Lead telluride is a compound of
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...
and
tellurium
Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...
(PbTe). It crystallizes in the NaCl crystal structure with Pb atoms occupying the cation and Te forming the anionic lattice. It is a narrow gap semiconductor with a band gap of 0.32 eV. It occurs naturally as the mineral
altaite.
Properties
*
Dielectric constant
The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulat ...
~1000.
* Electron
Effective mass ~ 0.01
''m''e
* Hole mobility, μ
p = 600 cm
2 V
−1 s
−1 (0 K); 4000 cm
2 V
−1 s
−1 (300 K)
Applications
PbTe has proven to be a very important intermediate
thermoelectric material. The performance of thermoelectric materials can be evaluated by the figure of merit,
, in which
is the
Seebeck coefficient
The Seebeck coefficient (also known as thermopower, thermoelectric power, and thermoelectric sensitivity) of a material is a measure of the magnitude of an induced thermoelectric voltage in response to a temperature difference across that material ...
,
is the
electrical conductivity
Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
and
is the
thermal conductivity
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
. In order to improve the thermoelectric performance of materials, the power factor (
) needs to be maximized and the thermal conductivity needs to be minimized.
The PbTe system can be optimized for power generation applications by improving the power factor via band engineering. It can be doped either n-type or p-type with appropriate dopants. Halogens are often used as n-type doping agents. PbCl
2, PbBr
2 and PbI
2 are commonly used to produce donor centers. Other n-type doping agents such as Bi
2Te
3, TaTe
2, MnTe
2, will substitute for Pb and create uncharged vacant Pb-sites. These vacant sites are subsequently filled by atoms from the lead excess and the valence electrons of these vacant atoms will diffuse through crystal. Common p-type doping agents are Na
2Te, K
2Te and Ag
2Te. They substitute for Te and create vacant uncharged Te sites. These sites are filled by Te atoms which are ionized to create additional positive holes. With band gap engineering, the maximum zT of PbTe has been reported to be 0.8 - 1.0 at ~650K.
Collaborations at Northwestern University boosted the zT of PbTe by significantly reducing its thermal conductivity using ‘all-scale hierarchical architecturing'. With this approach, point defects, nanoscale precipitates and mesoscale grain boundaries are introduced as effective scattering centers for
phonons
In physics, a phonon is a collective excitation in a periodic, Elasticity (physics), elastic arrangement of atoms or molecules in condensed matter physics, condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phon ...
with different mean free paths, without affecting charge carrier transport. By applying this method, the record value for zT of PbTe that has been achieved in Na doped PbTe-SrTe system is approximately 2.2.
In addition, PbTe is also often alloyed with tin to make
lead tin telluride, which is used as an
infrared detector material.
See also
*
Yellow Duckling, which used a lead telluride sensor to make the first
infrared linescan
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
camera
References
External links
National Pollutant Inventory Lead and compounds fact sheet
{{Tellurides
Tellurides
Lead(II) compounds
IV-VI semiconductors
Thermoelectricity
Rock salt crystal structure