PHASE EQUILIBRIA IN A Sn–As–P SYSTEM WITH A TIN CONCENTRATION LESS THAN 50 MOL. %

Abstract

In a Sn–As–P ternary system there is a continuous row of solid solutions (Sn4Р3)х(Sn4As3)1–х (α-solid solution), as well as broad areas of solid solubility based on tin monoarsenid (β solid solutions) and SnP3 phosphide (γ solid solutions). However, the nature of phase equilibria in the fi eld with the contents of the tin less than 50 mol. % has barely been researched. In the present work, based on the study of polythermal cross-section SnAs-SnP3 and a number of alloys with lower tin content the phase equilibria scheme in the Sn–As–P system is proposed. The results of XRD alloy cuts revealed that specimens with up to 30 mol. % of tin phosphide are homogeneous. This indicates the formation of a solid solution in the substitution of atoms of arsenic in the SnAs lattice by phosphorus. With the increased content of SnP3 the alloys are heterogeneous, and the lines of γ and α solid solutions with in addition to the β solid solution are fi xed. For samples with less content of tin the XRD data demonstrated the presence in addition to β and γ solid solutions of another phase – As1–xPx. According to differential thermal analysis, liquidus surface temperature decreases with increasing molar percentage of tin in alloy. These data suggest the existence of two invariant equilibria in the fi eld phase diagram Sn–As–P with tin content less than 50 mol. %. At 820 K exists (L) ↔ α + β + γ and at 824 K peritectic equilibria is implemented with the participation of solid solutions on the basis of tin monoarsenid and SnP3 phosphide staging δ-phase As1–xPx: L + δ ↔ β + γ.

Keywords

• phase diagram
• tin phosphides
• tin arsenides
• solid solution.