Metastable phases synthesized by inert-gas-condensation

Abstract

Using the inert-gas condensation method we have produced metastable phases of Ta, W and Y 2O 3. The formation of these phases results from both the undercooling achieved during inert-gas condensation as well as the surface-tension-induced increase in pressure with decreasing particle size. For example, we have found that Y 2O 3 can be synthesized in the equilibrium cubic phase (α-Y 2O 3) as well as in the high-pressure monoclinic phase (γ-Y 2O 3) by varying the preparation conditions. The resulting crystal structure is found to be determined by the crystallite size 〈D〉. Based on these observations it is shown that by utilizing-inert gas condensation one can prepare metastable structures and alloys that can hardly be synthesized by classical metallurgical processes.