Ab initio molecular dynamics study of amorphous CdTeO_x alloys: Structural properties

The structural short-range order of amorphous compounds with the composition CdTeOx (a -CdTeOx) is investigated by means of ab initio molecular dynamics. The interatomic forces have been calculated using a plane-wave pseudopotential implementation of density-functional theory. Molecular dynamics has been performed in the nearly-microcanonical ensemble using the Berendsen algorithm to keep the systems at the desired temperature. The compounds are characterized using the pair distribution functions, angle distribution functions, coordination numbers, histograms of coordination numbers, and a description of the molecular units of the compounds. According to our simulations, a-CdTeO and a -CdTeO2 are more disordered than a -CdTeO0.2 and a -CdTeO3. In a -CdTeO0.2, the most abundant clusters are TeCd4, CdTe4, TeCd3, and CdTe3 O. In the case of a-CdTeO and a -CdTeO2, having structural units of types similar to those found in crystalline phases of the Cd-Te-O system, they show no predominant type of cluster. This absence of predominant building blocks is a signature of chemical disorder, and it seems that Te and O atoms can be freely exchanged, as well as Cd to a lesser extent. Finally, in a -CdTeO3, the most abundant clusters are CdO6, CdO5, TeO3, and TeO4.