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Lanthanum gallium silicate

Lanthanum gallium silicate (refer to as LGS in the article), also known as langasite, has a chemical formula of A3BC3D2O14, where A, B, C and D indicate particular cation sites. A is a decahedral (Thomson cube) site coordinated by 8 oxygen atoms. B is octahedral site coordinated by 6 oxygen atoms, and C and D are tetrahedral sites coordinated by 4 oxygen atoms. In this material, lanthanum occupied the A-sites, gallium the B, C and half of D-sites, and, silicon the other half of D-sites. The crystal structure is shown below:

LGS is a piezoelectric material, with no phase transitions up to its melting point of 1470 °C. Single crystal LGS can be grown via Czochralski method, in which crystallization is initiated on a rotating seed crystal lowered into the melt followed by pulling from the melt. The growth atmosphere is usually argon or nitrogen with up to 5% of oxygen. The use of oxygen in the growth environment is reported to suppress gallium loss from the melt; however, too high an oxygen level can lead to platinum (crucible material used for the melt) dissolution in the melt. The growth of LGS is primarily along the Z-direction. Currently the 3-inch (76 mm) langasite boules produced commercially have growth rates of 1.5 to 5 mm/h. The quality of the crystals tends to improve as the growth rate is reduced.

See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lanthanum_gallium_silicate". A list of authors is available in Wikipedia.
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