The coloring problem in intermetallics: bonding and properties of Tb3Zn3.6Al7.4 with the La3Al11 structure type

Single crystals of the new compound Tb3Zn3.6(1)Al7.4(1) were obtained from Al and Zn-rich ternary solutions. The title compound crystallizes in the orthorhombic La3Al11 structure type (space group Immm (No. 71), Z = 2; a = 4.2334(1) Aa, b = 9.9725(3) Aa, c = 12.4659(1) Aa). The inverse susceptibility above ca. 50 K shows Curie-Weiss behavior, and a metamagnetic transition is apparent in the T = 2 K field-dependent magnetization around Hc ∼ 20 kG. The resistivity increases with temperature in a roughly linear fashion, indicating the metallic character of this material. TB-LMTO-ASA electronic structure calculations indicate that this new intermetallic phase has all bonding states optimized in the [Zn4-xAl7+x] network, which classifies this compound among the so-called ''polar intermetallics.'' The calculations also provide a rationalization of the nonrandom ordering of Zn and Al atoms, which can be attributed to optimizing ((Zn, Al)-Zn, Al) orbital interactions. (orig.)