Structure and Properties of α-NaFeO2-type Ternary Sodium Iridates

Published

February 1, 2014

Author(s)

Kristen Baroudi, Cindi Yim, Hui Wu, Qingzhen Huang, John H. Roudebush, Eugenia Vavilova, Hans-Joachim Grafe, Vladislav Kataev, Bernd Buechner, Huiwen Ji, Changyang Kuo, Zhiwei Hu, Tun-Wen Pi, Chiwen Pao, Jyhfu Lee, Daria Mikhailova, Liu Hao Tjeng, R. J. Cava

Abstract

The synthesis, structure, and elementary magnetic and electronic properties are reported for layered compounds of the type Na_3-xMIr₂O₆ and Na_3-xM₂IrO₆, where M is a transition metal from the 3d series (M=Zn, Cu, Ni, Co, Fe and Mn). The rhombohedral structures, in space group R-3m, were determined by refinement of neutron and synchrotron powder diffraction data. No clear evidence for long range 2:1 or 1:2 honeycomb-like M/Ir ordering was found in the neutron powder diffraction patterns except in the case of M = Zn, and thus in general the compounds are best designated as sodium deficient α-NaFeO₂-type phases with formulas Na_1-xM_1/3}Ird2/3}O₂ or Na_1-x}Md2/3}Ir_1/3}Od2^. Synchrotron powder diffraction patterns indicate that several of the compounds likely have honeycomb in-plane metal-iridium ordering with disordered stacking of the layers. All the compounds are sodium deficient under our synthetic conditions and are black and insulating. Weiss constants derived from magnetic susceptibility measurements indicate that Na_0.61Mn_0.63Ir_0.37O₂, Na_0.80Fe_2/3}Ir_1/3}O₂, Na_0.92Ni_1/3}Ir_2/3}O₂, Na_0.86}Cu_1/3}Ir_2/3}O₂, and Na_0.89Zn_1/3}Ir_2/3}O₂ display dominant antiferromagnetic interactions. For Na_0.90Co_1/3}Ir_2/3}O₂ the dominant magnetic interactions at low temperature are ferromagnetic while at high temperatures they are antiferromagnetic; there is also a change in the effective moment. Low temperature specific heat measurements (to 2 K) on Na_0.92Ni_1/3}Ir_2/3}O₂ indicate the presence of a broad magnetic ordering transition. X-ray absorption spectroscopy shows that iridium is at or close to the 4+ oxidation state in all compounds. ²³Na nuclear magnetic resonance measurements comparing Na₂IrO₃ to Na_0.92Ni_1/3}Ir_2/3}Od2^ and Na_0.89Zn_1/3}Ir_2/3}Od2^ provide strong indications that the electron spins are short-range ordered in the latter two materials. Na_0.61Mn_0.63Ir_0.37O₂, Na_0.80Fe_2/3}Ir_1/3}O₂, Na_0.90Co_1/3}Ir_2/3}O₂, Na_0.92Ni_1/3}Ir_2/3}O₂, Na_0.86Cu_1/3}Ir_2/3}O₂ and Na_0.89Zn_1/3}Ir_2/3}O₂ are spin glasses.

Citation

Journal of Solid State Chemistry

Volume

210

Pub Type

Journals

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Keywords

Sodium Iridates, Structure, Magnetic property, Neutron diffraction

Citation

Baroudi, K. , Yim, C. , Wu, H. , Huang, Q. , Roudebush, J. , Vavilova, E. , Grafe, H. , Kataev, V. , Buechner, B. , Ji, H. , Kuo, C. , Hu, Z. , Pi, T. , Pao, C. , Lee, J. , Mikhailova, D. , Tjeng, L. and Cava, R. (2014), Structure and Properties of α-NaFeO₂-type Ternary Sodium Iridates, Journal of Solid State Chemistry, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=914673 (Accessed October 24, 2025)