Roles of chemically inequivalent N(CH3)4 ions in phase transition temperatures in [N(CH3)4]2CoCl4 by single-crystal NMR and MAS NMR

The temperature dependences of the H-1 and C-13 spin-lattice relaxation time in the laboratory frame, T-1, and in the rotating frame, T-1 rho, in [N(CH3)(4)](2)CoCl4 were measured by static nuclear magnetic resonance (NMR) and magic angle spinning (MAS) NMR. In the ferroelastic phase, H-1 T-1 rho underwent molecular motion according to the Bloembergen-Purcell-Pound theory. Two inequivalent ions, a-N(CH3)(4) and b-N(CH3)(4), were identified by C-13 cross polarization (CP)/MAS NMR. On the basis of the C-13 NMR results, the existence of two chemically inequivalent a-N(CH3)(4) and b-N(CH3)(4) ions in the ferroelectric phase and the existence of the ferroelastic twin structure of the N(CH3)(4) ions in the ferroelastic phase were discussed. (C) 2014 Elsevier B.V. All rights reserved.