Phase Transition Studied by Nuclear Spin–Lattice Relaxation in a KHCO ₃ Single Crystal

Abstract

The 1 H and 39 K spin-lattice relaxation times in a KHCO 3 single crystal grown by the slow evaporation method were investigated by employing a NMR spectrometer. The relaxation processes of 1 H and 39 K were described by a single exponential function. The large change in the relaxation time at 318 K indicates that the H and K ions are significantly affected during this transition. We know that the phase I to phase II transition is a first-order phase transition. Experimental results show that the temperature dependences of the spin-lattice relaxation time behavior were quite similar for both nuclei. From these results the activation energies for the 1 H and 39 K nuclei 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 39 K are proportional to T 4 and T 7 with Raman process dominated by the phonon mechanism below T c and above T c , respectively.

NMR study of the order–disorder phase transitions of KHCO3 and KDCO3 single crystals

“…The changes in the relaxation time near T C ( ¼ 318 K) indicates that the 1 H and 39 K ions were significantly affected during this transition. And, the 39 K spin-lattice relaxation time was in accordance with the Raman process below and above T C [19]. Recently, Odin [20] investigated the phase transition of powder KHCO 3 by the 13 C and 39 K high-resolution solid-state NMR.…”

“…The changes in the T 1 curves near 318 K correspond to the first-order phase transition. The spin-lattice relaxation time T 1 of 1 H in KHCO 3 was found to be long: 517 s at 230 K and 141 s at 350 K. The relaxation times of 39 K were found to be short: 2.40 s at 220 K and 0.32 s at 350 K. In both cases, the relaxation time was found to decrease with increases in temperature below T C , whereas it increased with increases in temperature above T C [19]. The relaxation time of 1 H was found to be longer than that of 39 K.…”

A neutron diffraction study of macroscopically entangled proton states in the high temperature phase of the KHCO3crystal at 340 K

“…Kashida and Yamamoto [9] have opposed the ordered C 2h to the disordered C i structures. The argument consists in that for the former there is no splitting of heavy atom sites and the symmetrized double wells for protons lead to quantum delocalization [6,14,16,17,47]. By contrast, split C i dimers are supposed to be representative of a statistical distribution of atom positions and the double well remains asymmetric, as it is below T c .…”

“…The population ratio R:L increases discontinuously to 0.5:0.5 and then remains a constant above T c . This transition, supposed to be of the order-disorder type [9][10][11][12][13][14][15][16][17], could be of great significance to experimental studies of the quantum-to-classical interface in the crystalline state. However, structural and dynamical models are still in debate and require further studies.…”

13C and 39K High-Resolution Solid-State NMR Study of the Nonferroic Phase Transition of Potassium Hydrogen Carbonate. Complementarity between NMR and Incoherent Neutron Scattering

“…To our knowledge, only one article refers explicitly to the nonferroic phase transition, namely to explain the proton spinlattice relaxation behavior as a function of temperature. 28 The other articles did not consider the phase transition because its existence was not known at that time (the monoclinic/monoclinic phase transition was discovered by Haussu ¨hl in 1986). The proton chemical shift tensor was measured at ambient temperature.…”