Epitaxial Ti1-xWxN alloys with 0 less than or equal to x less than or equal to 0.6 were grown on MgO(001) substrates at 500degreesC by ultrahigh vacuum reactive magnetron sputtering from Ti and W targets in pure N-2. X-ray diffraction, transmission electron microscopy (TEM), and cross-sectional TEM show that the 0.3-mum-thick Ti1-xWxN(001) alloys are single crystals with the B1-NaCl structure. Rutherford backscattering spectroscopy investigations indicate that alloys with x greater than or equal to 0.05 are slightly overstoichiometric with NI(Ti + W) = 1.06 +/- 0.05. The alloy lattice parameter a, along the film growth direction is 4.251 A, irrespective of the WN concentration, for x less than or equal to 0.41 and decreases slightly at higher concentrations. TEM analyses show that Ti0.5W0.5N(001) alloys have long-range CuPt-type atomic ordering on the cation sublattice. The room-temperature resistivity increases linearly from 13 muOmega cm for TiN to 287,muOmega cm for Ti0.42W0.58N due primarily to alloy scattering while the temperature coefficient of resistivity is positive in Ti1-xWxN alloys with x less than or equal to 0.21 and negative for x > 0.21 due to weak charge carrier localization. The superconducting critical temperature T-x of Ti1-xWxN alloys initially increases with x, due to a larger density of states at the Fermi level, consistent with valence band x-ray photoelectron spectroscopy measurements. T-x reaches a maximum of 6.67 K at x = 0.21 and decreases for larger x values. (C) 2003 American Vacuum Society.