First-principles study of mechanical and optical properties for ZnS_{1− x}O_x alloying compounds

An excellent infrared window material should have both high transmittance and good mechanical strength to adapt to applications in harsh environments. In this report, we use first-principles calculations to investigate the effect of oxygen alloying on the mechanical and optical properties of the well-used infrared window material ZnS. We have found that with increasing oxygen content, the mechanical properties including elastic constants, bulk modulus, shear modulus, Young's modulus of ZnS_{1− x}O_x compounds are improved compared to the pristine phase. Meanwhile, the infrared optical transmittance of the system is retained with changing oxygen compositions. We have also considered the influence of oxygen/sulfur vacancy defects in the system. We have observed that the optical transmittance of the system is degraded upon induction of vacancies. These results have revealed that the mechanical properties of optical materials can be effectively enhanced with appropriate alloying, but there are also challenges in practice due to the presence of defects. Our investigations can guide the design of these infrared optical materials in special applications such as aircraft and space systems.