New Optical Materials for the Long-Wave (8-12 Microns) Region: Design Criteria for the Solid-State Chemist

Abstract : Certain applications that utilize long-wavelength (8-12 micron) infrared (LWIR) windows require environmental durability and mechanical strength in addition to infrared optical transparency; i.e., the window-materials must simultaneously serve as optical and structural ceramics. The fundamental requirement of optical transparency in the long-wavelength region eliminates from consideration all well-known ceramic materials such as oxides, nitrides, and other light-anion compounds, making this a particularly difficult materials problem. The structure-property relationships and chemical rationale used to guide both the screening of known compounds and the synthesis of new compounds likely to possess the desired properties rely on factors such as atomic mass, electronic configuration, coordination number, and crystal structure-type. The resulting criteria have directed our efforts in the synthesis and characterization of a number of ternary indium sulfide phases and calcium yttrium sulfide systems.