Bismuth oxide's classification

1. Classification of Bismuth oxide

Bismuth (III) oxide is an important compound of Bismuth, Bismuth oxide has two kinds of crystal structure: Alpha type and Beta type. Compared with beta Bismuth oxide, alpha Bismuth oxide is more stable in high temperature and has more common use of electronic materials, thermistor, glass coloring, varistor, surge arresters, CRT, fireproof paper, nuclear reactor fuel, electronic etc. 

Bismuth oxide has seen interest as a material for solid oxide fuel cells or SOFCs since it is an ionic conductor, i.e. oxygen atoms readily move through it. Pure bismuth oxide, Bi2O3 has four crystallographic polymorphs. It has a monoclinic crystal structure, designated α- Bi2O3, at room temperature. This transforms to the cubic fluorite-type crystal structure, δ-Bi2O3, when heated above 727°C, which remains the structure until the melting point, 824°C, is reached. The behaviour of Bi2O3 on cooling from the δ-phase is more complex, with the possible formation of two intermediate metastable phases; the tetragonal β-phase or the body centred cubic γ-phase. The γ-phase can exist at room temperature with very slow cooling rates, but α- Bi2O3 always forms on cooling the β-phase.

2. δ- Bi2O3 has the highest reported conductivity

At 750°C the conductivity of δ- Bi2O3 is typically about 1 Scm-1, about three orders of magnitude greater than the intermediate phases and four orders greater than the monoclinic phase. The conductivity in the β, γ and δ-phases is predominantly ionic with oxide ions being the main charge carrier. The α-phase exhibits p-type electronic conductivity (the charge is carried by positive holes) at room temperature which transforms to n-type conductivity (charge is carried by electrons) between 550°C and 650°C, depending on the oxygen partial pressure. It is therefore unsuitable for electrolyte applications. δ- Bi2O3 has a defective fluorite-type crystal structure in which two of the eight oxygen sites in the unit cell are vacant. These intrinsic vacancies are highly mobile due to the high polarisability of the cation sub-lattice with the 6s2 lone pair electrons of Bi3+. The Bi-O bonds have covalent bond character and are therefore weaker than purely ionic bonds, so the oxygen ions can jump into vacancies more freely.

3. Classification of bismuth oxide

Bismuth Oxide is mainly used in electronic materials, thermistor, glass coloring, varistor, surge arresters, CRT, fireproof paper, nuclear reactor fuel, electronic etc.