pDoping in Expanded Phases of ZnO: AnAb InitioStudy

Abstract

The issue of p doping in nanostructured cagelike ZnO is investigated by state-of-the-art calculations. Our study is focused on one prototypical structure, namely, sodalite, for which we show that p-type doping is possible for elements of the V, VI, and VII columns of the periodic table. However, some dopants tend to form dimers, thus impairing the stability of this kind of doping. This difference of behavior is discussed, and two criteria are proposed to ensure stable p doping.

Superconductivity in an expanded phase of ZnO: anab initiostudy

“…This is experimentally proven for other compounds, such as Si clathrates [39]. In a previous work [35], we predicted that stable p-doping could be achieved in sodalite ZnO. Doped structures turned out to be even more stable than the undoped ones for some impurities.…”

“…Sodalite ZnO remains a iono-covalent material with a ionicity very close to the one of the wurtzite structure (the Philipps ionicity of wurtzite ZnO is close to 0.616 [43]). Also the direct bandgap of sodalite ZnO is close to the one of wurtzite ZnO [35]. This can be explained by the similar sp 3 bonding and bonding distance of the wurtzite and sodalite phases.…”

“…Furthermore, the deformation of the cage is strong and anisotropic. The inspection of the lattice distortions reveals repulsion between O and dopant atoms, while Zn atoms basically remain at their initial positions [35]. These deformations point to a strong hybridization between the electrons of the dopant and the ones of ZnO.…”

“…Note that the BCT phase of ZnO has already been identified experimentally [36,37]. However, although also the BCT phase is a cage-like structure, the volume of its unit cell is small and comparable to the one of wurtzite [35]. As a consequence, heavy endohedral doping is expected to be difficult.…”

“…However, other cage-like allotropes are under study. For instance, calculations have shown that the body-centered tetragonal (BCT) structure is more stable than the sodalite structure, with a cohesive energy very close to the wurtzite one (+0.030 meV/ZnO) [35]. Note that the BCT phase of ZnO has already been identified experimentally [36,37].…”