Phase transition studied by nuclear spin-lattice relaxation in a KHCO3 single crystal

The H-1 and K-39 spin-lattice relaxation times in a KHCO3 single crystal gr own by the slow evaporation method were investigated by employing a NMR spe ctrometer. The relaxation processes of H-1 and K-39 were described by a sin gle exponential function. The large change in the relaxation time at 318 K indicates that the H and K ions are significantly affected during this tran sition. We know that the phase I to phase II transition is a first-order ph ase transition. Experimental results show that the temperature dependences of the spin-lattice relaxation time behavior were quite similar for both nu clei. From these results the activation energies for the H-1 and K-39 nucle i were obtained and the values are similar for both nuclei in phases I and II. The temperature dependences of the spin-lattice relaxation rates of K-3 9 are proportional to T-4 and T-7 with Raman process dominated by the phono n mechanism below T-c and above T-c, respectively.