StoichiometricNb3Snfilms on sapphire were prepared with a tin vapor diffusion process from sputtered Nb precursors. The superconductive properties of the precursor and the converted films were measured at 1 kHz and 87 GHz. The nanocrystalline Nb films yieldedTc=7.8–9.3 K,&Dgr;Tc=0.05–0.30 K,Jc(4.2 K)=0.8–2.8 MA/cm2,and&rgr;(Tc)=1–35 &mgr;&OHgr; cm,indicating a high sensitivity to granularity and impurities. In contrast, the 0.5–3.0 &mgr;m thick and large-grainedNb3Snfilms showed reproduciblyTc=18.0 K,&Dgr;Tc=0.1 K,Jc(4.2 K)=5–6.5 MA/cm2,and&rgr;(Tc)=7.7–9.1 &mgr;&OHgr; cm.A reduced energy gap&Dgr;/kTc=1.8–2.2and a penetration depth&lgr;0(T=0 K)=65–80 nmwere deduced from the surface impedance measurements. The residual surface resistance dropped below the sensitivity limit of 0.3 m&OHgr;. ©1997 American Institute of Physics.