1 research outputs found
Electronic Structure and Electron-Transport Properties of Three Metal Hexacyanoferrates
Metal
hexacyanometallates, or Prussian blue analogs (PBAs), are
active materials in important electrochemical technologies, including
next-generation sodium- and potassium-ion batteries. They have tunable
properties, including reduction potential, ionic conductivity, and
color. However, little is known about their electronic conductivities.
In this work, we use density-functional theory to model the electronic
structure and to explore the likely electron-conduction mechanism
in three promising cathodes (manganese, iron, and cobalt hexacyanoferrate)
in each of three oxidation states. First, we demonstrate that hybrid
functionals reliably reproduce experimentally observed spin configurations
and geometric phase changes. We confirm these materials are semiconductors
or insulators with band gaps ranging from 1.90 eV up to 4.94 eV. We
further identify that for most of the compounds, the electronic band
edges originate from carbon-coordinated iron orbitals, suggesting
that doping at the carbon-coordinated site may strongly affect carrier
conductivity. Finally, we calculate charge-carrier effective masses,
which we find are very heavy. This study is an important foundation
for making electronic conductivity a tunable PBA material property