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Changbaiite
Changbaiite (PbNb2O6) is a member of the oxide mineral class in which the mineral contains oxygen which is grouped along with one or two metal ion. Changbaiite is classified as a multiple Oxide XY2O6 and it generally has an ionic bond. Furthermore, it is also orthorhombic at a temperature of 25 °C and it changes to orthorhombic-tetragonal at 570 °C.〔Subbarao, E. C., and Shirane, G. (1960) "Nonstoichiometry and Ferroelectric Properties of PbNb2O6-Type Compounds". ''Journal of Chemical Physics', 32, 1846–1851.
(Ferroelectric Properties of PbNb2O6-Type Compounds )〕
==Composition==
The chemical formula of changbaiite is PbNb2O6 after microprobe analysis of kaolinite-filled veins. It is composed of iron (II) oxide FeO 0.94%, lead oxide PbO 41.51%, iron (III) oxide Fe2O3 0.42%, titanium dioxide TiO2 0.95%, niobium pentoxide Nb2O5 55.62%, and tantalum pentoxide Ta2O5 0.98%, which produce the chemical formula (Pb0.95Fe2+0.05)(Nb1.95Ti0.05Fe3+0.02Ta0.01) or PbNb2O6. It was also examined by the spectrographic method which represents Sb 0.3, Si 0.1, Ba 0.2, Ca 0.1, and minor traces of copper, magnesium and aluminum.〔Fleischer, M., Chao, G., and Pabst, A. (1979) "(New Mineral Names )". ''American Mineralogist'', 64, 241–245.〕
Subbarao suggested that Changbaiite formula PbNb2O6 can vary. He represented lead niobate by A1+xNb2O6 where the A site is an ion (usually lead) and he found that the upper limit of x in his representation was about 0.15 and a low limit between −0.07 and −0.08. In conclusion, the formula ranges from Pb0.92Nb2O6 to Pb1.15Nb2O6.〔
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