The structural and magnetic characterization of 6H-perovskite-type oxides Ba₃LnIr₂O₉(Ln = Y, lanthanides)

Abstract

The crystal structures and magnetic properties of quaternary oxides Ba 3 LnIr 2 O 9 (Ln = Y, lanthanides) are reported. Rietveld analyses of their x-ray diffraction data indicate that they adopt the 6H-perovskite-type structure with space group P6 3 /mmc or, in the case of Ln = La and Nd only, a monoclinically distorted structure with space group C2/c. They have the valence state of Ba 3 Ln 4+ Ir 4+ 2 O 9 (for Ln = Ce, Pr, and Tb) or Ba 3 Ln 3+ Ir 4.5+2 O 9 (for Ln = Y and other lanthanides). Measurements of the magnetic susceptibility and specific heat were carried out for Ln = Y, Ce, Pr, Tb, and Lu. It was found that the effective magnetic moment of Ir ions is significantly small, which indicates the existence of the strong antiferromagnetic interaction between Ir ions in the Ir 2 O 9 bioctahedra. The Y and Lu compounds with an unpaired magnetic moment remaining in the Ir 4.5+2 O 9 show an antiferromagnetic transition at 4.0 and 5.1 K, respectively. For Ba 3 TbIr 2 O 9 , a long-range magnetic ordering of Tb 4+ ions was found at 2.0 K.

Possible spin-orbit driven spin-liquid ground state in the double perovskite phase of Ba3YIr2O9

“…Our XRD analysis confirmed that the AP sample was formed in a hexagonal structure (P6 3 /mmc) as reported earlier 10 but we found that after high-pressure treatment the structure changed to a cubic double perovskite (Ba 2 MM'O 6 ) phase with space group Fm-3m. It is relevant to mention that Ba 3 NiSb 2 O 9 was also reported to transform from a hexagonal (P6 3 /mmc) to cubic (Fm-3m) phase when treated under 9 GPa pressure at 1273 K for 30 min.…”

“…Ba 3 YIr 2 O 9 has a similar chemical formula like Ba 3 IrTi 2 O 9 and it crystallizes in the hexagonal structure (P6 3 /mmc) with Ir-Ir structural dimers arranged in an edge-shared triangular fashion. 10 Since all the Ir are equivalent, they should have a fractional oxidation state of +4.5 in a simple ionic picture. Our investigation of this 5d-based system is motivated by the fact that the fractional valence coupled with a geometrically frustrated lattice might lead to a spin-liquid state or possibly a heavy fermion state as in the 3d-based LiV 2 O 4 .…”

“…[13][14][15] We have prepared a polycrystalline sample of Ba 3 YIr 2 O 9 by the solid-state reaction method as detailed in Ref. 10. Further, the ambient pressure (AP) sample was treated under 8 GPa pressure at 1273 K for 30 min to get the HP sample.…”

“…For the AP sample, magnetic susceptibility shows a kink at T ∼ 4 K indicative of magnetic ordering as reported earlier. 10 Susceptibility data of the AP sample could be fitted to the Curie law (with θ ∼ 0) in the temperature range 30-300 K, which yields a T -independent susceptibility χ 0 = 3.8 × 10 −4 cm 3 /mol Ir and a Curie constant C = 0.0125 cm 3 K/mol Ir. The small Curie term (nearly thirty times smaller than that for S = 1/2) is not unusual in iridates.…”

Synthesis and magnetic properties of 12L-perovskites Ba4LnIr3O12 (Ln=lanthanides)

“…Impurity phases such as 6L-perovskite Ba 3 LnIr 2 O 9 [25,26] were formed due to the sublimation of Ba oxides and Ir oxides. In order to decrease such impurity phases, the excess amount (~ 30 %) of BaIrO 3 [32,33] was added during sample preparation.…”