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Title: Complex 5d Magnetism in a Novel S = 1/2 Trimer System, the 12L Hexagonal Perovskite Ba4BiIr3O12
Authors: Miiller, W
Dunstan, MT
Huang, Z
Mohamed, Z
Kennedy, BJ
Avdeev, M
Ling, CD
Keywords: BARIUM
BISMUTH
LAWRENCIUM
PEROVSKITE
NEUTRON DIFFRACTION
RARE EARTHS
Issue Date: 4-Nov-2013
Publisher: American Chemical Society
Citation: Miiller, W., Dunstan, M.T., Huang, Z.X., Mohamed, Z., Kennedy, B.J., Avdeev, M., & Ling, C.D. (2013). Complex 5d magnetism in a novel s=1/2 trimer system, the 12l hexagonal perovskite ba4biir3o12. Inorganic Chemistry, 52(21), 12461-12467.
Abstract: The 12L hexagonal perovskite Ba4BiIr3O12 has been synthesized for the first time and characterized using high-resolution neutron and synchrotron X-ray diffraction as well as physical properties measurements. The structure contains Ir3O12 linear face-sharing octahedral trimer units, bridged by corner-sharing BiO6 octahedra. The average electronic configurations of Ir and Bi are shown to be +4(d5) and +4(s1), respectively, the same as for the S = 1/2 dimer system Ba3BiIr2O9, which undergoes a spin-gap opening with a strong magnetoelastic effect at T* = 74 K. Anomalies in magnetic susceptibility, heat capacity, electrical resistivity, and unit cell parameters indeed reveal an analogous effect at T* ≈ 215 K in Ba4BiIr3O12. However, the transition is not accompanied by the opening of a gap in spin excitation spectrum, because antiferromagnetic coupling among S = 1/2 Ir4+ (d5) cations leads to the formation of a S = 1/2 doublet within the trimers, vs S = 0 singlets within dimers. The change in magnetic state of the trimers at T* leads to a structural distortion, the energy of which is overcompensated for by the formation of S = 1/2 doublets. Extending this insight to the dimer system Ba3BiIr2O9 sheds new light on the more pronounced low-temperature anomalies observed for that compound. © 2013, American Chemical Society.
URI: http://dx.doi.org/10.1021/ic4014619
http://apo.ansto.gov.au/dspace/handle/10238/5862
ISSN: 0020-1669
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