Complex 5d Magnetism in a Novel S = 1/2 Trimer System, the 12L Hexagonal Perovskite Ba4BiIr3O12

详细信息    查看全文

• 作者：Wojciech Miiller ; Matthew T. Dunstan ; Zixin Huang ; Zakiah Mohamed ; Brendan J. Kennedy ; Maxim Avdeev ; Chris D. Ling
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：November 4, 2013
• 年：2013
• 卷：52
• 期：21
• 页码：12461-12467
• 全文大小：340K
• 年卷期：v.52,no.21(November 4, 2013)
• ISSN：1520-510X

文摘

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* 鈮?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.