The auto-localization of free electrons at WO42- complex anions was demonstrated by means of electron spin resonance measurements It was known that the WO43- center was a shallow donor, with its energy level situated some 0.05eV below the bottom of the conduction band. At temperatures of 50 to 60K, the captured electrons were de-trapped and the formation of other paramagnetic centers occurred. In La-doped material, an enhanced cross-section (with respect to that for undoped samples) for electron-trapping by MoO42- impurity centers was found. No intrinsic O hole and/or Pb3+ centers were revealed.

V.V.Laguta, J.Rosa, M.I.Zaritskii, M.Nikl, Y.Usuki: Journal of Physics - Condensed Matter, 1998, 10[32], 7293-302