Thermally Activated Processes of the Phase Composition and Structure Formation of the Nanoscaled Co–Sb Films

Abstract

It is investigated the formation of the phase composition and structure in the nanoscaled CoSb x (30 nm) (1.82 ≤ x ≤ 4.16) films deposited by the method of molecularbeam epitaxy on the substrates of the oxidated monocrystalline silicon at 200°C and following thermal treatment in vacuum in temperature range of 300-700°C. It is established that the films after the deposition are polycrystalline without texture. With increase in Sb content the formation of the phase composition in the films takes place in such sequence as this is provided by phase diagram for the bulky state of the Co-Sb system. At annealing in vacuum at temperature above 450-500°C a sublimation not only of the crystalline Sb phase but from the antimonides occurs. This is reflected on the phase composition change by following chemical reactions: CoSb 2 →(600 ∘ C) Sb↑= CoSb, CoSb 3 →(600 ∘ C) Sb↑=CoSb 2 ,CoSb 3 +Sb↑→(600 ∘ C) CoSb 3 and leads to increase in amount of the CoSb and CoSb 2 phases and decrease in amount of the CoSb 3 . CoSb x (30 nm) (1.8 < x < 4.16) films under investigation are thermostable up to ~350°C.

CoSb3-based skutterudite nanocomposites prepared by cold sintering process with enhanced thermoelectric properties

“…A reduction of the CoSb 3 to 67 %, an increase of the CoSb 2 to 30 % and the presence of some metallic Co as a minority phase (3 %) are obtained, which affect the relative density of the pieces as mentioned above. This composition transformation at 600 °C could be associated with a solid-gas driven reduction reaction inducing the decomposition of oxide into metallic phases based on the Ellingham diagram [46,47] or/and the sublimation of Sb increasing the amount of the CoSb 2 phase and decreasing that of CoSb 3 [48,49] .…”