Electrical conductivity and phase transitions of the solid electrolyte system (Cs<SUB>1-y</SUB>Rb<SUB>y</SUB>)Cu<SUB>4</SUB>Cl<SUB>3</SUB>(I<SUB>2-x</SUB>Cl<SUB>x</SUB>)

Results of electrical conductivity measurements, thermal analysis, and X-ray diffraction studies indicate the existence of four phases, between 295 K and the melting points, in the system (Cs1-yRby)Cu4Cl3I2. These phases are designated &#945;, &#225; &#946;, &#947; in order of decreasing temperature. The &#945; phase is isostructural with &#945;-RbAg4I5; the &#225; phase is also cubic and very likely belongs to space groupP213, a subgroup ofP4132 andP4332 to which the &#945; phase belongs. There is a high probability that the &#225; &#8594; &#945; transition is continuous. The &#225; &#8594; &#945; transition is not discernible in the conductivity measurements or thermal analysis; therefore the line of &#225;-&#945; transitions is presently unknown. The &#946; phase transforms to the &#225; and the &#947; phase transforms to the &#946; phase wheny &#8804; 0.36; the &#947; phase transforms to the a phase wheny &#8805; 0.36. That is, there is a triple point aty = 0.36, T = 399K. The &#947;-&#946;, &#946;-&#945;', and &#947;-&#945; transitions are all hysteretic and are therefore first order. The conductivities of the &#946; phases are relatively low and the enthalpies of activation relatively high. The conductivity of the &#946; phase decreases with increasingy. The &#946; phase probably belongs to space groupR3, in which the Cu+ ions can be ordered. The &#945; and &#225; phases are the true solid electrolytes; the conductivities are high, &gt;0.73 &#937;-1cm-1 at 419 K, and the enthalpies of activation of motion of the Cu+ ions low, 0.11 eV. In the system CsCu4Cl3(I2-xClx), 0 &#8804; x &#8804; 0.25, the Cl- for I- substitutions affect the transitions to only a small extent relative to the stoichiometric compound. The &#946; phase occurs for allx and transforms to &#225;