Preparation and crystal structure of ternary rare-earth platinum metal aluminides R2T3Al 9 ( T=Rh, Ir, Pd) with Y 2Co 3Ga 9-type structure and magnetic properties of the iridium compounds

Abstract

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