New solid electrolyte: CsCu₄Cl₃I₂

Abstract

The solid electrolyte α-CsCu₄Cl₃I₂ is thermodynamically stable above 431 K and to at least 505 K. It is isostructural with RbCu₄Cl₃I₂. At 431 K it has a conductivity of 0.76Ω^-1 cm^-1, at 419 K the conductivity is 0.72Ω^-1 cm^-1 and extrapolation to 298 K gives 0.29Ω^-1 cm^-1. When corrected for deviation of bulk from x-ray density, the expected values are 0.84, 0.80, and 0.35Ω^-1 cm^-1, respectively. Its activation enthalpy of motion is 0.112 eV. There are two first-order phase transitions: β-α at 431 K and γ-β at 418 K; both are very sluggish. The a phase does not reconvert to the β phase; it returns to the γ phase below ~418 K. At 298 K the conductivity of the γ phase is 5.3×10^-6 Ω^-1 cm^-1, at 425.5 K, the conductivity of the ß phase is 0.11Ω^-1 cm^-1. The enthalpy of activation of motion of the β phase is 0.77 eV. The γ phase is orthorhombic with a=14.242, b=24.984, c=11.712 Å, probable space groups Cmca or C2ca, and 16 CsCu₄Cl₃I₂ in the unit cell.