Lanthanum gallium silicate
Chemical compound From Wikipedia, the free encyclopedia
Lanthanum gallium silicate (referred to as LGS in this article), also known as langasite, has a chemical formula of the form 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.[1]
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| Names | |
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| Other names
LGS or langasite | |
| Identifiers | |
3D model (JSmol) |
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| Properties | |
| Ga5La3O14Si | |
| Molar mass | 1017.402 g·mol−1 |
| Appearance | colorless solid |
| Density | 5.75 g/cm3 |
| Melting point | 1,470 °C (2,680 °F; 1,740 K) |
| insoluble | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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LGS is a piezoelectric material,[2] with no phase transitions up to its melting point of 1470 °C. Single crystal LGS can be grown via the Czochralski method, in which crystallization is initiated on a rotating seed crystal lowered into the melt followed by pulling from the melt.[3] 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.
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