Copper sulfide-selenide solid solutions

Figure II.8.3 gives two examples, one for the dependence of a voltammetric peak potential of copper reduction on the composition of copper sulfide-selenide solid solutions, and one for the dependence of the formal potentials (mid-peak potentials from cyclic voltammetry) of mixed iron-copper hexacyanoferrates on the composition of these compounds. The copper sulfide-selenides behave in very nonideal fashion, whereas the solid solution hexacyanoferrates give, within the limit of experimental errors, an almost linear dependence. These and other examples [18-21] are well suited to show that by voltammetric measurements of immobilized microparticles it is extremely facile to answer the two questions, is it a solid solution or not, and what is its composition.

Electrochemical methods can be applied to the determination of the composition of solid phases as well as mixtures of solids [224-228], The first situation is illustrated in Fig. 4.1, where cathodic voltammograms of CuS, CuSe, and a solid phase of composition CuSeoASo.e reported by Meyer et al. [227] are shown. This last can be described as a solid solution formally regarded as a copper sulfide, in which 40% of sulfide ions have been replaced by selenide ions. The new phase produces a voltammetric peak at a potential intermediate between those for CuS and CuSe. 

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