The structure of the first lithium-containing bismuth
ortho (o)-thiophosphate was determined using a combination
of powder
X-ray, neutron, and electron diffraction. Li60–3xBi16+x(PS4)36withxin the range of 4.1–6.5
possesses a complex monoclinic structure [space groupC2/c(No. 15)] and a large unit cell with the lattice
parametersa= 15.4866 Å,b= 10.3232 Å,c= 33.8046 Å, and β
= 85.395° for Li44.4Bi21.2(PS4)36, in agreement with the structure as observed by X-ray
and neutron pair distribution function analysis. The disordered distribution
of lithium ions within the interstices of the dense host structure
and the Li ion dynamics and diffusion pathways have been investigated
by solid-state nuclear magnetic resonance (NMR) spectroscopy, pulsed
field gradient NMR diffusion measurements, and bond valence sum calculations.
The total lithium ion conductivities range from 2.6 × 10–7to 2.8 × 10–6S cm–1at 20 °C with activation energies between
0.29 and 0.32 eV, depending on the bismuth content. Despite the highly
disordered nature of lithium ions in Li60–3xBi16+x(PS4)36, the underlying dense host framework appears to limit the dimensionality
of the lithium diffusion pathways and emphasizes once more the necessity
of a close inspection of the structure–property relationships
in solid electrolytes.