KBi2-xPbx (0 < x ≤ 1): A zintl phase evolving from a distortion of the cubic laves-phase structure

Siméon Ponou, Noémi Müller, Thomas F. Fässler, Ulrich Häussermann

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Abstract

The quasibinary system KBi2-xPbx has been investigated, both experimentally and theoretically. Phases with compositions 0 ≤ x ≤ 1.2 were synthesized and structurally characterized by X-ray diffraction experiments. For low values of x (0 ≤ x < 0.6), KBi 2-xPbx adopts the cubic Laves-phase structure MgCu 2 (space group Fd3m), which contains a rigid framework of corner-condensed symmetry-equivalent tetrahedra formed by randomly distributed Bi and Pb atoms. For compositions x ≥ 0.6, these tetrahedra become alternately elongated and contracted. The distortion of the framework lowers the space-group symmetry to F43m (KBi1.2Pb0.8, F43m, Z = 8, a = 9.572(1) Å). Magnetometer measurements show that KBi2 (x = 0) is metallic and goes through a superconducting transition below 3.5 K. First principles calculations reveal that the Fd3m → F43m distortion is largest for KBiPb (x = 1.0), which at the same time turns into a semiconductor. Thus, F43m KBiPb corresponds to a proper charge-balanced Zintl phase, K +[BiPb]-, with separated polyanionic tetrahedra, (Bi 2Pb2)2-. However, it was not possible to prepare F43m KBiPb. Syntheses attempting to increase the Pb content in KBi 2-xPbx above x = 0.8 yielded additional, not yet characterized, ternary phases.

Original languageEnglish
Pages (from-to)7423-7430
Number of pages8
JournalInorganic Chemistry
Volume44
Issue number21
DOIs
StatePublished - 17 Oct 2005

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