DEFECT STRUCTURE AND CHARGE-TRANSPORT IN PURE THORIUM-OXIDE AND IN THO2-LN2O3 SOLID-SOLUTIONS (LN = LA OR ND)

It was seen when investigating the defect structure and conductivity o f pure thorium oxide and of ThO2 doped with rare-earth metal oxides Ln 2O3 (where Ln = La or Nd) that, (a) the model that was suggested for t he formation of structural interstitials with H centers provides a sat isfactory explanation for the observed relation between conductivity a nd oxygen partial pressure, p(O2), (b) conduction in pure ThO2 is of t he hole type at oxygen pressures of 10(-2) greater-than-or-equal-to P( O2) greater-than-or-equal-to 10(-7) Mpa, and its values are readily de scribed by the power law, sigma(h) approximately P(O2)1/4, and (c) sol id solutions on the basis of ThO2 containing Ln2O3 are predominantly i onically conducting at intermediate oxygen pressures (P(O2) < 10(-7) M Pa); p-type electronic conduction will appear only at high oxygen part ial pressures.