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Article

Vacancy Ordering in SmGe₂_-_x and GdGe₂_-_x (x = 0.33): Structure and Properties of Two Sm₃Ge₅ Polymorphs and of Gd₃Ge₅

Supporting Info

Paul H. Tobash, Daniel Lins, and Svilen Bobev*

Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716

Namjung Hur, Joe D. Thompson, and John L. Sarrao

Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545

Inorg. Chem., 2006, 45 (18), pp 7286–7294

DOI: 10.1021/ic060913f

Publication Date (Web): July 28, 2006

Author to whom correspondence should be addressed. Phone: (302) 831-8720. Fax: (302) 831-6335. E-mail: sbobev@chem.udel.edu.

Abstract

The crystal structures and the magnetic properties of three new binary rare-earth intermetallic phases are reported. α-Sm₃Ge₅ and β-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: α-Sm₃Ge₅ crystallizes with its own type in the hexagonal space group P6̄2c (No. 190) with cell parameters a = 6.9238(11) Å, c = 8.491(3) Å, and Z = 2, whereas β-Sm₃Ge₅ adopts the face-centered orthorhombic Y₃Ge₅ type with space group Fdd2 (No. 43) and with cell parameters a = 5.8281(6) Å, b = 17.476(2) Å, c = 13.785(2) Å, and Z = 8. The orthorhombic Gd₃Ge₅ with cell parameters a = 5.784(2) Å, b = 17.355(6) Å, and c = 13.785(5) Å is isostructural with β-Sm₃Ge₅. The structures of the title compounds can be described as AlB₂ and α-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 α-Sm₃Ge₅ and β-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.