The solid electrolyte system RbCu₄Cl₃(I₂−_xCl_x), 0≤x≤0.40 I. Stability

The stoichiometric solid electrolyte, RbCu3Cl3I2, can be converted, by cold‐work, to a new low symmetry phase with the probable composition RbCu4Cl3(I1.96Cl0.04) (and very small amounts of CuI and probably, Rb2Cu3Cl5 ). The new phase has a crystal structure which appears to be related to that of the cubic phase. It transforms rapidly to the cubic phase with formula RbCu4Cl3(I1.96Cl0.04) at temperatures above 75°C. The new phase is stable in a very narrow temperature range, almost surely not wider than 0°–35°C. It has a conductivity of 1.5×10-4 Ω -1cm-1 at 298 K. Stoichiometric RbCu4Cl3I2 is thermodynamically stable in the narrow temperature range 200° ± 15° C. The solid solution range RbCu4Cl3(I2-xClx)0.00 ≤ x ≤0.40 ± 0.01 has been confirmed. For 0.02 ≤ x ≤ 0.40, the materials appear to be stable from at least 78 K to their preparation temperatures which depend on x . None of these can be made to convert to the new phase; that is to say, the only established route to the new phase is through cold‐working of the stoichiometric phase