Phase transformation in vacuum and basic physicochemical properties of heterophasic amorphocrystalline Bi2O3-based nanopowder produced by pulsed electron beam evaporation

Abstract

In this work the method of pulsed electron beam evaporation (PEBE) in vacuum (4 Pa) was used to produce the mesoporous multiphase (α, β and amorphous) amorphocrystalline nanopowder (ACN) of Bi2O3 with specific surface area (SSA) up to 23 m2/g. The effect of thermal annealing on the properties of Bi2O3 ACN was investigated in vacuum and in air. Using the HTXRD method in a vacuum (10−4 mbar) in the RT-510 °С temperature range, the phase transformation of the NP was established according to the scheme (α + β + amorph) ⟶200°C(α+β+R)⟶280°C(α+R)⟶510°C(α). The formation of uniform Bi amorphocrystalline nanoparticles (droplets) with a size of 3–5 nm was observed on the surface of all bismuth oxide samples (S200, S300 and S500) that were annealed in air in the temperature range of 200–500 °С, respectively, due to extrusion of liquid Bi from the volume to the surface of large nanoparticles (NPles) forming the framework of 3D nanoparticle agglomerates during the cooling of the annealed NPs. The presence of NPles of metallic Bi in the original sample was confirmed directly by HRTEM and indirectly by RS, DSC and PCL. The magnetic behavior of annealed samples confirmed their diamagnetic nature. The weak ferromagnetic response (3–4 memu/g) in the as prepared sample was associated with its very defective structure. The photocatalytic activity of NPs was confirmed in decomposition of MO colorant during UV irradiation.