We have examined methods for controlling the morphology and microstructure of ceramic particles produced by spray pyrolysis. A variety of materials were examined including SrTiO3and BaTiO3 and the oxides of Al, Mg, Zn, Pd, V, Mo, and Bi. The morphology of the particles was influenced by using colloidal precursors in combination with molecular precursors for particle generation. Slow drying rates obtained by using high relative humidities and controlled axial temperature gradients did not influence particle morphology for the systems and conditions studied. The microstructure of Al2O3, V2O5, and PdO particles was controlled by varying the temperature to provide nanocrystalline or single-crystal particles. Evaporation and condensation of volatile species such as MoO3 and V2O5 dramatically modified particle microstructure and morphology.

Single crystals of Ca2La8(SiO4)6O2, with 1% Nd substituted for La, were irradiated with 0.8 MeV Ne+ and 1.5 MeV Kr+ ions over the temperature range from 15 K to 773 K. The irradiations were carried out using the HVEM-Tandem Facility at Argonne National Laboratory. The structural changes and the ion fluence for complete amorphization were determined by in situ transmission electron Microscopy. The ion fluence for complete amorphization increased with temperature in two stages associated with defect annealing processes. The critical temperature for amorphization increased from -360 K for 0.8 MeV Ne+ to -710 K for 1.5 MeV Kr+. During in situ annealing studies, irradiation-enhanced recrystallization was observed at 923 K. Spatially-resolved fluorescence spectra of the Nd ion excited with 488.0 nm laser excitation showed marked line-broadening toward the center of the amorphous regions. Initial Measurements indicate the subtle shifts of the 9I9/2 groundstate energy levels can be measured by pumping directly into the excited state 4F3/2 Manifold suggesting that the line broadening observed originates from a distribution of geometrically distorted Nd sites.

Single crystals of the silicate neptunite were irradiated with 600 keV Ar2+ and 1.5 MeV Kr+ and analysed by transmission electron microscopy. Amorphization was observed in a surface layer several hundred angstroms thick following Ar2+ irradiations up to 5.0×l013 Ar/cm2, yet the Ar2+ ions travelled an average of 1/2 μm in depth. The microstructure of the amorphous surface layer depends on the ion fluence, but the amorphous layer thickness remained constant. At the highest fluence, a narrow region below the amorphous layer shows a brittle-to-ductile strain transition, due to tensional volume-expansion of the adjacent ductile amorphous layer. With 1.5 MeV Kr1+, amorphization of the electron transparent region was completed after a fluence of 1.7×l014 Kr+/cm2, and no further damage was observed up to 5.1×1015 Kr+/cm2. However, following a low fluence of 2.0×1011 Kr+/cm2, a single crystal of neptunite became a polycrystalline aggregate (grain size 10 nm) within 7 days of room temperature aging.

Ion-beam-induced amorphization in single crystal a-SiC has been studied as a function of temperature. Specimens have been irradiated with 1.5 MeV Xe' ions over the temperature range from 20 to 475 K using the HVEM-Tandem Facility (ANL), and the evolution of the amorphous state has been followed in situ in the HVEM. Specimens also have been irradiated at 170, 300, and 370 K with 360 keV Ar' ions, and the damage accumulation process followed in situ by Rutherford backscattering spectroscopy/channeling using the dual beam facilities at the Ion Beam Materials Laboratory (LANL). At 20 K, the displacement dose for complete amorphization is 0.25 dpa and increases with temperature in two stages. The activation energy associated with the simultaneous recovery processes above 100 K is 0.12 ± 0.02 eV. The critical temperature above which amorphization does not occur is 485 K under the 1.5 MeV Xe' irradiation conditions. Ion channeling results suggest that the rate of simultaneous recovery increases with temperature only above a critical damage level. Raman spectroscopy indicates that rapid chemical disordering occurs during irradiation.

Single crystals of CaF2 were irradiated with 5.8 MeV alpha particles from a 244Cm source, and the absorbance spectra were recorded as a function of dose and temperature. Absorbance from the metal colloid band increases with dose at all temperatures. The colloid band exhibits a sharp increase in rate of growth over a narrow temperature range with a peak at 150°C. After a dose of 1.4 x 1016 α/cm2 at 150°C, the intensity of the colloid band is a factor of 7 to 8 higher than the intensity produced at 100 and 200°C. The optimum temperature (150°C) for colloid formation in CaF2 under the alpha-irradiation conditions (σ5 x 108 rad/h) of this study is significantly higher than the peak temperature (60°C) reported for colloid production in electron irradiated CaF2 at slightly higher dose rates (σ109 rad/h). Cryogenic transmission electron microscopy of the irradiated crystals reveals dislocation loops and small dark clusters as the dominant microstructural features.