Lithium iridate

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Lithium iridate
ALi2IrO3.jpg
α-Li2IrO3 (scale bar 0.3 mm)[1]
BLi2IrO3.jpg
β-Li2IrO3 (scale bar 0.2 mm)[1]
ALi2IrO3 str1.png
ALi2IrO3 str2.png
Crystal structure of α-Li2IrO3 with Ir shown in yellow, Li in purple and O in red
Names
Preferred IUPAC name
Lithium iridate
Identifiers
Properties
Li2IrO3
Appearance Black crystals
Structure
Monoclinic, C2/m[2]
a = 5.1633(2) Å, b = 8.9294(3) Å, c = 5.1219(2) Å
α = 90°, β = 109.759(3)°, γ = 90°
4
Related compounds
Other anions
Lithium ruthenate, lithium platinate
Other cations
Sodium iridate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Lithium iridate, Li2IrO3, is a chemical compound of lithium, iridium and oxygen. It forms black crystals with three slightly different layered atomic structures, α, β, and sometimes γ. Lithium iridate exhibits metal-like, temperature-independent electrical conductivity, and changes its magnetic ordering from paramagnetic to antiferromagnetic upon cooling to 15 K.

Structure

Li2IrO3 typically crystallizes in the α or β phase, and a rare γ phase has been reported. The crystal structure of α-Li2IrO3 consists of an alternate stacking of hexagonal Li layers and honeycombs of edge-sharing IrO6 octahedra with Li in the center. The offset in adjacent layers results in a relatively low (monoclinic) crystal symmetry. Li2IrO3 crystals have abundant twinning defects where the ab crystal planes are rotated by 120° around the c axis.[1]

Synthesis

Synthesis of Li2IrO3 from Li and Ir metals, which are oxidized during heating. The spiral staircase-like growth chamber allows for nucleation of different crystals at different staircase steps.[1]
Time-temperature diagram of Li2IrO3 synthesis.[1]

Li2IrO3 crystals can be grown by direct sintering of Ir and Li metals, which both oxidize during heating in ambient atmosphere. The α phase is formed at 750–1050 °C, while heating to higher temperatures results in the β phase. The use of Li metal instead of more traditional lithium carbonate, which is easier to handle and store, results in larger crystals. The γ phase can be obtained by the calcination of lithium carbonate and iridium, followed by annealing in molten lithium hydroxide at 700–800 °C.[1]

Properties

Lithium iridate is black in color and has a relatively high, temperature-independent electrical conductivity characteristic of metals.[2] Its both α and β phases exhibit the Kitaev exchange coupling between magnetic spins originating from Ir4+ ions. These spins form an antiferromagnetic lattice at temperatures below 15 K (Néel temperature, TN), while the material is paramagnetic above TN.[1]

Potential applications

Lithium iridate is a potential electrode material for the lithium-ion battery.[2] This application is hindered by the high costs of Ir, as compared to the cheaper Li2MnO3 alternative.[3]

References

  1. ^ a b c d e f g Freund, F.; Williams, S. C.; Johnson, R. D.; Coldea, R.; Gegenwart, P.; Jesche, A. (2016). "Single crystal growth from separated educts and its application to lithium transition-metal oxides". Scientific Reports. 6: 35362. arXiv:1604.04551. Bibcode:2016NatSR...635362F. doi:10.1038/srep35362. PMC 5066249. PMID 27748402.
  2. ^ a b c O'Malley, Matthew J.; Verweij, Henk; Woodward, Patrick M. (2008). "Structure and properties of ordered Li2IrO3 and Li2PtO3". Journal of Solid State Chemistry. 181 (8): 1803. Bibcode:2008JSSCh.181.1803O. doi:10.1016/j.jssc.2008.04.005.
  3. ^ Yoshio, Masaki; Brodd, Ralph J.; Kozawa, Akiya (17 July 2010). Lithium-Ion Batteries: Science and Technologies. Springer Science & Business Media. p. 10. ISBN 978-0-387-34445-4.
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