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



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


The synthesis, structure, and elementary magnetic and electronic properties are reported for layered compounds of the type Na3-xMIr2O6 and Na3-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 Na1-xM{1/3}Ird{2/3}O2 or Na{1-x}Md{2/3}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 Na0.61Mn0.63Ir0.37O2, Na0.80Fe{2/3}Ir{1/3}O2, Na0.92Ni{1/3}Ir{2/3}O2, Na{0.86}Cu{1/3}Ir{2/3}O2, and Na0.89Zn{1/3}Ir{2/3}O2 display dominant antiferromagnetic interactions. For Na0.90Co{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 Na0.92Ni{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 Na0.92Ni{1/3}Ir{2/3}Od2^ and Na0.89Zn{1/3}Ir{2/3}Od2^ provide strong indications that the electron spins are short-range ordered in the latter two materials. Na0.61Mn0.63Ir0.37O2, Na0.80Fe{2/3}Ir{1/3}O2, Na0.90Co{1/3}Ir{2/3}O2, Na0.92Ni{1/3}Ir{2/3}O2, Na0.86Cu{1/3}Ir{2/3}O2 and Na0.89Zn{1/3}Ir{2/3}O2 are spin glasses.
Journal of Solid State Chemistry


Sodium Iridates, Structure, Magnetic property, Neutron diffraction


Baroudi, K. , Yim, C. , Wu, H. , Huang, Q. , , J. , Vavilova, E. , Grafe, H. , Kataev, V. , Buechner, B. , Ji, H. , Kuo, C. , Hu, Z. , Pi, T. , Pao, C. , Lee, J. , Mikhailova, D. , , L. and , R. (2014), Structure and Properties of &#945;-NaFeO<sub>2</sub>-type Ternary Sodium Iridates, Journal of Solid State Chemistry, [online], (Accessed June 18, 2021)
Created February 1, 2014, Updated February 19, 2017