<title>New Infra-Red Window Materials</title>

The alkaline earth-rare earth sulphide family has been identified as an interesting new class of materials with potential for application as broad band infra-red windows. These sulphides are generally refractory and show potential for exhibiting better thermal and mechanical properties than the binary zinc chalcogenides, zinc sulphide and zinc selenide, both currently available broad band window materials at an advanced stage of development. Within this ternary rare earth sulphide family attention has been focussed on compounds with the cubic thorium phosphide structure, and in particular upon calcium lanthanum sulphide, CaLa2S4. This paper describes the preparation of CaLa2S4 ceramics from ternary sulphide powders using a variety of densification techniques and also reports the results of some initial property determinations.