Gradual solid electrolyte transition in (C5H5NH)Ag5I6

Abstract

In specific-heat measurements of the solid electrolyte (${\mathrm{C}}_5$ ${\mathrm{H}}_5$NH)${\mathrm{Ag}}_5$ ${\mathrm{I}}_6$, the disordering of the silver ions shows up in the form of a Schottky-type anomaly. A model calculation of the site occupancies of the ${\mathrm{Ag}}^{+}$ ions and the excess specific heat reproduces the main features of the gradual transition to the solid-electrolyte state in this compound and proves that correlations between ${\mathrm{Ag}}^{+}$ ions play an important role. Single-crystal conductivity measurements were carried out both along and perpendicular to the hexagonal axis. The large anisotropy of the conductivity at low temperatures ascertains that the motion of the ${\mathrm{Ag}}^{+}$ ions through the channels provided by the $c$ sites is much easier than the motion via pathways involving $m$ sites. In addition, the specific-heat measurements show the existence of a second-order phase transition which is probably associated with the orientational disordering of the pyridinium ions. Finally, single-crystal conductivity results of ${\left({\mathrm{C}}_5{\mathrm{H}}_5\mathrm{N}\mathrm{H}\right)}_5$ ${\mathrm{Ag}}_{18}$ ${\mathrm{I}}_{23}$ are presented which confirm the prediction of Geller et al. that this material is a two-dimensional solid electrolyte.