Lithium niobate

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Lithium niobate
Linbo3 Unit Cell.png
LiNbO3.png
__ Li +     __ Nb 5+     __ O 2−
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.583
PubChem CID
Properties
LiNbO3
Molar mass 147.846 g/mol
Appearancecolorless solid
Density 4.65 g/cm3 [1]
Melting point 1,257 °C (2,295 °F; 1,530 K) [1]
None
Band gap 4 eV
no 2.30, ne 2.21 [2]
Structure
trigonal
R3c
3m (C3v)
Hazards
Lethal dose or concentration (LD, LC):
8000 mg/kg (oral, rat) [3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)
Infobox references

Lithium niobate (Li Nb O 3) is a compound of niobium, lithium, and oxygen. Its single crystals are an important material for optical waveguides, mobile phones, piezoelectric sensors, optical modulators and various other linear and non-linear optical applications. It is a human-made dielectric material that does not exist in nature. [4] Lithium niobate is sometimes referred to by the brand name linobate. [5]

Lithium Chemical element with atomic number 3

Lithium is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the lightest metal and the lightest solid element. Like all alkali metals, lithium is highly reactive and flammable, and must be stored in mineral oil. When cut, it exhibits a metallic luster, but moist air corrodes it quickly to a dull silvery gray, then black tarnish. It never occurs freely in nature, but only in compounds, such as pegmatitic minerals, which were once the main source of lithium. Due to its solubility as an ion, it is present in ocean water and is commonly obtained from brines. Lithium metal is isolated electrolytically from a mixture of lithium chloride and potassium chloride.

Niobium Chemical element with atomic number 41

Niobium, formerly known as columbium, is a chemical element with the symbol Nb and atomic number 41. Niobium is a light grey, crystalline, and ductile transition metal. Pure niobium has a hardness similar to that of pure titanium, and it has similar ductility to iron. Niobium oxidizes in the earth's atmosphere very slowly, hence its application in jewelry as a hypoallergenic alternative to nickel. Niobium is often found in the minerals pyrochlore and columbite, hence the former name "columbium". Its name comes from Greek mythology, specifically Niobe, who was the daughter of Tantalus, the namesake of tantalum. The name reflects the great similarity between the two elements in their physical and chemical properties, making them difficult to distinguish.

Oxygen Chemical element with atomic number 8

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 well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O
2
. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up almost half of the Earth's crust.

Contents

Properties

Lithium niobate is a colorless solid insoluble in water. It has a trigonal crystal system, which lacks inversion symmetry and displays ferroelectricity, the Pockels effect, the piezoelectric effect, photoelasticity and nonlinear optical polarizability. Lithium niobate has negative uniaxial birefringence which depends slightly on the stoichiometry of the crystal and on temperature. It is transparent for wavelengths between 350 and 5200 nanometers.

Crystal system Classification of crystalline materials by their three dimensional structural geometry

In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals. Informally, two crystals are in the same crystal system if they have similar symmetries, although there are many exceptions to this.

Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are pyroelectric, with the additional property that their natural electrical polarization is reversible. The term is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment. Ferromagnetism was already known when ferroelectricity was discovered in 1920 in Rochelle salt by Valasek. Thus, the prefix ferro, meaning iron, was used to describe the property despite the fact that most ferroelectric materials do not contain iron. Materials that are both ferroelectric and ferromagnetic are known as multiferroics.

Pockels effect appearance or change of birefringence in an optical medium by an applied electric field

The Pockels effect, or Pockels electro-optic effect, changes or produces birefringence in an optical medium induced by an electric field. In the Pockels effect, also known as the linear electro-optic effect, the birefringence is proportional to the electric field. In the Kerr effect, the refractive index change (birefringence) is proportional to the square of the field. The Pockels effect occurs only in crystals that lack inversion symmetry, such as lithium niobate, and in other noncentrosymmetric media such as electric-field poled polymers or glasses.

Lithium niobate can be doped by magnesium oxide, which increases its resistance to optical damage (also known as photorefractive damage) when doped above the optical damage threshold. Other available dopants are Fe, Zn, Hf, Cu, Gd, Er, Y, Mn and B.

Magnesium oxide chemical compound

Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions held together by ionic bonding. Magnesium hydroxide forms in the presence of water (MgO + H2O → Mg(OH)2), but it can be reversed by heating it to separate moisture.

Iron Chemical element with atomic number 26

Iron is a chemical element with symbol Fe and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust.

Zinc Chemical element with atomic number 30

Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a blue-silvery appearance when oxidation is removed. It is the first element in group 12 of the periodic table. In some respects zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of similar size. Zinc is the 24th most abundant element in Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest workable lodes are in Australia, Asia, and the United States. Zinc is refined by froth flotation of the ore, roasting, and final extraction using electricity (electrowinning).

Growth

Single crystals of lithium niobate can be grown using the Czochralski process. [6]

Single crystal material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries

A single crystal or monocrystalline solid is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries. The absence of the defects associated with grain boundaries can give monocrystals unique properties, particularly mechanical, optical and electrical, which can also be anisotropic, depending on the type of crystallographic structure. These properties, in addition to making them precious in some gems, are industrially used in technological applications, especially in optics and electronics.

