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 convent ...

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 (aluminiu ...

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 tab ...

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 Stress (mechanics), mechanical s ...

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 abu ...

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 se ...

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 wel ...

. 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". Platinu ...

(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

External links