Intrinsic defect model of paratellurite ( <i>α</i> -TeO ₂ ) based on the charge neutrality condition and density-functional calculations

The intrinsic defect-formation energies and equilibria of the<i>α</i>phase of TeO₂(paratellurite) at room temperature were studied theoretically by means of calculations based on density-functional theory with a semilocal exchange-correlation functional. The self-consistent solution of the electroneutrality condition led to the equilibrium concentrations of both ionic and electronic defects for the admissible range of the elemental chemical potentials. The calculated charge-transition levels for the ionic defects were found to lie deep in the electron gap. Similarly, the equilibrium Fermi level was invariably located in the mid-gap region something which is consistent with a strong insulating character of<i>α</i>-TeO₂at this temperature range. The final results show a dominance of the oxygen defects (monovacancy and interstitial) with their electronic structure examined by means of the projected and total densities of states. The density of the electronic defects (electrons and holes) was found to be very small, nonetheless, their presence assured the necessary charge compensation. The present findings are also discussed with respect to existing conductivity and spin-resonance studies of<i>α</i>-TeO₂and electron irradiation experiments where paramagnetic (spin-1/2) oxygen-vacancy defects were resolved.