Preparation of single-phase (Cr,Zn)(N,O) by double substitution of ZnO into CrN: evaluation of hardness

Solid-solution hardening by the addition of other elements is a known method for enhancing the hardness of transition-metal nitrides (TMNs) such as chromium nitride (CrN) and titanium nitride (TiN), of which structure are NaCl-type (B1). In this study, we attempted to synthesize a novel single-phase (Cr,Zn)(N,O) thin film by the solid-solution substitution of zinc oxide (ZnO), which adopts the same B1 structure under high pressure, into the CrN lattice. Cr–Zn–N–O thin films with various ZnO contents were deposited onto MgO substrates using pulsed laser deposition. Compositional analysis confirmed that the thin films consisted only of Cr, Zn, N, and O. X-ray diffraction patterns suggested the formation of single-phase B1-(Cr,Zn)(N,O) in the thin film. The hardness of the (Cr,Zn)(N,O) thin film reached 23 GPa, representing a 28% increase over that of a CrN thin film (18 GPa) deposited under identical conditions.