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

Abstract

The ternary aluminides R 2 Rh 3 Al 9 ( R =Y, La–Nd, Sm, Gd–Tm, Lu), R 2 Ir 3 Al 9 ( R =Y, La–Nd, Sm, Gd–Lu), and R 2 Pd 3 Al 9 ( 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 Y 2 Co 3 Ga 9 -type structure: Cmcm , Z =4. The crystal structures of Ho 2 Rh 3 Al 9 and Er 2 Ir 3 Al 9 have been refined from single-crystal X-ray data; Ho 2 Rh 3 Al 9 : 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; Er 2 Ir 3 Al 9 : 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 = R 2 Al 3 and B = T 3 Al 6 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 Ho 2 Rh 3 Al 9 and Er 2 Ir 3 Al 9 , 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.