Electrical conductivities of the Ag6PS5X and the Cu6PSe5X (X=Br, I) argyrodites

The Ag6PS5Br and Ag6PS5I argyrodites crystallize in a face-centered-cubic lattice at room temperature. Both compounds exhibit purely Arrhenius behavior throughout the temperature range 150-400 K with similar activation energies of about 0.23 eV. Cu6PSe5Br and Cu6PSe5I also crystallize in a face-centered-cubic structure at room temperature. Cu6PSe5Br exhibits a distinctive anomaly in electrical conductivity near 286 K while Cu6PSe5I undergoes a first-order electrical phase transition near 265 K. Their activation energies above room temperature are 0.13 and 0.30 eV, respectively.