Silver delafossite nitride, AgTaN2?

A new silver nitride, AgTaN2, was synthesized from NaTaN2 by a cation-exchange reaction, using a AgNO3–NH4NO3 flux at 175 °C. Its crystal structure type is delafossite (R3¯m) with hexagonal lattice parameters of a=3.141(3) Å, c=18.81(2) Å, in which silver is linearly coordinated to nitrogen. Energy dispersive X-ray analysis and combustion nitrogen/oxygen analysis gave a composition with atomic ratios of Ag:Ta:N:O as 1.0:1.2(1):2.1(1):0.77(4), which is somewhat Ta rich and indicates some oxide formation. The X-ray photoelectron spectroscopy analysis showed a Ta- and O-rich surface and transmission electron microscope observation exhibited aggregates of ca. 4–5 nm-sized particles on the surface, which are probably related to the composition deviation from a AgTaN2. The lattice parameters of stoichiometric AgTaN2 calculated by density functional theory agree with the experimental ones, but the possibility of some oxygen incorporation and/or silver deficiency is not precluded.