Ternary rhombohedral Laves phases <i>RE</i> ₂Rh₃Ga (<i>RE</i> = Y, La–Nd, Sm, Gd–Er)

Abstract

Abstract: The ordered Laves phases RE 2 Rh 3 Ga ( RE =Y, La–Nd, Sm, Gd–Er) were synthesized by arc-melting of the elements and subsequent annealing. The samples were characterized by powder X-ray diffraction (XRD). They crystallize with the rhombohedral Mg 2 Ni 3 Si type structure, space group R 3̅ m . Three structures were refined from single crystal X-ray diffractometer data: a =557.1(1), c =1183.1(2), wR2=0.0591, 159 F 2 values, 10 variables for Y 2 Rh 3 Ga, a =562.5(2), c =1194.4(2) pm, wR 2=0.0519, 206 F 2 values, 11 variables for Ce 2 Rh 3 Ga and a =556.7(2), c =1184.1(3) pm, wR 2=0.0396, 176 F 2 values, 11 variables for Tb 2 Rh 3 Ga. The Rh 3 Ga tetrahedra are condensed via common corners and the large cavities left by the network are filled by the rare earth atoms. The RE 2 Rh 3 Ga Laves phases crystallize with a translationengleiche subgroup of the cubic RE Rh 2 Laves phases with MgCu 2 type. Magnetic susceptibility measurements reveal Pauli paramagnetism for Y 2 Rh 3 Ga and La 2 Rh 3 Ga. Ce 2 Rh 3 Ga shows intermediate cerium valence while all other RE 2 Rh 3 Ga phases are Curie–Weiss paramagnets which order magnetically at low temperatures. The 89 Y and 71 Ga solid state nuclear magnetic resonance (NMR) spectra of the diamagnetic representative Y 2 Rh 3 Ga show well-defined single resonances in agreement with an ordered bulk phase. In comparison to the binary Laves phase YRh 2 a strongly increased 89 Y resonance frequency is observed owing to a higher s -electron spin density at the 89 Y nuclei as proven by density of states (DOS) calculations.