Thin films of pure and Nb-doped or Cr-doped material were deposited by radio-frequency sputtering from metallic Ti, Ti-Nb or Ti-Cr mosaic targets, in an Ar-O2 atmosphere, onto fused silica substrates. The conductivity was measured at 1250K, under O partial pressures of 10-15 to 105Pa. The high-temperature defect structure, and the mechanism of incorporation of the Nb and Cr dopants, were determined. The effect of H defects upon the electrical properties was studied. It was found that Cr(III) ions substituted for Ti ions and formed acceptor centers, CrTi'. The incorporation of Cr led to an increase in the ionic defect concentration, and shifted the n-p transition point to lower O pressures. On the other hand, Nb5+ ions acted as donors (NbTi˙). Their incorporation led to an increase in electronic conductivity and to a decrease in ionic conductivity.

Radecka, M., Rekas, M.: Solid State Phenomena, 1994, 39-40, 135-8