Small-polaron absorption in W x Mo1–x O3

Optical absorption and reflection spectra of WO3, WO3 : H0, W x Mo1–x O3 : H0, and sub-stoichiometric ternary oxides have been measured. In WO3, the free-carrier absorption at room temperature switches over to small (or intermediate) polaron absorption near 0·7 eV at low temperatures. In fully oxidized ternary oxides doped with hydrogen, quasi-localized charge carriers with optical transition energies between 1·24 and 1·42 eV have been found. Sub-stoichiometric compounds with extended defect structures like crystallographic shear planes or tunnel structure reveal intervalence transitions including Mo5+, W5+, Mo6+ and W6+ states. An energy level scheme is discussed including the effects of metal–hydrogen interaction.