Ultraslow Hydrogen Motion in KH2PO4 and NaH3(SeO3)2 Type Crystals

Abstract

Ultraslow reorientational motions of the H2PO4 and H2SeO3 groups have been studied in KH2PO4, RbH2PO4, CsH2PO4, LiH3(SeO3)2, NaH3(SeO3)2, KH3(SeO3)2, and CsH3(SeO3)2 by dipolar and rotating frame proton spin–lattice relaxation measurements. The measured values of the reorientational correlation times change from about 10−3 sec at room temperature to about 10−5 sec at 100°C. The activation energies for the hindered rotation of the H2PO4, respectively, H2SeO3 groups are controlled by the size of the cation rather than by the strength of the O–H···O bonds, and vary from 0.4 to 1.4 eV. In contrast to the case of ice this slow reorientational process dominates the dc protonic conductivity of both the KH2PO4 and the NaH3(SeO3)2 group of hydrogen bonded crystals.

Superprotonic phase transition ofCsHSO4: A molecular dynamics simulation study

“…A similar type of threefold rotation was proposed to explain the results of H + NMR studies on KH 2 PO 4 . 42,43 This behavior may well be a general phenomenon in solid acid proton conductors in their nonsuperprotonic phases, and the gradual rise in the frequency of the reorientations may explain the gradual increase in conductivity typically observed as a solid acid compound is heated to its superprotonic transition. For further discussion of force field parameters affecting these reorientation and rotation rates see Sec.…”

Proton migration in solids

“…Independently Blinc and Pirg found by means of N.M.R. that slow rotation of H2PO 4 dominates the conduction process [38]. With a known amount of dopant it is possible to calculate the mobility of an L defect: PL = 6X 10 -1° cm 2 V -1 s -1.…”

“…In connection with electrolysis experiments a good indication is obtained that the deuteron is indeed the mobile species in KD2PO4. Continued rotating frame and dipolar proton spin-lattice relaxation measurements reveal that a slow reorientational process dominates the d.c. protonic conductivity in KH2PO4 [38].…”

Study of the ferroelectric–paraelectric phase transition of NaH3(SeO3)2 single crystals by 1H and 23Na NMR

“…The quadrupole coupling constant, the asymmetry parameter, and the direction of the principal axes of the electric field gradient (EFG) tensors of 2 D and 23 Na in NaD 3 (SeO 3 ) 2 were obtained by Soda and Chiba [8]. Further, the proton relaxation time in the rotating frame for powder samples was dominated by the slow reorientational process of the SeO 3 groups [9]. Although the quadrupole parameters for NaH 3 (SeO 3 ) 2 and NaD 3 (SeO 3 ) 2 have been reported, the 1 H and 23 Na spin-lattice relaxation times in the laboratory frame for NaH 3 (SeO 3 ) 2 single crystals have not yet been studied.…”