Lithium iridate, Li₂IrO₃, is a chemical compound of

lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

iridium Iridium is a chemical element; it has the symbol Ir and atomic number 77. This very hard, brittle, silvery-white transition metal of the platinum group, is considered the second-densest naturally occurring metal (after osmium) with a density ...

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 Electrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity in ...

, and changes its magnetic ordering from

paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...

antiferromagnetic In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring Spin (physics), spins (on different sublattices) pointing in oppos ...

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.

Synthesis

Li₂IrO₃ crystals can be grown by direct

sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing process used with metals, ceramics, plas ...

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 Lithium carbonate is an inorganic compound, the lithium salt of carbonic acid with the chemical formula, formula . This white Salt (chemistry), salt is widely used in processing metal oxides. It is on the WHO Model List of Essential Medicines, Wor ...

, 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(IV) oxide, followed by annealing in molten

lithium hydroxide Lithium hydroxide is an inorganic compound with the formula LiOH. It can exist as anhydrous or hydrated, and both forms are white hygroscopic solids. They are soluble in water and slightly soluble in ethanol. Both are available commercially. While ...

at 700–800 °C.

Properties

Lithium iridate is black in color and has a relatively high, temperature-independent electrical conductivity characteristic of metals. 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 In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Curie ...

, ''T''_N), while the material is paramagnetic above ''T''_N.

Potential applications

Lithium iridate is a potential electrode material for the

lithium-ion battery A lithium-ion or Li-ion battery is a type of rechargeable battery that uses the reversible intercalation of Li+ ions into electronically conducting solids to store energy. Li-ion batteries are characterized by higher specific energy, energ ...

. This application is hindered by the high costs of Ir, as compared to the cheaper Li₂MnO₃ alternative.

References

{{Iridium compounds Lithium compounds Iridium compounds Transition metal oxyanions