Impurity centers and electronic band structure of lithium-doped cadmium oxide

Prepared by the precursor method, lithium-doped cadmium oxide samples were synthesized using mixed formates of Cdi(1-x)Li(x)(HCOO)(2)center dot 2H(2)O (0 <= x <= 0.075) as a precursor. NMR spectra were obtained on the lithium nuclei incorporated in cadmium oxide; and it is demonstrated that there is only one type of impurity centers to be found. The first-principle method using a projector augmented wave (PAW) approach is applied to carry out electronic band structure calculations and to analyze optical absorption spectra for the cases of lithium atoms occupying interstitial sites and of lithium atoms substituting for cadmium or oxygen atoms. Calculations are carried out to determine energy-efficient preferences for sites of impurity centers, which indicate as the most probable the presence of lithium atoms at the interstitial sites, with vacancies observed in the cadmium sub lattice. The presence of lithium atoms at the interstitial sites appears to be explaining the conductivity increase and the red-shift of the absorption edge observed in experiments.