title: The influence of nanoscale phase separation and devitrification on the electrical transport properties of amorphous Cu-Nb alloy thin films.
abstract: The formation of amorphous phases in immiscible alloys with a large positive enthalpy of mixing is thermodynamically unfavorable. Co-sputter deposited Cu-Nb films exhibit a nanoscale phase separation into Cu-rich and Nb-rich amorphous regions. They show relatively high room temperature resistivity, a negative temperature coefficient of resistance (TCR), and an incomplete superconducting transition with onset at 3.7 K. Annealing the nanophase-separated amorphous films at 200 °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 (T(C))(onset) = 3.7 K. Annealing at 350 °C leads to complete devitrification via the formation of large bcc Nb-rich grains encapsulating the 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 electrical transport and superconducting behavior appear to be consistent with a two-stage crystallization process.
authors.affiliation: Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai 400005, India.
authors.forename: Sangita
authors.initials: S
authors.lastname: Bose
authors.forename: Anantha
authors.initials: A
authors.lastname: Puthucode
authors.forename: Rajarshi
authors.initials: R
authors.lastname: Banerjee
authors.forename: Pushan
authors.initials: P
authors.lastname: Ayyub