Routes to the Quaternary Aluminum Silicides RE4Fe2+xAl7-xSi8 (RE = Ce, Pr, Nd, Sm); Exploratory Synthesis with Molten Al as a Solvent

Abstract

The four new intermetallic aluminum silicides RE4Fe2+xAl7-xSi8 (RE = Ce, Pr, Nd, Sm) crystallize from the reaction of Si, Fe, and RE (or rare earth oxides) in molten Al at 850 °C. All compounds share the same structure type as determined by single-crystal X-ray diffraction analysis. They form in the space group Cmmm (No. 65) with cell constants of a = 10.909(2) A, b = 16.265(3) A, c = 4.0804(8) A, R1 = 0.0196, and wR2 = 0.0486 for the Sm analogue. The crystal structure is a complex three-dimensional network comprised of repeating layers containing Al, Si, and Fe connected by atoms between the layers. The RE3+ ions are then located within tunnels of the three-dimensional network, running parallel to the c axis with a coordination number of 14. Magnetic susceptibility measurements indicate that the rare earth ions are in a 3+ oxidation state, whereas the Fe atoms are in an effective diamagnetic state. Electronic band structure calculations, carried out on the hypothetical analogue Y4Fe2Al7Si8, predict metal...