In 1889 in USA, yttrium silicates were discovered for the first time from yttrialite ore. Yittrium silicates or the Y2O3–SiO2 binary system includes Y2Si2O7, Y2SiO5, and 2Y2O3·3SiO2. After this, different mines were discovered in different parts of the world
such as Japan and Russia. Although the chemical compositions for these yttrialites were the same for the ores taken from different mines, the reported crystal structures showed a wide diversity. Moreover, the crystal structure also varied depending on the heating history.
The crystal structure diversity of yttrialites was found to be the result of
polymorphisms. Bondar and Toropov pointed out that there were three ternarycrystalline phases, namely, Y2SiO5, Y2Si2O7, and 2Y2O3·3SiO2, with melting points of 1980, 1950, and 1750oC, respectively, in the binary Y2O3–SiO2 system. However, according to the later investigations, 2Y2O3·3SiO2 was stable only in the presence of other divalent or monovalent cations.
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