Comprehensive study investigates phase transitions and thermal stability in Co–Ni thin films, suggesting implications for material performance.
Nanocrystalline Co–Ni thin films were successfully synthesized via electrodeposition on copper substrates using a sulfate-chloride bath containing thiourea as a grain refiner. The influence of Ni2+/Co2+ molar ratio on the chemical composition, structural evolution, and thermal stability was systematically investigated. ICP-OES analysis confirmed the anomalous codeposition mechanism, where Co enrichment in the deposits is proportional to its concentration in the electrolyte. Rietveld refinement of XRD patterns revealed a significant phase transition from a Face-Centered Cubic (FCC) dominated structure to a Hexagonal Close-Packed (HCP) phase (up to 80.04%) as the Co content in the bath increased. The incorporation of sulfur (S) from thiourea induced severe lattice distortion, reducing crystallite size to approximately 14 nm while simultaneously increasing microstrain. Differential Scanning Calorimetry (DSC) identified three distinct thermal processes: structural relaxation (40–270°C), HCP↔FCC allotropic transformation (410–420°C), and high-temperature grain coarsening. The 70% Co alloy exhibited the highest thermal stability, suggesting that optimized composition and impurity-induced grain refinement can significantly enhance the metastable properties of electrodeposited iron-group alloys.
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Bouzit et al. (2026) studied this question.
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