The Study Of CdO Low Density Allotropes By First-principles Calculations

With the improvement of the experimental level,it has become possible to design cluster materials with specific functions by using nanoclusters as the building blocks and adopting the"bottom-up"assembly method.Compared with common materials,cluster assembled materials can not only reflect the properties of the building blocks,but also control the properties of the materials by changing the size of the original primitives or the interaction between the blocks.Therefore,the cluster assembled method is considered to be one of the most promising ways to develop and design new functional materials.Four kinds of novel CdO low-density allotrope phases are obtained by using the experimentally synthesized magical cage cluster Cd₁₂O₁₂ as the building blocks with different stable interaction ways by"bottom-up"assembled approach?such as SOD,LTA,FAU and EMT?.First,these new structures are more stable in energy than the B2 phase.Second,the SOD phase with the lowest energy has good mechanical,dynamic and thermodynamic stability?>500K?.More interestingly,the SOD phase is a very ductile direct bandgap semiconductor with a band gap of 1.57 eV.This optimal optical bandgap makes it a very promising photovoltaic material.Finally,SOD phase also has a high carrier mobility(up to 9.6×10³cm²v^-1s^-1),which is about three times higher than the traditional B1-CdO phase,and has very good transport characteristics.Based on cluster-assembled bottom-up approach,we obtain five kinds of stable low-density CdO polymorphs(for exmaples Cd₂O₂,Cd₄O₄,Cd₆O₆,Cd₁₂O₁₂ and Cd₁₆O₁₆)with small-sized magic clusters?Cd₈O₈ and Cd₉O₉?as the building blocks.The calculations show that all new phases have good mechanical,dynamic and thermodynamic stability?>500K?and are more stable than the traditional B2-CdO phase.Among them,the energy of the Cd₂O₂ phase is almost identical to the most stable B1-CdO phase in room temperature.It can be seen from the comparison of the corresponding mechanical parameters that all the new phases have higher flexibility ductility and anisotropy than the conventional B1-CdO phase.Finally,by the analyzing of electronic properties,most of the assembled phases are indirect bandgap semiconductors,but the Cd₁₆O₁₆6 phase is a semiconductor with a direct band gap of1.58 eV,which is very close to the optimal optical bandgap value.So it is also a good optoelectronic material.