Phase Transformations of Lithium Nitride under Pressure

Abstract

The transformation of α‐Li 3 N to β‐Li 3 N occurs at 600 MPa and room temperature. The reverse transformation, however, only begins to take place above 200°C under normal pressure. β‐Li 3 N crystallizes as the Na 3 As structure type. This modification allows Li 3 N to be placed systematically in the structural series of alkali‐metal compounds A 3 B involving elements of the nitrogen group (A = Li, Na, K, Rb, Cs; B = N, P, As, Sb, Bi). Since the phase transition occurs at relatively low pressure, the formation of small amounts of β‐Li 3 N upon grinding with a mortar and pestle cannot be ruled out. Indeed, X‐ray powder diffractions of α‐Li 3 N always reveal the presence of small amounts of β‐Li 3 N.