  Experimental manipulation of superconductivity is of paramount importance,
not only for practical applications but also for identifying the key factors
involved in electron pairing. In this work, we have undertaken a meticulous
study of the superconductivity in a series of titanium compounds with a
rocksalt structure, synthesized as epitaxial films. We find that substituting
nitrogen (N) for oxygen (O) in titanium monoxide (TiO) with the stoichiometry
close to TiO$_{0.6}$N$_{0.4}$ leads to superconductivity with a transition
temperature (T$_c$) of ~2.6 K, about five times higher than that of TiO at ~0.5
K and half as high as the T$_c$ of ~6 K in titanium nitride (TiN). However,
Eliashberg theoretical calculations predict similar Tc in TiO, Ti oxynitride
and TiN. The analysis of electron mean free path suggests the presence of
significant disorder in TiO and a remarkable reduction in the impact of
disorder in oxynitrides. Density functional theory (DFT) calculations reveal
that disorder decreases the coherence of electronic states for non-zero
momenta, which would degrade the influence of electron-phonon. Our findings
demonstrate the disorder and superconductivity depend strongly on the N/O
ratio, highlighting the critical role of disorder for superconductivity in this
series of Ti(O,N) materials.
