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La 3 X 3 Z – Compounds with Condensed La 6 Z Octahedra Helically Connected in Three Dimensions
Author(s) -
Zheng Chong,
Oeckler Oliver,
Mattausch Hansjürgen,
Simon Arndt
Publication year - 2001
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/1521-3749(200109)627:9<2151::aid-zaac2151>3.0.co;2-0
Subject(s) - isostructural , octahedron , crystallography , materials science , metal , crystal structure , lattice constant , main group element , band gap , transition metal , chemistry , physics , metallurgy , biochemistry , optoelectronics , diffraction , optics , catalysis
The subhalides La 3 X 3 Z (X = Br, I, Z = Si, P, As, Sb, C 2 ) were synthesized from stoichiometric mixtures of La, LaX 3 and Z under Ar atmosphere in sealed Ta ampoules at 950 °C to 1200 °C for 3–30 days. La 3 X 3 Z (X = Br, I, Z = Si, P, As, Sb) is isostructural to Gd 3 Cl 3 C (Z = 8, space group I4 1 32, No. 214) which can be described as a defect NaCl type. This structure is characterized by the main group element Z centered octahedra propagating helically in three dimensions. The lattice constants a are 12.163(3), 12.4267(5), 12.533(1) and 12.780(1) Å for La 3 Br 3 Si, La 3 I 3 P, La 3 I 3 As and La 3 I 3 Sb, respectively. The excess electrons in the La d xy conduction band lead to a metallic behavior for these compounds. La 3 Br 3 Si undergoes a metal‐insulator transition at 36 K which is attributed to a structural change. La 3 Br 3 C 2 crystallizes in a different space group C222 1 (No. 20), Z = 16, a = 11.5330(6) Å, b = 17.0698(6) Å, c = 17.0540(8) Å. The C 2 units center highly distorted La octahedra. This structure, however, is related to the above I4 1 32 structure in that the edge‐sharing La 6 octahedra fill space in a similar way. This compound is a semiconductor (electrical gap E g = 0.02 eV) and its conducting property can be understood from the closed‐shell electron configuration of (La 3+ ) 3 (Br – ) 3 (C 2 ) 6– .