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 An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

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 Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lantha ...

occupied the ''A''-sites,

gallium Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group ( alum ...

the ''B'', ''C'' and half of ''D''-sites, and,

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

the other half of ''D''-sites. LGS is a

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ' ...

material,Polishing and Etching Langasite and Quartz
Laffey SH and Vig JR, 1994 IEEE International Frequency Control Symposium with no phase transitions up to its melting point of 1470 °C. Single crystal LGS can be grown via the

Czochralski method The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, platinum, silver, ...

, 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 Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as a ...

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...

with up to 5% of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

. The use of

in the growth environment is reported to suppress

loss from the melt; however, too high an

level can lead to

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...

(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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Properties of a langasite crystal
Lanthanum compounds Gallium compounds Silicates Piezoelectric materials Ceramic materials

See also

References

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