Electrical conductivity and phase transitions of the solid electrolyte system (Cs1-yRby)Cu4Cl3(I2-xClx)

Geller, S. ; Ray, A. K. ; Nag, K. (1983) Electrical conductivity and phase transitions of the solid electrolyte system (Cs1-yRby)Cu4Cl3(I2-xClx) Journal of Solid State Chemistry, 48 (2). pp. 176-188. ISSN 0022-4596

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/002245...

Related URL: http://dx.doi.org/10.1016/0022-4596(83)90073-7


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 α, á β, γ in order of decreasing temperature. The α phase is isostructural with α-RbAg4I5; the á phase is also cubic and very likely belongs to space groupP213, a subgroup ofP4132 andP4332 to which the α phase belongs. There is a high probability that the á → α transition is continuous. The á → α transition is not discernible in the conductivity measurements or thermal analysis; therefore the line of á-α transitions is presently unknown. The β phase transforms to the á and the γ phase transforms to the β phase wheny ≤ 0.36; the γ phase transforms to the a phase wheny ≥ 0.36. That is, there is a triple point aty = 0.36, T = 399K. The γ-β, β-α', and γ-α transitions are all hysteretic and are therefore first order. The conductivities of the β phases are relatively low and the enthalpies of activation relatively high. The conductivity of the β phase decreases with increasingy. The β phase probably belongs to space groupR3, in which the Cu+ ions can be ordered. The α and á phases are the true solid electrolytes; the conductivities are high, >0.73 Ω-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 ≤ x ≤ 0.25, the Cl- for I- substitutions affect the transitions to only a small extent relative to the stoichiometric compound. The β phase occurs for allx and transforms to á.

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