New solid electrolytes for electrochemical sensors of sulphur and indium in various media

To create an electrochemical sensor, selective with respect to sulfur and indium the indium-conductive solid electrolyte (In2S3)1-х(InCl3)х and indium-containing solid electrolyte membranes (InCl3)1-х(MgCl2)х were obtained for the first time. Their structure and transport properties: electrical conductivity, secondary ion transport numbers were studied, the type of ionic conductivity was defined. According to the obtained x-ray pictures, the region of existence of solid solutions based on indium sulfide extends to 7.0 mol.% InCl3. Presumably the dissolution of indium chloride in indium sulfide occurs by the vacancy mechanism of defect formation. The formation of vacancies in the indium sublattice can be a source of cationic ion transport In3 + in this system.The activation energy of electroconductivity of compositions that lie within the area of solid solutions, changes from 1.81 to 1.95 eV for the system (InCl3)1- х(MgCl2)х and from 2.15 to 4.85 eV for the system (In2S3)1-х(InCl3)х. With increase of temperature from 373 to 503 K the electroconductivity increases in the system (InCl3)1-х(MgCl2)х from 10-7 to 10-5 Sm/cm, in the system (In2S3)1-х(InCl3)х from 10 -9 to 10-6 Sm/cm.For solid solutions of indium chloride, in indium sulfide the ion transport numbers are close to unity, so the system (In2S3)1-х(InCl3)х in the range of optimal temperatures and compositions can be used as a solid electrolyte with presumable ion conductivity In3+. The experimental results obtained by Tubandta method confirmed almost unipolar indium cation conductivity (III).The picture of coulometric titration curve indicates the existence of bilateral field homogeneity on the basis of In2S3, and the areas with excess and lack of indium are symmetrical, that is indium sulfide is described by In2±δS3. The width of the homogeneity region is 0.43%, which indicates the deviation from stoichiometry δ = 2,2 · 10-3 of atomic fractions of indium.