Effect of cationic substitution on the double-well hydrogen-bond potential in [K_1−x (NH₄) _x ]₃H(SO₄)₂ proton conductors: a single-crystal neutron diffraction study

Abstract

The structure of the mixed crystal [K(NH)]H(SO) as obtained from single-crystal neutron diffraction is compared with the previously reported room-temperature neutron structure of crystalline KH(SO). The two structures are very similar, as indicated by the high value of their isostructurality index (94.8%). It was found that the replacement of even a small amount (3%) of K with NH has a significant influence on the short strong hydrogen bond connecting the two SO ions. Earlier optical measurements had revealed that the kinetics of the superionic transition in the solid solution [K(NH)]H(SO) are much faster than in KH(SO); this reported difference in the kinetics of the superionic phase transition in this class of crystal is explained on the basis of the difference in strength of the hydrogen-bond interactions in the two structures.

Implementation of Phase Transitions in Rb3H(SO4)2 under K Substitution

“…The introduction of about 5% at. ammonium into K 3 H(SO 4 ) 2 leads to an elongation of hydrogen bonds (d O-O = 2.496(1) Å → 2.549(8) Å) and anomalously slow kinetics of the phase transition becomes typical for superprotonic transitions [27]. The introduction of 57% at.…”