Czochralski process Method of crystal growth

The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors, metals, salts and synthetic gemstones. The process is named after Polish scientist Jan Czochralski, who invented the method in 1915 while investigating the crystallization rates of metals. He made this discovery by accident: instead of dipping his pen into his inkwell, he dipped it in molten tin, and drew a tin filament, which later proved to be a single crystal.

A Z-cut, single crystal Lithium Niobate wafer Lithium Niobate Wafer.jpg
A Z-cut, single crystal Lithium Niobate wafer

After a crystal is grown, it is sliced into wafers of different orientation. Common orientations are Z-cut, X-cut, Y-cut, and cuts with rotated angles of the previous axes. [7]

Nanoparticles

Nanoparticles of lithium niobate and niobium pentoxide can be produced at low temperature. [8] The complete protocol implies a LiH induced reduction of NbCl5 followed by in situ spontaneous oxidation into low-valence niobium nano-oxides. These niobium oxides are exposed to air atmosphere resulting in pure Nb2O5. Finally, the stable Nb2O5 is converted into lithium niobate LiNbO3 nanoparticles during the controlled hydrolysis of the LiH excess. [9] Spherical nanoparticles of lithium niobate with a diameter of approximately 10 nm can be prepared by impregnating a mesoporous silica matrix with a mixture of an aqueous solution of LiNO3 and NH4NbO(C2O4)2 followed by 10 min heating in an IR furnace. [10]

Nanoparticle Particle with size between 1 and 100 nm with an outer layer

Nanoparticles are particles between 1 and 100 nanometres (nm) in size with a surrounding interfacial layer. The interfacial layer is an integral part of nanoscale matter, fundamentally affecting all of its properties. The interfacial layer typically consists of ions, inorganic and organic molecules. Organic molecules coating inorganic nanoparticles are known as stabilizers, capping and surface ligands, or passivating agents. In nanotechnology, a particle is defined as a small object that behaves as a whole unit with respect to its transport and properties. Particles are further classified according to diameter.

Niobium pentoxide chemical compound

Niobium pentoxide is the inorganic compound with the formula Nb2O5. It is a colourless insoluble solid that is fairly unreactive. It is the main precursor to all materials made of niobium, the dominant application being alloys, but other specialized applications include capacitors, lithium niobate, and optical glasses.

Applications

Lithium niobate is used extensively in the telecoms market, e.g. in mobile telephones and optical modulators. [11] It is the material of choice for the manufacture of surface acoustic wave devices. For some uses it can be replaced by lithium tantalate, Li Ta O 3. Other uses are in laser frequency doubling, nonlinear optics, Pockels cells, optical parametric oscillators, Q-switching devices for lasers, other acousto-optic devices, optical switches for gigahertz frequencies, etc. It is an excellent material for manufacture of optical waveguides. It's also used in the making of optical spatial low-pass (anti-aliasing) filters.

In the past few years lithium niobate is finding applications as a kind of electrostatic tweezers, an approach known as optoelectronic tweezers as the effect requires light excitation to take place. [12] [13] This effect allows for fine manipulation of micrometer-scale particles with high flexibility since the tweezing action is constrained to the illuminated area. The effect is based on the very high electric fields generated during light exposure (1–100 kV/cm) within the illuminated spot. These intense fields are also finding applications in biophysics and biotechnology, as they can influence living organisms in a variety of ways. [14] For example, iron-doped lithium niobate excited with visible light has been shown to produce cell death in tumoral cell cultures. [15]

Periodically-poled lithium niobate (PPLN)

Periodically-poled lithium niobate (PPLN) is a domain-engineered lithium niobate crystal, used mainly for achieving quasi-phase-matching in nonlinear optics. The ferroelectric domains point alternatively to the +c and the −c direction, with a period of typically between 5 and 35 µm. The shorter periods of this range are used for second harmonic generation, while the longer ones for optical parametric oscillation. Periodic poling can be achieved by electrical poling with periodically structured electrode. Controlled heating of the crystal can be used to fine-tune phase matching in the medium due to a slight variation of the dispersion with temperature.

Periodic poling uses the largest value of lithium niobate's nonlinear tensor, d33 = 27 pm/V. Quasi-phase matching gives maximum efficiencies that are 2/π (64%) of the full d33, about 17 pm/V. [16]

Other materials used for periodic poling are wide band gap inorganic crystals like KTP (resulting in periodically poled KTP, PPKTP), lithium tantalate, and some organic materials.

The periodic poling technique can also be used to form surface nanostructures. [17] [18]

However, due to its low photorefractive damage threshold, PPLN only finds limited applications: at very low power levels. MgO-doped lithium niobate is fabricated by periodically-poled method. Periodically-poled MgO-doped lithium niobate (PPMgOLN) therefore expands the application to medium power level.

Sellmeier equations

The Sellmeier equations for the extraordinary index are used to find the poling period and approximate temperature for quasi-phase matching. Jundt [19] gives

valid from 20 to 250 °C for wavelengths from 0.4 to 5 micrometers, whereas for longer wavelength, [20]

which is valid for T = 25 to 180 °C, for wavelengths λ between 2.8 and 4.8 micrometers.

