Vacancy Ordering in SmGe2-x and GdGe2-x (x = 0.33): Structure and Properties of Two Sm3Ge5 Polymorphs and of Gd3Ge5

Abstract

The crystal structures and the magnetic properties of three new binary rare-earth intermetallic phases are reported. alpha-Sm3Ge5 and beta-Sm3Ge5 and Gd3Ge5 have been prepared from the corresponding elements through high-temperature reactions using the flux-growth method. The structures of the three compounds have been established using single-crystal X-ray diffraction: alpha-Sm3Ge5 crystallizes with its own type in the hexagonal space group P2c (No. 190) with cell parameters a = 6.9238(11) A, c = 8.491(3) A, and Z = 2, whereas beta-Sm3Ge5 adopts the face-centered orthorhombic Y3Ge5 type with space group Fdd2 (No. 43) and with cell parameters a = 5.8281(6) A, b = 17.476(2) A, c = 13.785(2) A, and Z = 8. The orthorhombic Gd3Ge5 with cell parameters a = 5.784(2) A, b = 17.355(6) A, and c = 13.785(5) A is isostructural with beta-Sm3Ge5. The structures of the title compounds can be described as AlB(2) and alpha-ThSi2 derivatives with long-range ordering of the germanium vacancies. Temperature-dependent DC magnetization (5-300 K) measurements show evidence of antiferromagnetic ordering below ca. 30 and 10 K for alpha-Sm3Ge5 and beta-Sm3Ge5, respectively. Gd3Ge5 undergoes two successive magnetic transitions below ca. 15 and 11 K. The temperature dependence of the resistivity and heat capacity of Gd3Ge5 are discussed as well.