ИСТИНА

In this work, we examined the phase formation mechanism of BiCuSeO oxyselenides fabricated via reactive spark plasma sintering (RSPS) using (a) Bi2O3, Bi, Se and Cu or (b) Bi, Se and CuO as starting materials. The BiCuSeO phase was directly formed in bulk from mechanically activated precursor’s stoichiometric mixture during RSPS. It was observed, that single phase bulk BiCuSeO oxyselenides can be obtained for both (a) and (b) precursors. While for samples obtained by conventional solid-state route (SSR) followed by SPS there was no significant difference in the phase composition and density of the final BiCuSeO bulk samples, the relative density of the samples obtained using one-step RSPS process was strongly affected by the used reaction. Thus, the density of the RSPSed samples did not exceed 90% and was not less than 97%, for (a) and (b) reactions, respectively. Our thermodynamic calculations revealed that the formation of BiCuSeO using CuO, Bi and Se (b) requires lower activation energy and has larger thermodynamic driving force compared to than that for the reaction through the Bi2O3, Bi, Se and Cu (a) as precursors. Moreover, according to X-ray phase analysis, the BiCuSeO phase formation mechanism through the reaction (a) was more complicated with complex intermediate phase formed before the main BiCuSeO phase, while for the reaction (b) BiSe and CuO directly formed BiCuSeO. Additionally, it was revealed that phase formation mechanism in bulk during RSPS was similar to that for samples fabricated by mechanical alloying and self-propagating high-temperature synthesis in powder form [1,2].