New method for obtaining dispersed β-Bi ₂ O ₃ and possibility of thermal stabilization by introduction of Ce

The research presented in this work is aimed at evaluating the possibility of using the sorbitol bismuth complex as a new precursor for conducting low-temperature synthesis of β-Bi2O3. The obtained β-Bi2O3 is free from impurities of other polymorphic modifications of Bi2O3. The morphology, structure, optical properties, and thermal stability of the obtained β-Bi2O3 have been studied. The oxidative pyrolysis of the bismuth sorbitol complex has been investigated. It has been shown that at a molar ratio of Bi(NO3)3·5H2O/sorbitol equal to 2.8:1, the product is β-Bi2O3. The pyrolysis proceeds in two main stages. The first stage is low-temperature (completed before 130 °C) and proceeds at a high rate. The second stage is likely associated with the decomposition of bismuth oxynitrates of variable composition. The β-Bi2O3 obtained with this method has a surface area of 6.4 m2/g due to its developed porous structure. Within the framework of the proposed method, the possibility of doping β-Bi2O3 (using cerium as an example, 5% at.) has been investigated. It has been shown that this ensures the manifestation of photochromic properties of β-Bi2O3. Thermal stability of β-Bi2O3 under isothermal conditions (10 h) also increases from 350 °C to 500 °C. Under conditions of dynamic heating in the presence of a dopant, the onset of the β→α phase transition shifts from 479.5 °C to 676.1 °C. The obtained β-Bi2O3 is characterized by a bandgap value of 2.35 eV. Doping with cerium narrows the band gap of β-Bi2O3 to 2.27 eV due to the shift of the long-wave absorption edge into the visible region of the spectrum.