Lithium nitride


Lithium nitride is a compound with the formula Li3N. It is the only stable alkali metal nitride. The solid is a reddish-pink color and has a high melting point.

Preparation and handling

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

Structure and properties

alpha-Li3N 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. Two other forms are known: beta-Lithium nitride, formed from the alpha phase at has the sodium arsenide structure; gamma-Lithium nitride forms from the beta form at.
Lithium nitride shows ionic conductivity for Li+, with a value of c. 2×10−4Ω−1cm−1, and an activation energy of c. 0.26eV. Hydrogen doping increases conductivity, whilst doping with metal ions reduces it. The activation energy for lithium transfer across lithium nitride crystals has been determined to be higher at c. 68.5 kJ/mol. The alpha form is a semiconductor with band gap of c. 2.1 eV.
Reaction with hydrogen at under 300 °C produces lithium hydride and lithium amide.
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.
Reacting lithium nitride with carbon dioxide results in amorphous carbon nitride, a semiconductor, and lithium cyanamide, a precursor to fertilizers, in an exothermic reaction.