Polymorphism of bismuth sesquioxide. I. Pure Bi2O3

Abstract

Stabili ty relationships of t he four p oly m orp hs of bismu t h oxide have been dct erJlIin ed by m eans of DTA a nd high-temperat ure x-ray studies. The stable low-temperature m onoclinic form t ransform s to the stabl e cubic form at 730 ± 5 ac, whi ch then m elts at 825 ± 5 ac.By controlled coolin g, t he m etastable tetragonal ph ase and/ o r t he metastable bod v-ce n te red cubic (b. c.c.) phase ap pear at about 645 ac. Wh ereas b. c.e. can be prese r ved to i·oom temperature, tetrago na l \\"ill transform to m onocli nic bct\\'een 550 a nd 500 ac. T etragona l Bi, 0 3, h owever, is easil y prepa red by decom posin g bismu t ite (B i, 0 3·CO,) at 400 ac for se vera l h ours. Th e g reatest transit ion expa nsion occurs at t h e m on ocl inic to cubic in versio n, an d cubi c 13i,03 shows t he g reatest coeffi cient of vo lum e expansion. vVi th exposure to a ir, 13 i, 0 3 carbo nates a nd pa r tiall y t ra nsforms to bismu tite a nd a n u nkno,yn ph ase.

Chemically stabilized δ-Bi2O3 phase: Raman scattering and X-ray diffraction studies

“…It has been shown that Bi 2 O 3 exists under various isomorphous phases that are: á-, â-, c-and δ-Bi 2 O 3 [6][7][8] . At room temperature and up to 730°C, Bi 2 O 3 exists in a monoclinic á-phase [1][2][3] .…”

“…At about 550°C, it usually transforms back into á-phase. If the sample is not heated over 748°C, it will revert back into á-phase directly after a hysteresis at about 700°C 6 . Interestingly, the high temperature cubic polymorph d-phase of Bi 2 O 3 presents peculiar conductive properties.…”

Synthesis of Bi₂O₃–ZrO₂ solid solutions for environment-friendly orange pigments

“…8) Therefore, mixtures of Bi 2 O 3 and ZrO 2 powders were heated at 800°C to credibly synthesize the solid solutions.…”

Estudio termodinámico de la región rica en Bi₂O₃ del sistema Bi₂O₃-ZnO

“…Bi 2 O 3 present four polymorphic (8,9) forms at normal pressure, which are known as the α-, β-, γ-, and δ-forms. All polymorphic modifications have been structurally characterized and their powder diffraction patterns discussed (8,9,10).…”

“…All polymorphic modifications have been structurally characterized and their powder diffraction patterns discussed (8,9,10). At atmospheric pressure, the monoclinic α-Bi 2 O 3 is stable up to 729ºC, above this temperature transforms to the cubic δ-Bi 2 O 3 that is stable up to the melting point of 824ºC.…”