Lithium niobate

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Crystal structure
Structure of lithium niobate
__ Li +      __ Nb 5+      __ O 2−
Crystal system

trigonal

Space group

R 3 c (No. 161)Template: room group / 161

Lattice parameters

a = 515 pm
c = 1386 pm

Coordination numbers

Li [12] (6 + 6), Nb [6], O [6] (4 + 2)

General
Surname Lithium niobate
other names

Lithium niobium oxide

Ratio formula LiNbO 3
Brief description

whitish, odorless solid

External identifiers / databases
CAS number 12031-63-9
EC number 234-755-4
ECHA InfoCard 100,031,583
PubChem 159404
ChemSpider 10605804
Wikidata Q424481
properties
Molar mass 147.85 g mol −1
Physical state

firmly

density

4.64 g cm −3

Melting point

1275 ° C

Refractive index

2.2871 (23 ° C)

safety instructions
GHS labeling of hazardous substances
no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
Toxicological data

8000 mg kg −1 ( LD 50ratoral )

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 .

Crystal structure

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 . Template: room group / 161

Physical Properties

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) ). Template: room group / 167

Manufacturing

Lithium niobate can be obtained, for example, by solid-state or melt reaction of lithium carbonate with niobium (V) oxide .

Nanoparticles

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

Similar connections

The lithium tantalate LiTaO 3 crystallizes isotypically to LiNbO 3 , that is, it has the same crystal structure .

See also

literature

  • AM Prokhorov, Yu S. Kuz'minov: Physics and Chemistry of Crystalline Lithium Niobate . Institute of Physics Publishing, 1999, ISBN 0-85274-002-6 .
  • A. Räuber: Chemistry and physics of lithium niobate . In: Current Topics in Materials Science . tape 1 . Elsevier Science Publishing, 1978, ISBN 0-7204-0708-7 , pp. 481-601 .
  • RS Weis, TK Gaylord: Lithium niobate: Summary of physical properties and crystal structure . In: Applied Physics A: Materials Science & Processing . tape 37 , no. 4 , 1985, pp. 191-203 , doi : 10.1007 / BF00614817 .

Individual evidence

  1. a b c d e data sheet Lithium niobium oxide, Puratronic®, 99.998% (metals basis excluding Ta), Ta <50ppm from AlfaAesar, accessed on December 6, 2019 ( PDF )(JavaScript required) .
  2. lithium niobate, LiNbO3 at Almaz Optics, accessed on August 23, 2011th
  3. A. Alcázar de V., B. Ramiro, J. Rams, B. Alonso, G. Rojo, V. Bermúdez, JM Cabrera: Temperature effects in proton exchanged LiNbO3 waveguides . In: Applied Physics B . 79, No. 7, 2004, pp. 845-849. doi : 10.1007 / s00340-004-1646-8 .
  4. Jump up ↑ R. Hsu, EN Maslen, D. du Boulay, N. Ishizawa: Synchrotron X-ray Studies of LiNbO 3 and LiTaO 3 . In: Acta Crystallographica Section B Structural Science . tape 53 , no. 3 , May 1997, p. 420-428 , doi : 10.1107 / S010876819600777X .
  5. ^ A b K. K. Wong: Properties of Lithium Niobate. Emis. Datareviews Series, No. 28, London 2002, ISBN 0-85296-799-3 .
  6. H. Lehnert, H. Boysen, F. Frey, A. Hewat, P. Radaelli: A neutron powder investigation of the high-temperature structure and phase transition in stoichiometric LiNbO3 . In: Journal of Crystallography . tape 212 , no. 10 , 1997, pp. 712-719 , doi : 10.1524 / zkri.1997.212.10.712 .
  7. Annett Grigas and Stefan Kaskel :: Synthesis of LiNbO 3 nanoparticles in a mesoporous matrix . In: Open Access Beilstein Journal of Nanotechnology . tape 2 , 2011, p. 28-33 , doi : 10.3762 / bjnano.2.3 .