Properties and structure of AsTe glasses. (I). Glass-forming ability and related properties

TLDR: In this paper, a coherent analysis of all the data is developed which shows that important differences of local order exist between amorphous and crystalline states and also between the two well-distinct types of glasses we are dealing with.

Abstract: AsTe glasses have been investigated for determining the molecular mechanisms of glass formation and of crystallization. Stable and homogeneous bulk glasses are prepared throughout the range of concentration from 20 to 65 at % As, by using an improved quenching method. GFA (glass-forming ability) is determined with respect to the rate of cooling. Density, microhardness, T g and ΔC p at T g are measured in the whole range of glass formation. Finally a quantitative analysis of the kinetics of crystallization is carried out. It appears that most properties which involve molecular motions exhibit anomalies for As 40 Te 60 composition (As 2 Te 3 is the unique definite compound of the system). So GFA shows a sharp depression for this critical composition; similarly enthalpy and kinetics of crystallization are drastically modified at As 40 Te 60 . For Te-rich glasses, crystallization occurs at low temperature by homogeneous nucleation with a small energy of activation. For As-rich glasses, crystallization occurs at much higher temperatures. Above 200°C it is controlled by growth with an high activation energy which indicates deep rearrangements of the relative positions of the atoms by chemical diffusion. A coherent analysis of all the data is developed which shows that important differences of local order exist between amorphous and crystalline states and also between the two well-distinct types of glasses we are dealing with. The aim of paper II is to determine these differences from diffraction data.