The ternary system Gd–Ge–Sn at 600 0C

Abstract

The isothermal section at 6000C of the phase diagram of the ternary system Gd–Ge–Sn was constructed in the whole concentration range, based on X-ray powder diffraction and energy-dispersive X-ray spectroscopy. The formation of two continuous solid solutions, Gd5Ge4–xSnx (x=0–4, structure type Sm5Ge4, Pearson symbol oP36, space group Pnma, a=7.8565(12)–8.040(2), b=14.812(2)–15.552(3), c=7.7781(12)–8.201(2) Å) and Gd5Ge3–xSnx (x=0–3, structure type Mn5Si3, hP16, P63/mcm, a=8.5702(8)–9.0306(13), c=6.4305(5)–6.5941(10) Å), and limited solid solutions based on the binary compounds Gd11Ge10 (6 at.% Sn), GdSn3 (5.5 at.% Ge), Gd3Sn7 (2 at.% Ge), GdSn2 (5 at.% Ge), and Gd11Sn10 (3.5 at.% Ge) was established. Three following ternary compounds were found in the system at 6000C: Gd2Ge3.84Sn0.92, GdGe0.75–0.85Sn1.25–1.15, and Gd2Ge2.91Sn0.80. The detailed crystal structures of two of them were refined on X-ray powder diffraction data: GdGe0.75–0.85Sn1.25–1.15, structure type ScCo0.25Si1.75, oS12, Cmcm, a=4.3206(4)–4.3035(4), b=16.4824(15)–16.4433(14), c=4.1270(4)–4.0961(4) Å and Gd2Ge2.91Sn0.80, structure type Gd2Ge3.38Bi0.42, oS32, Cmcm, a=4.0445(6), b=30.473(5), c=4.1694(6) Å. The third compound, Gd2Ge3.84Sn0.92, adopts the structure type Nd2Ge3.55Sn1.24. The crystal structures are closely related and are built from layers of Gd6 trigonal prisms centered by Ge atoms (or in part by Sn atoms) and square-mesh nets of Sn atoms (or in part Ge atoms), which alternate along the crystallographic direction [010]. Partial disorder of Ge and Sn atoms is observed.