In situ and ex situ investigation of the displacive phase transformations Ag3Sn(h) → Ag3Sn(l) and Ag3Sb(h) → Ag3Sb(l)

Abstract

Abstract The occurence of the polymorpic phase transformations Ag3Sn(h) → Ag3Sn(l) and Ag3Sb(h) → Ag3Sb(l) was demostrated in situ primarily by means of high-temperature X-ray powder diffracion and thermal analysis as well as by ex situ X-ray powder diffraction. Both solid- and liquid-quenched aloys were investigated. The structure of the high-temperature phases Ag3Sn(h) and Ag3Sb(h) is isotypic with Mg (Pearson symbol hP2, space group P63/mmc); unit cell parameters are: a = 2.9863(8) Å, c = 4.784(2) Å for Ag3Sn(h) and a = 2.9944(9) Å, c = 4.812(3) Å for Ag3Sb(h). The low temperature phases Ag3Sn(l) and Ag3Sb(l) are orthorhombic displacive homeotypes of the hexagonal close-packed structure, isotypic with with β-TiCu (oC4, Cmcm). The unit cell parameters are for Ag3Sn(l): a = 2.9973(5) Å, b = 5.1618(8) Å, c = 4.786(1) Å, b/a = 1.722 < √3; and for Ag3Sb(l): a = 2.9947(3) Å, b = 5.2497(5) Å, c = 4.8495(7) Å, b/a = 1.753 > √3. The crystal structures and the phase transformations werde discussed in terms of the valence electron concentration.