Cluster-Assembled Semiconductor CdO Polymorph with Good Ductility, High Carrier Mobility, and Promising Optical Properties

Recently, the magic cluster Cd12O12 with cagelike structure has been experimentally synthesized, which is expected to serve as building blocks of desirable new materials. On the basis of the cluster-assembled bottom-up approach, herein, we construct four kinds of stable low-density CdO polymorphs (i.e., SOD, LTA, FAU, and EMT), which are energetically more stable than the high-pressure B2-CdO phase. In the framework, the cage structure of the building block Cd12O12 is well preserved for all of these new phases. Our calculations show that the SOD phase with the lowest energy is mechanically, dynamically, and thermally stable (at least to 500 K). Remarkably, the SOD is a very ductile (77 GPa bulk modulus) semiconductor with a direct band gap of 1.57 eV. This optimal gap makes the SOD a promising photovoltaic material, which would have a large absorption in the visible light region. Furthermore, the calculations of transport properties from the deform potential approximation reveal that the SOD phase has not only lower effective mass but also higher electron-dominated mobility (up to 9.6 X 10(3) cm(2) V-1 s(-1)) with respect to that of the conventional CdO phases. These results highlight a bottom-up way to obtain the desired optoelectronic materials with the cluster serving as building blocks.