This
research demonstrates the cation and anion transfer of an
organic ionic plastic crystal (OIPC), quinuclidinium hexafluorophosphate
([HQ]PF6), in the pure state and mixtures doped with lithium
or chloride ions. The pure material and the mixtures show relatively
simple thermal behaviors. Powder X-ray diffraction determined a cubic
crystal structure, a common feature of OIPCs, in the high-temperature
phase of the pure material. Solid-state nuclear resonance spectra
of the pure material reveal rotation-assisted ion mobility and the
presence of the plastic crystal phase. The ionic conductivity of the
mixtures doped with lithium ions and chloride ions increases significantly.
Arrhenius conduction behaviors are observed in both the pure material
and ion-doped mixtures, with effective activation energies of ∼60–110
kJ mol–1. Ionic conductivity also implies that ions
transfer either through the bulk crystal or via grain boundaries.
This is the first time that the cation and anion transfer in a quinuclidinium-based
OIPC is reported, and the anion (here Cl–) is transferred
in plastic crystal systems where solid solutions are likely formed.
Different ion conduction behaviors of the pure and doped materials
are closely associated with shapes and relative sizes of constituent
ions. The results provide useful information to improve the understanding
of structure–property relationships in OIPCs.