Phase Transformations of Lithium Nitride under Pressure

Abstract

The transformation of α-Li3N to β-Li3N occurs at 600 MPa and room temperature. The reverse transformation, however, only begins to take place above 200°C under normal pressure. β-Li3N crystallizes as the Na3As structure type. This modification allows Li3N to be placed systematically in the structural series of alkali-metal compounds A3B 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-Li3N upon grinding with a mortar and pestle cannot be ruled out. Indeed, X-ray powder diffractions of α-Li3N always reveal the presence of small amounts of β-Li3N

Elastic Properties of <i>&alpha;</i>- and <i>&beta;</i>-phases of Li₃N

“…The optimized structural parameters, bulk modulus and its pressure derivative are given in Table 1, along with other theoretical results and available experimental measurements. It is seen that the calculated lattice parameters are better in the present study and agree well with experiments [8]. c/c 0 a/a 0 By fitting these data to third order polynomials of pressure, we obtain the following relationships at T = 0:…”

“…The equation of state EOS of the D 6h 4 phase has been measured up to 35 GPa [11]. The experimental P-V n data points 8 are plotted in the same figure which shows nice agreement with our ab initio calculation.…”

“…The density ρ has been assumed to be pressure dependent while calculating pressure dependent quantities mentioned above in Eqs. (2)(3)(4)(5)(6)(7)(8). The value of Θ D = 755 K for α-Li 3 N at P = 0 may be compared to 1016K for MgB 2 [33] and 743K for TiB 2 [34].…”

“…This layered structure consists of Li 2 N layers, widely separated by a pure Li layer which occupies a site between the nitrogen atoms in adjacent layers [1,7]. In the Li 2 (space group P6/mmm) [8].…”

Na3N—An Original Synthetic Route for a Long Sought After Binary Nitride

“…This arrangement results in a low space filling and thus, it is not surprising, that two high-pressure polymorphs were described to date. [14] The previous reports on the binary nitrides of the heavier alkali metals, on the other hand, seem doubtful. First hints of the formation of K 3 N from the thermal decomposition of KNH 2 date back to the classical work on the isolation of alkali metals by Davy as well as Gay-Lussac and The ¬ nard, performed at the beginning of the 19th Century.…”