Cadmium telluride - Citizendia

Cadmium telluride
Image:Cadmium telluride.jpg
Other names	Irtran-6
Identifiers
CAS number	[1306-25-8]
Properties
Molecular formula	Cd Te
Molar mass	240. CAS registry numbers are unique numerical identifiers for Chemical compounds Polymers biological sequences mixtures and Alloys They are also referred to A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Cadmium (ˈkædmiəm is a Chemical element with the symbol Cd and Atomic number 48 Tellurium (tɪˈlʊəriəm/ /tɛl- is a Chemical element that has the symbol Te and Atomic number 52 Molar mass, symbol M, is the Mass of one mole of a substance ( Chemical element or Chemical compound) 01 g/mol
Density	5. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 85 g/cm³
Melting point	1092 °C
Boiling point	1130 °C
Solubility in other solvents	insoluble
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Cadmium telluride (CdTe) is a crystalline compound formed from cadmium and tellurium with a zinc blende (cubic) crystal structure (space group F43m). The melting point of a solid is the temperature range at which it changes state from solid to Liquid. The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. In Chemistry, the standard state of a material is its state at 1 bar (100 Kilopascals exactly In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. Cadmium (ˈkædmiəm is a Chemical element with the symbol Cd and Atomic number 48 Tellurium (tɪˈlʊəriəm/ /tɛl- is a Chemical element that has the symbol Te and Atomic number 52 Sphalerite (( Zn, Fe) S) is a Mineral that is the chief Ore of Zinc. The space group of a Crystal or crystallographic group is a mathematical description of the Symmetry inherent in the structure In the bulk crystalline form it is a direct bandgap semiconductor. In Semiconductor Physics, a direct Bandgap means that the minimum energy of the Conduction band lies directly above the maximum energy of the A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that CdTe is also a strong solar cell material. A solar cell or photovoltaic cell is a device that converts Solar energy into Electricity by the photovoltaic effect. It is usually sandwiched with cadmium sulfide to form a p-n junction photovoltaic solar cell. Cadmium sulfide is a chemical compound with the formula CdS. Cadmium sulfide is yellow in colour and is a semiconductor A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact Photovoltaics ( PV) is the field of technology and research related to the application of Solar cells for Energy by converting Sunlight directly

1 Applications
2 Physical properties
3 Chemical properties
4 Toxicity
5 New Theoretical Model
6 See also
7 References
8 External links

Applications

CdTe is a useful material for solar cells (photovoltaics). Photovoltaics ( PV) is the field of technology and research related to the application of Solar cells for Energy by converting Sunlight directly At Tellurium and polysilicon prices as of May 2008, thin-film CdTe provides a cost-effective solar cell design, but at a lower efficiency than polysilicon. Tellurium (tɪˈlʊəriəm/ /tɛl- is a Chemical element that has the symbol Te and Atomic number 52 CdTe can be alloyed with mercury to make a versatile infrared detector material (HgCdTe). Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum An infrared detector is a Photodetector that reacts to Infrared (IR Radiation. HgCdTe or mercury Cadmium Telluride (also cadmium mercury telluride, MCT or CMT) is an Alloy of CdTe alloyed with a small amount of zinc makes an excellent solid-state x-ray and gamma ray detector (CdZnTe). Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Cadmium zinc telluride, (CdZnTe or CZT, is (as the name indicates a compound of Cadmium, Zinc and Tellurium or more strictly speaking an alloy

CdTe is used as an infrared optical material for optical windows and lenses but it has small application and is limited by its toxicity such that few optical houses will consider working with it. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of The meaning of this term depends on the context In Astronomy, the optical window is the optical portion of the Electromagnetic spectrum that passes through A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging An early form of CdTe for IR use was marketed under the trademarked name of Irtran-6 but this is obsolete.

CdTe is also applied for electrooptical modulators. It has highest electrooptical coefficient of the linear electrooptic effect among II-VI compound crystals (r₄₁=r₅₂=r₆₃=6. 8*10^-12 m/V).

Physical properties

Lattice constant: 0. The Lattice Constant refers to the constant distance between Unit cells in a Crystal lattice. 648 nm at 300K
Young's modulus: 52 GPa
Poisson ratio: 0. In Solid mechanics, Young's modulus (E is a measure of the Stiffness of an isotropic elastic material Poisson's ratio ( ν) named after Simeon Poisson, is the ratio of the relative contraction strain, or transverse strain (normal to 41

Thermal Properties

Thermal conductivity: 6. In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. 2 W. m^-1. K^-1 at 293 K
Specific heat capacity: 210 J. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity kg^-1. K^-1 at 293 K
Thermal expansion coefficient: 5. When the Temperature of a substance changes the energy that is stored in the Intermolecular bonds between atoms changes 9x10^-6 K^-1 at 293 K

Electronic properties

The direct band gap is 1. 56 eV at 300 K.
Electron effective mass 0. In Solid state physics, a particle's effective mass is the Mass it seems to carry in the semiclassical model of transport in a Crystal. 11 m_e
Hole effective mass 0. 4 m_e

Optical Properties

CdTe is transparent in the infrared, from close to its band gap energy (=795nm) out to wavelengths greater than 20 µm. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. The refractive index is 2. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium 649 at 10µm.

