The solid electrolyte system RbCu₄Cl₃(I_2-xCl_x), 0 ≤ x ≤ 0.40

Abstract

The stoichiometric solid electrolyte, RbCu₃Cl₃I₂, can be converted, bycold-work, to a new low symmetry phase with the probable compositionRbCu₄Cl₃(I_1.96Cl_0.04) (and very small amounts of CuI and probably,Rb₂Cu₃Cl₅). The new phase has a crystal structure which appears to berelated to that of the cubic phase. It transforms rapidly to the cubic phasewith formula RbCu₄Cl₃(I_1.96Cl_0.04) at temperatures above 75°C. The newphase is stable in a very narrow temperature range, almost surely not widerthan 0°-35°C. It has a conductivity of 1.5 × 10^-4 Ω^-1 cm^-1 at 298 K. StoichiometricRbCu₄Cl₃I₂ is thermodynamically stable in the narrow temperaturerange 200° ± 15°C. The solid solution range RbCu₄Cl₃(I_2-xCl_x) 0.00 ≤ x ≤ 0.40 ± 0.01 has been confirmed. For 0.02 ≤ x ≤ 0.40, the materials appearto be stable from at least 78 K to their preparation temperatures which dependon x. None of these can be made to convert to the new phase; that isto say, the only established route to the new phase is through cold-working ofthe stoichiometric phase.