Coulometric titration of copper in Cu xMo 6S 8−y(0⩽y⩽0.4) with solid Cu-electrolyte Rb 4Cu 16I 7Cl 13

Abstract

In order to determine the copper content x of copper Chevrel compound Cu x Mo 6S 8−y(0⩽ y⩽0.4) as a function of copper activity a Cu and sulfur deficit y, a solid state electrochemical cell, Cu/Rb 4Cu 16I 7Cl 13/Cu x Mo 6S 8−y/Pt, was constructed and coulometric titration studies were made at 400 K. For the evaluation of the coulometric titration data, measurements were made on the electronic conductivity of copper-ion conductor Rb 4Cu 16I 7Cl 13. Also, a brief investigation was made on the condition of formation of single phase Chevrel Cu x Mo 6S 8−y with varying x and y at 1000°C. The structural change of Cu x Mo 6S 8−y with a change in x and y was studied by the X-ray diffraction method. It was found that x for constant a Cu decreases with increasing y. The maximum value x max of x in Cu x Mo 6S 8−y in equilibrium with metallic copper was found to be expressed by x max =-( 10 3 )y+5 . In the region of y<0.3, x max exceeded 4, contrary to a presupposition that x max is less than 4. X-ray analysis revealed that most of the copper Chevrel compounds denoted by Cu x Mo 6S 8 so far were sulfur deficient ones with y≅0.4. The importance of sulfur deficit on the properties of the copper Chevrel compound was emphasized.