The properties of samples of the form, Cu4Rb1-xKxBr3I2, which had been obtained via the isovalent isomorphous replacement of Rb by K were determined. An X-ray diffraction study was made of solid solutions, with x-values of 0.25, 0.5 or 0.75, at temperatures ranging from 297 to 480K. The unit-cell parameter of Cu4Rb0.5K0.5Br3I2 at 473K was found to be 1.041nm. Conductivity measurements were performed after cooling from 502K to the decomposition temperature, where a marked decrease in conductivity occurred. The results for Cu4Rb0.5K0.5Br3I2, at temperatures above 458K, could be described by:

σT (SK/cm) = 4.36 x 103 exp[-0.091(eV)/kT]

At temperatures of between 428 and 458K, the results could be described by:

σT (SK/cm) = 2.31 x 104 exp[-0.158(eV)/kT]

V.V.Ivanov: Izvestiya Akademii Nauk SSSR - Neorganicheskie Materialy, 1992, 28[1], 182-3 (Inorganic Materials, 1992, 28[1], 149-50)