Abstract
The Sn-Se eutectic solidification allows one to obtain a lamellar structure, formed by SnSe and SnSe2 compounds, which are p and n semiconducting types, respectively. The SnSe-SnSe2 eutectic composite is a promising material to be used in photovoltaic device manufacturing. In a lamellar eutectic microstructure, the main parameter, which governs many of its characteristics, is the lamellar spacing. Such a parameter is primarily a result of the undercooling at the solid/liquid interface, which depends on the growth rate and the eutectic system properties. In this work, the Sn-Se alloy corresponding to eutectic composition was studied by using DSC thermal analysis and directional solidification at several growth rates in a vertical Bridgman-Stockbarger unit. The objective of the experiments was to investigate the influence of the growth rate on the growth undercooling, as well as on the eutectic microstructure. The microstructure analysis showed that a very regular and aligned structure formed by the SnSe and SnSe2 solid phases can be produced. By using the classic eutectic growth theory developed by Jackson and Hunt, the experimental results obtained led to the evaluation of a relationship among growth rates, eutectic growth temperature and lamellar spacing.
Highlights
In recent decades, eutectic alloy growth has been the subject of several theoretical and experimental studies[1,2,3,4]
The reason for performing the thermal analysis of the Sn-Se eutectic alloy was connected to the evaluation of the equilibrium temperature of the transformation liquid → SnSe+SnSe2 as a significant discrepancy is verified among the results obtained by several authors[16]
In order to eliminate the evident inconsistencies in these earlier investigations, the eutectic equilibrium temperature was determined during the heating cycle of the thermal analysis, as in the cooling cycle the eutectic temperature is a function of the growth rate[17,18,19,20]
Summary
Eutectic alloy growth has been the subject of several theoretical and experimental studies[1,2,3,4]. If a eutectic alloy is directionally grown, a regular structure consisting of two solid phases can be formed: the α and β phases. This phenomenon is a result of a cooperative growth of an oriented and an anisotropic structure, where both solid phases grow side by side. While the α phase segregates the component B, the β phase rejects the component A This process results in a solute increase in the liquid ahead of the α and β phases and to lateral mass transport due to the composition gradients of A and B. Lateral mass transport is fundamental to the eutectic growth process
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