Point Defects and Diffusion in Paratellurite

Abstract

Abstract 125Te nuclear spin relaxation (NSR) and electrical conductivity measurements were performed on ultrapure single-crystalline paratellurite (α -TeO2) between about 50 K and the melting point (1007 K) at various oxygen partial pressures (1 bar -10-4 bar). At elevated temperatures the NSR rate 1 / T1 and conductivity σ are caused by the diffusive motion of point defects. From the observed p02-dependence of 1/T1 and σ a defect model is developed which is shown to be consistent with the experimental data. The model involves ionic oxygen interstitials (O″i), doubly charged oxygen vacancies (Vö) and charge-compensating electron holes (h•). The observed pressure dependence suggests that the NSR rate is induced by the motion of Vö while the conductivity 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 and to 4.5 eV for the formation enthalpy of oxygen Frenkel pairs (O″i - Vö). Further, the chemical diffusion coefficient Dc is found to be caused by the ambipolar diffusion of O″i and h• .At 950 K we obtained from both the NSR and conductivity experiments Dc = (1 ± 0.3) • 10-5 cm2/s.