Hydrogenation of the Ce(Rh1-xIrx)Ga System: Occurrence of Antiferromagnetic Ordering in the Hydrides Ce(Rh1-xIrx)GaH1.8

Abstract

The ternary gallides Ce(Rh1-xIrx)Ga with x = 0, 0.54, and 1 were synthesized from the elements by arc-melting. The structures of these intermediate valence compounds were investigated on the basis of powder and single-crystal X-ray diffractometer data: TiNiSi type, Pnma, a = 688.2(2), b = 439.6(1), and c = 788.9(1) pm, wR2 = 0.0493, 563 F2 values, and 20 variable parameters for CeRhGa; a = 685.5(1), b = 436.0(1), and c = 782.7(1) pm, wR2 = 0.0685, 563 F2 values, and 21 variable parameters for Ce(Rh0.46Ir0.54)Ga; and a = 690.1(1), b = 436.6(1) and c = 785.2(2) pm, wR2 = 0.0810, 562 F2 values, and 20 variable parameters for CeIrGa. The rhodium (or iridium) and gallium atoms build up three-dimensional [RhGa] and [IrGa] networks with Rh−Ga (or Ir−Ga) distances ranging from 265 to 267 pm (or from 265 to 269 pm). The cerium atoms fill distorted hexagonal channels within these networks with one short Ce−Rh (or Ce−Ir) contact (281 pm in CeRhGa, 283 pm in Ce(Rh0.46Ir0.54)Ga, and 287 pm in CeIrGa). Hydrogenation leads to the formation of the hydrides Ce(Rh1-xIrx)GaH1.8 in going with a switch in structure type: ZrBeSi type, P63/mmc, a = 437.3(1) and c = 839.2(1) pm for CeRhGaH1.8, a = 440.1(1) and c = 829.1(1) pm for Ce(Rh0.46Ir0.54)GaH1.8, and a = 441.8(1) and c = 823.3(1) pm for CeIrGaH1.8. Susceptibility and specific heat measurements on the hydrides reveal stable trivalent cerium and antiferromagnetic ordering at low temperatures; the Néel temperature decreases with the rhodium content. Fitting of the susceptibility data of the hydrides considering the crystal field splitting and molecular field effects clearly revealed the doublet Γ9 =| ±3/2 as the ground state. Electrical resistivity data and thermoelectric power measurements show the characteristics of Kondo systems.