Nuclear Magnetic Resonance Study of the Crystallographically Inequivalent Cs(I) and Cs(II) in a Cs2CoCl4Single Crystal

133 Cs ( I =7/2) nuclear magnetic resonance in a Cs 2 CoCl 4 single crystal grown by using the slow evaporation method was measured in the two mutually perpendicular crystal planes. The 133 Cs resonances of two different groups, respectively, with two crystallographically inequivalent cesium nuclei, Cs(I) and Cs(II) in the unit cell, were recorded. From their angular dependences, the Cs(I) and the Cs(II) nuclei have different values for the quadrupole coupling constant and the asymmetry parameter. The quadrupole coupling constant and the asymmetry parameter obtained for Cs(I) with a smaller separation were e 2 q Q / h =725 kHz and η=0.58. Those for Cs(II) with a larger separation were e 2 q Q / h =802 kHz and η=0.85. The electric field gradient (EFG) tensors of Cs(I) and Cs(II) are asymmetric, and the orientations of their principal axes do not coincide. The Cs(I) ion surrounded by 11 chlorine ions has a small quadrupole parameter and is high in symmetry. The Cs(II) ion surrounded by 9 chlorine ions has a larger quadrupole parameter and is lower in symmetry than the Cs(I) ion. In addition, the spin–lattice relaxation time for 133 Cs was decreased with increasing temperature in the temperature range from 180 to 400 K. The relaxation behavior of Cs(I) and Cs(II) can be explained by the direct process of scattering from a single phonon.