87Rb spin-lattice relaxation times in ferroelectric-paraelectric-incommensurate phases of Rb2CoBr4 using static NMR and MAS NMR

To better elucidate the structural properties of Rb2CoBr4 in paraelectric, incommensurate, and ferroelectric phases, we studied the Rb-87 nuclear magnetic resonance (NMR) spectra and spin -lattice relaxation times in laboratory frame Ti and in rotating frame Ti (rho). The resonance frequency and the chemical shift do not change abruptly near the phase transition temperature of Ti = 333 K and Tc = 192 K, whereas T-1 and T-1 rho display discontinuous changes near T-i and Tc. The abrupt changes in the relaxation times near these temperatures seem to be a result of the structural phase transitions. The results are distinctly different from those reported for Rb2CoCl4. (C) 2017 Elsevier B.V. All rights reserved.