Bulk Synthesis and Superconductivity of Rock Salt-Type, Nitrogen-Rich, Zirconium-Deficient Nitrides, Zr_1–<i>x</i>N

Zirconium nitrides were derived from crystalline powders of layer-structured ZrNCl via ammonothermal dechlorination at various temperatures under flowing ammonia gas. Regardless of which polymorph of ZrNCl was employed as a starting material, the products of the ammonothermal dechlorination reactions were zirconium nitride powders with the rock salt structure. The size of the cubic lattice parameter was found to be dependent on the ammonia flow rate. Each of the synthesized zirconium nitrides is nonstoichiometric and nitrogen-rich (zirconium-deficient), Zr1–xN, and some exhibit superconductivity at subambient temperature. The superconducting transition temperature (Tc) of each of the nitrides scales linearly with the corresponding cubic unit cell volume (lattice parameter, a) and the N/Zr ratio. This paper represents the first report of a superconducting dome in bulk nitrogen-rich zirconium nitrides with a rock-salt-type structure; to date, a unique characteristic among superconducting rock salt phases.