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potassium nitride; structure; powder diffraction; structure prediction; thermal properties
Abstract:
Two phases in the binary system K/N have been obtained via
co-deposition of potassium and nitrogen onto polished sapphire at 77 K
and subsequent heating to room temperature. The powder diffraction
pattern of one of these phases can be satisfactorily interpreted by
assuming the composition K3N, and the anti-TiI3 structure-type, which
is also adopted by Cs3O. The resulting hexagonal lattice constants are:
a = 779.8(2), c = 759.2(9) pm, Z = 2, P6(3)/mcm. Comparison with
possible structures Of K3N generated by computational methods and
refined at Hartree-Fock- and DFT level, reveals that the energetically
most favoured structure has not formed (presumable Li3P-tyPe), but
instead one of those with very low density. In this respect, the
findings for K3N are analogous to the results on Na3N. The thermal
evolution of the deposited starting mixture has been investigated.
Hexagonal K3N transforms to another K/N phase at 233 K. Its XRD can be
fully indexed resulting in an orthorhombic cell a = 1163, b = 596, c =
718 pm. Decomposition leaving elemental potassium as the only residue
occurs at 263 K.
