Growth, structure, and physical properties of single-phase metastable fcc Cu1−<i>x</i>Cr<i>x</i> solid solutions

Abstract

Single-phase fcc-structure metastable Cu1−xCrx alloys have been grown with Cr concentrations of up to 23 at. %. The films, which were typically 1.5–3 μm thick, were deposited by rf co-sputter deposition onto glass and oxidized-Si substrates at temperature between 55 and 180 °C. The average grain size of alloys grown at 90 °C was ∼100 nm. The lattice parameter of Cu1−xCrx was found to increase linearly with x resulting in an effective fcc Cr radius, in solution, of 0.1332 nm. ∼7% larger than the elemental bcc Cr bonding radius. The room-temperature resistivity of these alloys also increased linearly with x at a rate of 2.8 μΩ cm per at. % Cr. This high differential resistivity was due, in addition to simple alloys scattering, to scattering of conduction electrons into virtual bound states associated with the Cr atoms. Cu0.9Cr0.1 alloys were found to be stable for 24-h anneals at temperatures up to ∼300 °C. From an analysis of x-ray diffraction peak positions and widths as a function of both growth and annealing temperatures, we conclude that the reaction path for the phase transition from the metastable to the equilibrium state involves first the precipitation of coherent fcc Cr particles followed by a transformation to bcc Cr as phase separation continues. The oxidation rate of Cu0.9Cr0.1 was found to be much less that that of pure Cu. At an annealing temperature of 250 °C, the oxide thickness tox on Cu0.9Cr0.1 saturated at J25 nm after 1 h while tox on Cu continued to increase parabolically with time from ∼60 nm at 1 h to 140 nm at 4 h.