Thermal evolution of Co_1−x-P_x electrodeposited ribbons and its influence on the electrical resistivity

Abstract

Co-P ribbons have been obtained by electrodeposition on aluminium substrates. The effect of changing the current density (in the range 8–19 A dm⁻²) and the H₃PO₃ concentration on the nature of the phases present in the “as-prepared” samples and their thermal evolution has been studied by X-ray diffraction analysis and differential scanning calorimetry. Amorphous and crystalline (fully or partly) products have been obtained, by changing the bath composition. Devitrification of the initially amorphous samples leads to cobalt (in the hexagonal and/or cubic form) and cobalt phosphide (Co₂P) crystalline phases. A devitrification mechanism has been proposed. The presence of two amorphous phases in the glassy samples and the possibility of obtaining intermediate samples with crystalline and amorphous phases intermixed with each other, is suggested from the experimental results. The electrical resistivities of the products obtained have been measured. They are affected by the phosphorus content and develop after thermal treatments, in agreement with both microstructure changes and the nature of the crystalline cobalt phases formed.