ELECTRON-TRANSFER AND ELECTRONIC-STRUCTURE OF KCUFES2

The electron transfer that occurs in the insertion of potassium in CuF eS2 has been analyzed by two different techniques. The binding energie s of the core electrons of CuFeS2, KCuFeS2 and K-x CuFeS2 (x approxima te to 0) has been studied by XPS experiments, while the band structure of these phases has been investigated by tight-binding EH calculation s. Both experimental and numerical results strongly support the belief that the insertion reaction induces a redox process in the starting C uFeS2, by which the Fe3+ ions are reduced to Fe2+. Upon removal of the potassium ions, the Fe2+ ions are oxidized to Fe3+. Copper atoms do n ot participate in the redox reaction.