POINT-DEFECTS AND DIFFUSION IN PARATELLURITE

Te-125 nuclear spin relaxation (NSR) and electrical conductivity measu rements were performed on ultrapure single-crystalline paratellurite ( alpha-TeO2) between about 50 K and the melting point (1007 K) at vario us oxygen partial pressures (1 bar -10(-4) bar). At elevated temperatu res the NSR rate 1/T1 and conductivity sigma are caused by the diffusi ve motion of point defects. From the observed p(o2)-dependence of 1/T1 and sigma a defect model is developed which is shown to be consistent with the experimental data. The model involves ionic oxygen interstit ials (O''(i), doubly charged oxygen vacancies (V(o).. and charge-compe nsating electron holes (h.). The observed pressure dependence suggests that the NSR rate is induced by the motion of V(o).. while the conduc tivity is due to the mobility of h.. Evaluation of the data leads to 3 .3 eV for the incorporation enthalpy of oxygen on interstitial sites a nd to 4.5 eV for the formation enthalpy of oxygen Frenkel pairs (O''i - V(o)..). Further, the chemical diffusion coefficient D(c) is found t o be caused by the ambipolar diffusion of O''i and h.. At 950 K we obt ained from both the NSR and conductivity experiments D(c) = (1 +/- 0.3 ). 10(-5) cm2/s.