| Popis: |
Energy band structure calculations are carried out on three tetragonal dioxides belonging to the IV group (SnO2, GeO2, β-PbO2) with the help of the KKR method. The results obtained are compared with many experimental results in order to try to make a synthesis of the optical properties of these compounds and to relate them to our theoretical results; In fact, the complexity of their unit cell and the difficulty to obtain the energy levels near the energy band gap by optical measurements seem to be responsible for the large discrepancies of results in literature concerning these compounds. Our results have confirmed the presence of the expected Γ+1 and Γ+4 states at the bottom of the conduction band; they have also given a valence band model that does not completely agree with any of the various models of energy levels lying in the vicinity of the energy gap. Moreover, our results seem to prove that no indirect transition exists neither in SnO2, nor in β-PbO2. At last, among several results that can be drawn from our calculations, one of the most significant is that the three compounds exhibit a strong dischroism, since the E⊥C transition has a weaker energy than the E∥C transition in SnO2 and GeO2, and conversely in β-PbO2. |
