|__ Li + __ Nb 5+ __ O 2−|
R 3 c (No. 161)
a = 515 pm
Li  (6 + 6), Nb , O  (4 + 2)
Lithium niobium oxide
|Ratio formula||LiNbO 3|
whitish, odorless solid
|External identifiers / databases|
|Molar mass||147.85 g mol −1|
4.64 g cm −3
1275 ° C
2.2871 (23 ° C)
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C|
Lithium niobate is a chemical compound with the formula LiNbO 3 . It is a transparent, crystalline solid that does not occur naturally. Lithium niobate crystals are usually drawn from a melt (mixture of lithium oxide and niobium (V) oxide ) using the Czochralski process . Due to its crystal structure, it has some technically useful properties, especially as a material in non-linear optics .
Lithium niobate crystallizes in the trigonal crystal system in the space group R 3 c (space group no. 161) with the lattice parameters a = 515 pm and c = 1386 pm and six formula units per unit cell. The Nb 5+ cations are each surrounded by six oxygen atoms in the form of distorted octahedra . These [NbO 6 ] connect via common corners to form a three-dimensional network. The Li + cations are located in the gaps in the network, each of which is surrounded by twelve oxygen atoms. The coordination number of 12 can be described as 6 + 6, since six of the oxygen atoms are significantly further apart from lithium. The coordination polyhedron for lithium is a strongly distorted anti-cuboctahedron .
Lithium niobate crystallizes as a colorless solid with a wide transparency range starting in the near UV to the middle IR range, corresponding to wavelengths from 320 to 5600 nm. Lithium niobate is birefringent and has refractive indices of n o = 2.286 and n e = 2.202 at 633 nm .
The crystals have a Mohs hardness of 5. Lithium niobate shows a number of physical effects: the stoichiometric composition (LiNbO 3 ) is ferroelectric below the Curie temperature T c of 1213 ° C (1486 K) and therefore optically non-linear , electro-optical , photorefractive , elasto-optic , piezoelectric and pyroelectric . The ferroelectric Curie temperature depends on the composition; for the congruent composition (produced from 48.45% Li 2 O, 51.55% Nb 2 O 5 ) it is 1143 ° C. (1416 K). Above the Curie temperature, the material loses its ferroelectric properties and changes to the paraelectric phase (space group R 3 c (No. 167) ).
Lithium niobate nanoparticles are produced by impregnating porous carrier substances with solutions of metal salts with subsequent calcination and dissolution of the carrier matrix or by hydrothermal processes. Spherical nanoparticles with a diameter of 10 nm can be produced by impregnating a mesoporous silicate matrix with an aqueous solution of LiNO 3 and NH 4 NbO (C 2 O 4 ) 2 and then heating in an infrared oven for ten minutes.
Areas of application
- Interdigital transducer and based on it
- Bandpass filters ( surface acoustic wave filters ) in high-frequency circuits, e.g. B. Cell phones and televisions
- Integrated optics
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