B is a trivalent cation such as Al, Fe, or Cr. [1][2][3][4][5][6][7][8][9][10][11] It is well known that there are a considerable number of alums A I B III (SO 4 ) 2 $12H 2 O that exhibit ferroelectric activity.…”