Insulator to metal transition of WO3 epitaxial films induced by   electrochemical Li-ion intercalation
  We investigated systematic evolutions of structural and electronic properties of LixWO3 films, induced by Li-ion electrochemical reactions. Chronoamperometric Li-ion intercalation could control the amount of Li content up to x ~ 0.5. The resistivity abruptly decreased with increasing x and the films underwent an insulator to metal transition (IMT) within a range of 0.2 < x < 0.24, which was consistent with IMT of cubic NaxWO3. The X-ray diffraction analyses revealed the coexistence of tetragonal and cubic phases across IMT, suggesting that the alkaline-ion content was a primary factor for metallic conductivity in the ReO3-type WO3 system. 
Kohei Yoshimatsu, Takuto Soma, Akira Ohtomo
cond-mat.mtrl-sci