Abstract
The formation of amorphous phases in immiscible alloys with a large positive enthalpy ofmixing is thermodynamically unfavorable. Co-sputter deposited Cu–Nb filmsexhibit a nanoscale phase separation into Cu-rich and Nb-rich amorphous regions.They show relatively high room temperature resistivity, a negative temperaturecoefficient of resistance (TCR), and an incomplete superconducting transitionwith onset at 3.7 K. Annealing the nanophase-separated amorphous films at200 °C results in the nucleation of fcc Cu-rich nanocrystals within an Nb-rich amorphous matrix.This film exhibits multiple resistance steps, eventually showing a sharp drop with(TC)onset = 3.7 K.Annealing at 350 °C leads to complete devitrification via the formation of large bcc Nb-rich grains encapsulatingthe existing fcc Cu nanocrystals. These films show low room temperature resistivity,positive TCR, and a sharp superconducting transition with onset at 5.2 K. The electricaltransport and superconducting behavior appear to be consistent with a two-stagecrystallization process.
Published Version
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