Determination of electronic structure by impedance spectroscopy

We present a novel method, based on electrochemical intercalation and impedance spectroscopy, to determine the electronic density of states of disordered transition metal oxides. Specifically, we have determined the “electrochemical density of states” of tungsten and iridium oxide thin films over energy ranges as wide as 1–2 eV. Our experimental results show a number of qualitative features exhibited by state-of-the-art band structure computations. Differences in details are probably due to the disordered, porous and sometimes amorphous nature of our films. The results suggest that the impedance spectroscopy method can be used to obtain the density of states only if the conduction band states are localized. The electrochemical density of states is often smaller than the computed one due to kinetic effects, i.e. very slow relaxations of the charge carriers. Nevertheless, our sensitive method opens new vistas for studying the electronic structure of disordered materials.