Ternary Rare-Earth Iron Arsenides RE12Fe57.5As41 (RE = La, Ce).

The rare-earth iron arsenides RE12Fe57.5As41 (RE = La, Ce) have been prepared by direct reactions of the elements in the presence of a Sn flux. Analysis of single-crystal X-ray diffraction data reveals that they adopt a new orthorhombic structure type (Pearson symbol oP236, space group Pmmn, Z = 2; a = 10.8881(9) Å, b = 25.753(2) Å, c = 12.5436(10) Å for RE = La; a = 10.8376(8) Å, b = 25.639(2) Å, c = 12.4701(9) Å for RE = Ce). In this metal-rich arsenide, the complex three-dimensional network (derived from 4 RE, 24 Fe, and 17 As sites) can be described as being built from unusual wavelike layers of connected As-centered trigonal prisms. Five of the Fe sites are partially occupied. The electronic structure of these compounds was probed through core-line X-ray photoelectron spectra. Magnetic susceptibility measurements indicated ferromagnetic ordering at TC = 125 and 95 K for the La and Ce compounds, respectively. Electrical resistivity measurements on single crystals of Ce12Fe57.5As41 showed metallic behavior with a prominent transition that coincides closely with the ferromagnetic ordering temperature. [ABSTRACT FROM AUTHOR]