Lithium nitride

Lithium nitride is prepared by direct combination of elemental lithium with nitrogen gas:[2]

6 Li + N₂ → 2 Li₃N

Instead of burning lithium metal in an atmosphere of nitrogen, a solution of lithium in liquid sodium metal can be treated with N₂. Lithium nitride reacts violently with water to produce ammonia:

Li₃N + 3 H₂O → 3 LiOH + NH₃

alpha-Li₃N (stable at room temperature and pressure) has an unusual crystal structure that consists of two types of layers, one sheet has the composition Li₂N⁻ contains 6-coordinate N centers and the other sheet consists only of lithium cations.[3] Two other forms are known: beta-Lithium nitride, formed from the alpha phase at 4,200 bars (4,100 atm) has the sodium arsenide (Na₃As) structure; gamma-Lithium nitride (same structure as Li₃Bi) forms from the beta form at 35 to 45 gigapascals (350,000 to 440,000 atm).[4]

Lithium nitride shows ionic conductivity for Li⁺, with a value of c. 2×10⁻⁴Ω⁻¹cm⁻¹, and an (intracrystal) activation energy of c. 0.26eV (c. 24 kJ/mol). Hydrogen doping increases conductivity, whilst doping with metal ions (Al, Cu, Mg) reduces it.[5][6] The activation energy for lithium transfer across lithium nitride crystals (intercrystalline) has been determined to be higher at c. 68.5 kJ/mol.[7] The alpha form is a semiconductor with band gap of c. 2.1 eV.[4]

Reaction with hydrogen at under 300 °C (0.5 MPa pressure) produces lithium hydride and lithium amide.[8]

Lithium nitride has been investigated as a storage medium for hydrogen gas, as the reaction is reversible at 270 °C. Up to 11.5% by weight absorption of hydrogen has been achieved.[9]

Reacting lithium nitride with carbon dioxide results in amorphous carbon nitride (C₃N₄), a semiconductor, and lithium cyanamide (Li₂CN₂), a precursor to fertilizers, in an exothermic reaction.[10] [11]

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