| The thesis is concerned with the development of new IR transmitting materials for the 8-14 micrometer atomspheric window. The strategy was to investigate, in detail, the synthesis, crystal chemistry, processing, optical, and electronic properties of the rare earth sulfide as candidate materials.;The rare earths crystallize in five known structures. Study of their temperature stabilities during long reaction times showed that alpha (orthorhombic, Pnma) exists as the low temperature form, and gamma (cubic, I;Extremely fine-grained precursor oxides were synthesized by evaporative decomposition of solution. An ultrasonic dispersion of aqueous nitrate salts is misted into a hot walled furnace. The 2-5 micrometer resulting oxides were predominantly well-crystallized spherical particles. The sesquisulfides could be readily synthesized by direct reaction of the oxides with flowing H;These reactive, fine-grained, EDS-derived sulfides could be sintered into ceramic compacts that achieved 92-98 percent of theoretical density. Sintering temperatures from 1200;The measurement of the electronic absorption edge yielded band gaps of 1.6-2.6 eV. The first-order transverse and longitudinal phonon frequencies obtained by specular reflectance FTIR spectroscopy occurred in the range of 200 cm;The evaluation of the rare earth sesquisulfide shows, from the stability, processing electronic and optical properties, these materials have the characteristics required for IR window materials. |
