Structure-composition sensitivity in 'Metallic' Zintl phases: A study of Eu(Ga{sub 1-x}Tt{sub x}){sub 2} (Tt=Si, Ge, 0<=x<=1)

Journal Article · Tue Sep 15 00:00:00 EDT 2009 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.06.032· OSTI ID:21370574

You, Tae-Soo ^[1]; Jingtai, Zhao ^[2]; Poettgen, Rainer ^[3]; Schnelle, Walter; Burkhardt, Ulrich; Grin, Yuri ^[4]

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1. Department of Chemistry, Iowa State University, Ames, IA 50011 (United States)
2. Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China)
3. Institut fuer Anorganische und Analytische Chemie, Universitaet Muenster, Corrensstrasse 30, 48149 Muenster (Germany)
4. Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Strasse 40, 01187 Dresden (Germany)

Two isoelectronic series, Eu(Ga{sub 1-x}Tt{sub x}){sub 2} (Tt=Si, Ge, 0<=x<=1), have been synthesized and characterized by powder and single-crystal X-ray diffraction, physical property measurements, and electronic structure calculations. In Eu(Ga{sub 1-x}Si{sub x}){sub 2}, crystal structures vary from the KHg{sub 2}-type to the AlB{sub 2}-type, and, finally, the ThSi{sub 2}-type structure as x increases. The hexagonal AlB{sub 2}-type structure is identified for compositions 0.18(2)<=x<0.70(2) with Ga and Si atoms statistically distributed in the polyanionic 6{sup 3} nets. As smaller Si atoms replace Ga atoms while the number of valence electrons increases, the lattice parameters, unit cell volumes, and Ga-Si distances in this phase region decrease significantly. Although aspects of X-ray diffraction results suggest puckering of the 6{sup 3} nets for the Si-richest example of the AlB{sub 2}-type Eu(Ga{sub 1-x}Si{sub x}){sub 2}, the complete experimental evidence remains inconclusive. On the other hand, in Eu(Ga{sub 1-x}Ge{sub x}){sub 2}, six different structural types were observed as x varies. In addition to EuGa{sub 2} (KHg{sub 2}-type; space group Imma) and EuGe{sub 2} (own structure type, space group P3-barm1), the ternary phases studied show four different structures: the AlB{sub 2}-type for Ga-rich compositions; the YPtAs-type structure for EuGaGe; and two new structures, which are intergrowths of the YPtAs-type EuGaGe and EuGe{sub 2}, for Ge-rich compositions. These two Ge-rich phases include: (1) Eu(Ga{sub 0.45(2)}Ge{sub 0.55(2)}){sub 2} containing two YPtAs-type motifs of EuGaGe plus one EuGe{sub 2} motif; and (2) Eu(Ga{sub 0.40(2)}Ge{sub 0.60(2)}){sub 2} containing one YPtAs-type motif alternating with a split site at x=2/3 ,y=1/3 and z=0.4798(2) with ca. 50% site occupancy by Ga and Ge along the c-axis. Magnetic susceptibilities of three Eu(Ga{sub 1-x}Ge{sub x}){sub 2} compounds display Curie-Weiss behavior above ca. 100 K, and show effective magnetic moments indicative of divalent Eu with a 4f{sup 7} electronic configuration, consistent with. X-ray absorption spectra (XAS). Density of states (DOS) and crystal orbital Hamilton population (COHP) analyses, based on first principles electronic structure calculations, rationalize the observed homogeneity ranges of the AlB{sub 2}-type phases in both systems and the structural variations as a function of Tt content. - Abstract: A study of Eu(Ga{sub 1-x}Si{sub x}){sub 2} and Eu(Ga{sub 1-x}Ge{sub x}){sub 2} shows different compositional ranges for puckering of 6{sup 3} nets and, for the germanides, two new commensurately modulated superstructures. Display Omitted

• OSTI ID: 21370574
• Journal Information: Journal of Solid State Chemistry, Vol. 182, Issue 9; Other Information: DOI: 10.1016/j.jssc.2009.06.032; PII: S0022-4596(09)00292-8; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

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37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTROSCOPY
CRYSTALLOGRAPHY
ELECTRONIC STRUCTURE
EUROPIUM COMPOUNDS
GALLIUM COMPOUNDS
GERMANIDES
INTERMETALLIC COMPOUNDS
LATTICE PARAMETERS
MAGNETIC MOMENTS
MAGNETIC SUSCEPTIBILITY
MONOCRYSTALS
SENSITIVITY
SILICIDES
SPACE GROUPS
TETRAGONAL LATTICES
TRIGONAL LATTICES
X-RAY DIFFRACTION
X-RAY SPECTRA
X-RAY SPECTROSCOPY
ALLOYS
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTALS
DIFFRACTION
GERMANIUM COMPOUNDS
MAGNETIC PROPERTIES
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
SCATTERING
SILICON COMPOUNDS
SPECTRA
SPECTROSCOPY
SYMMETRY GROUPS