Composition requirements for glass formation in metallic and ionic systems

WE have developed in recent papers the point of view that all liquids, ionic and metallic included, would form glasses when sufficiently undercooled, save for the intervention of crystallization^1-3. We have shown ² that the glass-forming tendency (for a given rate of cooling and for substances of a given molecular type) is greater the lower is the reduced melting temperature : where T_m is the thermodynamic crystallization temperature, and h_v is the molecular heat of vaporization. This criterion is in semi-quantitative accord with experience on glass formation. In particular it encompasses Zachariasen's⁴ criterion, and accounts for the enhancement of glass-forming tendency by molecular asymmetrization, both being simply equivalent to the depression of τ_m. It is also clear, as we pointed out, that the addition of impurities which depress τ_m similarly enhances the glass-forming tendency. In this communication we point out striking new experimental confirmation of this last deduction.