Lanthana-strengthened yttria is of interest for infrared applications because of its high strength, long wavelength cutoff (8 pm), and low emissivity. The optical, thermal, and mechanical properties of the family of La203-strengthened Y203 have been characterized. The properties can be tailored to suit the requirements of specific applications by adjusting composition and processing parameters. The La203 acts as both a densification aid during fabrication and an agent for microstructural control. Since both strength and toughness depend on microstructure, the La203 allows significant strength enhancement, an important factor for window applications. Theoretical parameters have also been calculated to aid in the assessment of relative resistance to thermal shock fracture initiation and propagation. These calculations reveal potential inconsistencies that must be resolved by experimental testing.

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Experiments aimed at improving the physical properties of transparent polycrystalline lanthanastrengthened yttria (LSY) infrared windows and domes were conducted. The objective was to enhance the thermal shock resistance for aggressive aerothermal environments. The approach included improving the average equibiaxial flexure strength, Weibull modulus, and other relevant physical properties. Initial results of an extensive study on polishing and post-fabrication treatment along with improved powder processing showed an -30% strength improvement without sacrifice in optical properties, leading to an appreciable increase in the calculated survivability. LSY with a low lanthana content significantly enhanced predicted survivability.

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Lanthana -doped yttria has a number of favorable intrinsic properties for infrared window applications. La2O3 is a sintering aid which makes possible pore -free transparent polycrystalline near-net -shape domes and windows by a unique transient second solid -phase sintering technique. This same second phase can be retained by special anneals to impart mechanical toughening by a second -phase crack -deflection mechanism. Transmission electron microscopy has been utilized to characterize crack deflection and the complex second phase nucleation and growth process. Reduced absorption coefficients have been achieved through improved processing, 011-removal, and stoichiometry adjustments. The trade -off between mechanical and optical properties has been quantified, and a region of promising compromise identified.