Thin films by consolidation and sintering of nanocrystalline powders

Abstract

Nanocrystalline CeO 2 and Y 2O 3-doped CeO 2 powders (particle size of 10–15 nm) were prepared under hydrothermal conditions at temperatures between 100 and 300 °C. X-ray diffraction and transmission electron microscopy revealed that the particles were crystalline. The particle size distribution followed approximately the Lifshitz-SlyozovWagner theory for Ostwald ripening controlled by the diffusion step. Powder compacts were sintered to nearly full density below 1350 °C. Thin adherent films (0.5 to 1 μm thick). on rigid substrates were prepared by spin-coating or dip-coating of stabilized suspensions, followed by drying and sintering. Dilute suspensions in aqueous solvents were stabilized electrostatically at pH values of 3.5 to 4. However, increasing particle concentration produced flocculation. Higher particle concentrations can be achieved without flocculation through the use of sterically stabilized suspensions with polyvinylpyrrolidone (PVP) as a dispersant. With these suspensions, homogeneous films were deposited on porous or dense substrates. The shrinkage kinetics of the adherent films were approximately the same as those for the powder compacts. The use of nanocrystalline powders offers a unique advantage for the production of adherent films with controlled microstructures on dense or porous substrates at relatively low temperatures.