Chemical properties

CdTe has very low solubility in water. Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. It is etched by many acids including hydrochloric, and hydrobromic acid, forming (toxic) hydrogen telluride gas. Hydrochloric acid is the Solution of Hydrogen chloride ( H[[Chlorine Cl]] in water Hydrobromic Acid is formed by dissolving the diatomic molecule Hydrogen bromide in water Hydrogen telluride is the Chemical compound with the formula H 2 Te.

Cadmium telluride is commercially available as a powder, or as crystals. It can be made into nanocrystals.

Toxicity

Cadmium telluride is toxic. Toxicity is the degree to which a substance is able to damage an exposed organism It should not be ingested, nor its dust inhaled, and it should not be handled without appropriate gloves. Please refer to materials safety data sheets for details.

The toxicity is not solely due to the cadmium content. One study found that the highly reactive surface of cadmium telluride quantum dots triggers extensive reactive oxygen damage to the cell membrane, mitochondria, and cell nucleus. ^[1]

The disposal life-cycle and long term safety of cadmium telleride could become an issue in the large scale commercialization of cadmium telluride solar panels. A document hosted by the U. S. National Institutes of Health^[2] dated 2003 discloses that:

Brookhaven National Laboratory (BNL) and the U. S. Department of Energy (DOE) are nominating Cadmium Telluride (CdTe) for inclusion in the National Toxicology Program (NTP). This nomination is strongly supported by the National Renewable Energy Laboratory (NREL) and First Solar Inc. First Solar Inc is a publicly-held US energy company in the solar sector The material has the potential for widespread applications in photovoltaic energy generation that will involve extensive human interfaces. Hence, we consider that a definitive toxicological study of the effects of long-term exposure to CdTe is a necessity.

Health and Environmental Risks Researchers from the U. S. Department of Energy Brookhaven National Laboratory have found that: Large-scale use of CdTe PV modules does not present any risks to health and the environment, and recycling the modules at the end of their useful life completely resolves any environmental concerns. During their operation, these modules do not produce any pollutants, and furthermore, by displacing fossil fuels, they offer great environmental benefits. CdTe PV modules appear to be more environmentally friendly than all other current uses of Cd. ^[3]

New Theoretical Model

Making use of the authors' experimental results and the evidence available in the literature, Prof. I.M.Dharmadasa and his co-workers at Sheffield Hallam University in the United Kingdom presented an alternative theoretical model to describe the working scientific mechanism of glass/conducting glass/CdS/CdTe/metal solar cell. IM Dharmadasa is a Professor in Applied Physics and leads the Electronic Materials and Solar Energy ( Solar Cells and other Sheffield Hallam University ( SHU) is a Higher Education institution based in the South Yorkshire city of Sheffield, England The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located This model explains the behaviour of this particular solar cell in terms of a combination of a hetero-junction and a large Schottky barrier at the CdTe/metal interface. A solar cell or photovoltaic cell is a device that converts Solar energy into Electricity by the photovoltaic effect. In the article, their main experimental observations are compared with the traditionally accepted p-n junction model. A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact It is shown that the proposed model explains the experimental results more satisfactorily than the widely used p-n junction model. A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact The paper describes the guidelines to further increase the performance efficiencies based on the new model. The full article can be found here: http://www.iop.org/EJ/abstract/0268-1242/17/12/306/

References

^ Nano News - Unmodified Cadmium Telluride Quantum Dots Prove Toxic
^ http://ntp.niehs.nih.gov/ntp/htdocs/Chem_Background/ExSumPdf/CdTe.pdf
^ RENEWABLE & SUSTAINABLE ENERGY REVIEWS", Vol 8, 2004, pp 303 – 334, V M Fthenakis, “Life Cycle Impact Analysis of Cadmium in CdTe PV Production

Properties of Narrow-Gap Cadmium-Based Compounds Ed. Mercury telluride (HgTe is a binary chemical compound of mercury and Tellurium. HgCdTe or mercury Cadmium Telluride (also cadmium mercury telluride, MCT or CMT) is an Alloy of Zinc telluride is the Chemical compound with the formula ZnTe Cadmium selenide ( Cd[[Selenium Se]] is a solid binary compound of cadmium and selenium Cadmium zinc telluride, (CdZnTe or CZT, is (as the name indicates a compound of Cadmium, Zinc and Tellurium or more strictly speaking an alloy P. Capper (INSPEC, IEE, London, UK, 1994) ISBN 0-85296-880-9
D W Palmer, www.semiconductors.co.uk, 2002.06.
II-VI Infrared
Optical properties University of Reading
Material Safety data Sheet on isp optics web site (MS Word doc)
CdTe page on the web-site of the Institute of Solid State Physics of the Russian Academy of Sciences (html)

External links

© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
network: | |

Contents