New solid electrolyte: CsCu4Cl3I2

Abstract

The solid electrolyte $\ensuremath{\alpha}$-Cs${\mathrm{Cu}}_{4}$${\mathrm{Cl}}_{3}$${\mathrm{I}}_{2}$ is thermodynamically stable above 431 K and to at least 505 K. It is isostructural with Rb${\mathrm{Cu}}_{4}$${\mathrm{Cl}}_{3}$${\mathrm{I}}_{2}$. At 431 K it has a conductivity of $0.76{\ensuremath{\Omega}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, at 419 K the conductivity is $0.72{\ensuremath{\Omega}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ and extrapolation to 298 K gives $0.29{\ensuremath{\Omega}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. When corrected for deviation of bulk from x-ray density, the expected values are 0.84, 0.80, and $0.35{\ensuremath{\Omega}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively. Its activation enthalpy of motion is 0.112 eV. There are two first-order phase transitions: $\ensuremath{\beta}\ensuremath{-}\ensuremath{\alpha}$ at 431 K and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\beta}$ at 418 K; both are very sluggish. The $\ensuremath{\alpha}$ phase does not reconvert to the $\ensuremath{\beta}$ phase; it returns to the $\ensuremath{\gamma}$ phase below \ensuremath{\sim}418 K. At 298 K the conductivity of the $\ensuremath{\gamma}$ phase is $5.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, at 425.5 K, the conductivity of the $\ensuremath{\beta}$ phase is $0.11{\ensuremath{\Omega}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. The enthalpy of activation of motion of the $\ensuremath{\beta}$ phase is 0.77 eV. The $\ensuremath{\gamma}$ phase is orthorhombic with $a=14.242$, $b=24.984$, $c=11.712$ \AA{}, probable space groups $\mathrm{Cmca}$ or $C2\mathrm{ca}$, and 16 Cs${\mathrm{Cu}}_{4}$${\mathrm{Cl}}_{3}$${\mathrm{I}}_{2}$ in the unit cell.