Temperature variation of the molecular structure of lithium hydrazinium sulphate—a one-dimensional proton conductor

The paper reports the results of detailed studies of the molecular structure of lithium hydrazinium sulphate single crystal in a wide temperature range with the aim to clarify previously reported anomalies in the molecular dynamics at ,100 K. The crystal does not undergo any structural phase transition from 8 to 460 K however, the donor-acceptor distance, between the nitrogen atoms involved in the hydrogen bond along the c-orthorhombic axis, starts to increase from the temperature of ,100 K. This results in an anomaly of the phase memory time observed in electron spin echo studies and anomalies of hydrazinium internal modes observed in Raman scattering. Moreover, the anisotropy of the SO4 tetrahedra is maximal at ,100 K and decreases at higher temperatures. The possible contribution of fast proton transport, described by the Grotthuss model, to the proton conductivity along the c-axis at the temperature above ,400 K is discussed. q 2003 Elsevier B.V. All rights reserved.