Preparation and crystal structure of ternary rare-earth platinum metal aluminides R2T3Al9 (T= Rh, Ir, Pd) with Y2Co3Ga9-type structure and magnetic properties of the iridium compounds

摘要

The ternary aluminides R2Rh3Al9 (R = Y, La-Nd, Sm, Gd-Tm, Lu), R2Ir3Al9 (R = Y, La-Nd, Sm, Gd-Lu), and R2Pd3Al9 (R = Y, Gd-Tm) have been prepared by arc melting of the elemental components with an excess of aluminum and dissolving the aluminum-rich matrix in hydrochloric acid. They crystallize with Y2Co3Ga9-type structure: Cmcm, Z = 4. The crystal structures of Ho2Rh3Al9 and Er2Ir3Al9 have been refined from single-crystal X-ray data; Ho2Rh3Al9: a = 1316.8(3) pm, b = 760.2(2) pm, c = 933.7(2) pm, R = 0.044 for 255 structure factors and 27 variables; Er2Ir3Al9: a = 1313.8(2) pm, b = 758.5(1) pm, c = 933.8(2) pm, R = 0.057 (392 F values, 27 variables). The structure may be viewed as consisting of atomic layers of the compositions A = R2Al3 and B = T3Al6 which alternate in the sequence ABAB along the z direction. Approximately 33% and 27% of the A layers were found to be misplaced in the crystals investigated for Ho2Rh3Al9 and Er2Ir3Al9, respectively. The magnetic properties of most iridium-containing compounds have been determined with a superconducting quantum interference device magnetometer. The yttrium and the lanthanum compounds show Pauli paramagnetism, others reflect the magnetic behavior of the rare-earth components. The magnetic ordering temperatures are all lower than 20 K. (C) 2004 Elsevier Inc. All rights reserved.