Cation Transport in Li$^+$ and Na$^+$ Rich Antiperovskites

A large number of compounds possessing the perovskite crystal structure demonstrate interesting properties such as ferroelectricity, magnetoresistance, and superconductivity. In this study, we present findings on a new class of materials, namely Li$^+$ and Na$^+$ rich antiperovskites, with emphasis on cation transport for solid state battery applications. The electrolytes have the general formula $A_3BX$ where A is a Li$^+$ or Na$^+$ cation, B is an O$^{2-}$ or S$^{2-}$ anion, and X is a Cl$^-$ or Br$^-$ anion; mixed compositions were also studied. X-ray diffraction techniques were used for phase identification, sample purity, and unit cell refinement. In each case, the materials crystallize in a cubic unit cell with space group $Pm\bar{3}m$. The ionic conductivity was determined for each material as a function of temperature using impedance spectroscopy methods. Activation energies for cation diffusion were determined by fitting the conductivity data to the Arrhenius equation $\sigma = \frac{\sigma_0}{T}e^{-E_a/k_BT}$.