Lithium nitride is an inorganic compound with the chemical formula Li3N. It is the only stable alkali metal nitride. It is a reddish-pink solid with a high melting point.

Preparation and handling

Lithium nitride is prepared by direct reaction 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 must be protected from moisture as it reacts violently with water to produce ammonia:

Structure and properties

Two other forms are known: Lithium nitride shows ionic conductivity for Li+, with a value of c. 2×10−4 Ω−1cm−1, and an (intracrystal) activation energy of c. 0.26 eV (c. 24 kJ/mol). Hydrogen doping increases conductivity, whilst doping with metal ions (Al, Cu, Mg) reduces it. The activation energy for lithium transfer across lithium nitride crystals (intercrystalline) 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.

Reactions

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. Under hydrogen at around 200°C, Li3N will react to form lithium amide. At higher temperatures it will react further to form ammonia and lithium hydride. Lithium imide can also be formed under certain conditions. Some research has explored this as a possible industrial process to produce ammonia since lithium hydride can be thermally decomposed back to lithium metal. 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.