In these equations f = (T − 24.5)(T + 570.82), λ is in micrometers, and T is in °C.

More generally for ordinary and extraordinary index for MgO-doped Li Nb O 3:

,

with:

Parameters5% MgO-doped CLN1% MgO-doped SLN
nenone
a15.7565.6535.078
a20.09830.11850.0964
a30.20200.20910.2065
a4189.3289.6161.16
a512.5210.8510.55
a61.32×10−21.97×10−21.59×10−2
b12.860×10−67.941×10−74.677×10−7
b24.700×10−83.134×10−87.822×10−8
b36.113×10−8−4.641×10−9−2.653×10−8
b41.516×10−4−2.188×10−61.096×10−4

for congruent Li Nb O 3 (CLN) and stochiometric Li Nb O 3 (SLN). [21]

See also

Related Research Articles

Pyroelectricity property of certain crystals which are naturally electrically polarized and contain large electric fields

Pyroelectricity is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields. Pyroelectricity can be described as the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change gives rise to a voltage across the crystal. If the temperature stays constant at its new value, the pyroelectric voltage gradually disappears due to leakage current.

Polaritonics is an intermediate regime between photonics and sub-microwave electronics. In this regime, signals are carried by an admixture of electromagnetic and lattice vibrational waves known as phonon-polaritons, rather than currents or photons. Since phonon-polaritons propagate with frequencies in the range of hundreds of gigahertz to several terahertz, polaritonics bridges the gap between electronics and photonics. A compelling motivation for polaritonics is the demand for high speed signal processing and linear and nonlinear terahertz spectroscopy. Polaritonics has distinct advantages over electronics, photonics, and traditional terahertz spectroscopy in that it offers the potential for a fully integrated platform that supports terahertz wave generation, guidance, manipulation, and readout in a single patterned material.

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Potassium titanyl phosphate chemical compound

Potassium titanyl phosphate (KTP) is an inorganic compound with the formula KTiOPO4. It is a white solid. KTP is an important nonlinear optical material that is commonly used for frequency doubling diode pumped solid-state lasers such as Nd:YAG and other neodymium-doped lasers.

Barium titanate chemical compound

Barium titanate is an inorganic compound with chemical formula BaTiO3. Barium titanate appears white as a powder and is transparent when prepared as large crystals. It is a ferroelectric ceramic material that exhibits the photorefractive effect and piezoelectric properties. It is used in capacitors, electromechanical transducers and nonlinear optics.

In physics, photon-induced electric field poling is a phenomenon whereby a pattern of local electric field orientations can be encoded in a suitable ferroelectric material, such as perovskite. The resulting encoded material is conceptually similar to the pattern of magnetic field orientations within the magnetic domains of a ferromagnet, and thus may be considered as a possible technology for computer storage media. The encoded regions are optically active and thus may be "read out" optically.

The electrogyration effect is the spatial dispersion phenomenon, that consists in the change of optical activity (gyration) of crystals by a constant or time-varying electric field. Being a spatial dispersion effect, the induced optical activity exhibit different behavior under the operation of wave vector reversal, when compared with the Faraday effect: the optical activity increment associated with the electrogyration effect changes its sign under that operation, contrary to the Faraday effect. Formally, it is a special case of gyroelectromagnetism obtained when the magnetic permeability tensor is diagonal.

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Talbot effect

The Talbot effect is a near-field diffraction effect first observed in 1836 by Henry Fox Talbot. When a plane wave is incident upon a periodic diffraction grating, the image of the grating is repeated at regular distances away from the grating plane. The regular distance is called the Talbot length, and the repeated images are called self images or Talbot images. Furthermore, at half the Talbot length, a self-image also occurs, but phase-shifted by half a period. At smaller regular fractions of the Talbot length, sub-images can also be observed. At one quarter of the Talbot length, the self-image is halved in size, and appears with half the period of the grating. At one eighth of the Talbot length, the period and size of the images is halved again, and so forth creating a fractal pattern of sub images with ever-decreasing size, often referred to as a Talbot carpet.

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Micro-pulling-down method of growing crystals

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Niobium oxychloride chemical compound

Niobium oxychloride is the inorganic compound with the formula NbOCl3. It is a white, crystalline, diamagnetic solid. It is often found as an impurity in samples of niobium pentachloride, a common reagent in niobium chemistry.

Strontium barium niobate

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Niobium diselenide chemical compound

Niobium diselenide or niobium(IV) selenide is a layered transition metal dichalcogenide with formula NbSe2. Niobium diselenide is a lubricant, and a superconductor at temperatures below 7.2 K that exhibit a charge density wave (CDW). NbSe2 crystallizes in several related forms, and can be mechanically exfoliated into monatomic layers, similar to other transition metal dichalcogenide monolayers. Monolayer NbSe2 exhibits very different properties from the bulk material, such as of Ising superconductivity, quantum metallic state, and strong enhancement of the CDW.

References

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Further reading