Infrared-transparent glass ceramics: An exploratory study

• Fully ceramized long-wave infrared transmitting glass ceramics are needed.
• Ga2S3–La2S3 phase separates; including CaS or ZnS suppresses this or causes crystallization.
• GeS2–La2S3 is very difficult to produce due to decomposition of constituents.
• GeS2–Ga2S3–CdS is a good glass former, made from elements, and has a good IR-transparency.
• Raw material choice (elements or sulfides) & purity (e.g. O in La2S3) are critical for glass formation.

In this work, the vision and need for a fully ceramized long-wave infrared (LWIR)-transmitting glass ceramic have been articulated. Three sulfide systems were explored including two with La2S3 in hopes of imparting strong bonds from this refractory sulfide, and two containing GeS2 in hopes of widening the glass-forming region. Attempts were made to produce glasses in the Ga2S3–La2S3–(ZnS,CaS) system, the GeS2–La2S3 system, and the GeS2–Ga2S3–CdS system. Water quenching produced glasses of Ga2S3–La2S3–CaS and GeS2–Ga2S3–CdS. Microstructural and thermal analyses were used to explore nucleation and growth in these systems and infrared transmission and mechanical hardness showed potential for LWIR window use. The GeS2–Ga2S3–CdS system showed good LWIR transmission and pre-crystallized hardness superior to chemical vapor deposited ZnS. The Ga2S3–La2S3 glasses did not appear to be viable candidates at this time due to a small temperature window between crystallization and glass transition temperatures and problems with oxygen contamination in the La2S3 source. Suggestions are made for two alternative methods for producing fully ceramized LWIR-transmitting glass ceramics.