Materials of Interest showing high thermoelectric behavior: 3.1. Bismuth chalcogenides and their nanostructures Materials such as Bi2Te3 and Bi2Se3 comprise some of the best performing room temperature thermoelectrics with a temperature-independent thermoelectric effect, ZT, between 0.8 and 1.0. Nanostructuring these materials to produce a layered super lattice structure of alternating Bi2Te3 and Bi2Se3 layers produces a device within which there is good electrical conductivity but perpendicular to which thermal conductivity is poor. The result is an enhanced ZT (approximately 2.4 at room temperature for p-type). 3.2. Magnesium group IV compounds Mg2BIV (BIV = Si, Ge, Sn) compounds and their solid solutions are good thermoelectric materials …show more content…
These materials possess relatively good electrical properties while maintaining very low thermal conductivities.
3.3. Skutterudites
The physical properties of skutterudites depend sensitively on their compositions. As depicted in figure 5, the linked octahedra produce a void, or vacant site, at the center of the (TX6)8 cluster, occupying a body-centered position in the cubic lattice. This is a large void that can accommodate relatively large metal atoms, resulting in the formation of filled skutterudites. Many different elements have been introduced into the voids of skutterudites, including lanthanide, alkaline-earth, alkali and Group IV elements.
Figure 5. Schematic illustration of a skutterudite crystal, where the guest atom is inside a 12-coordinated “cage” (green) surrounded by yellow pnicogen (family of Bi, Sb, As, P, or N) atoms. The metal sites are depicted in
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CsBi4Te6 is very responsive to the type and level of doping agent used. Low doping levels significantly affect the charge transport properties of CsBi4Te6. Appropriate p-type doping of CsBi4Te6 with SbI3 or Sb gives rise to a high ZT max of 0.8 at 225 K.
3.8. Nanostructured thermoelectric Materials:
Several nanostructured thermoelectric materials have been developed so far, some of them are; 2D thermoelectric nanomaterials: quantum wells and superlattices, 1D thermoelectric nanomaterials: nanowires, Nanocomposites: Bi2Te3-basednanocomposites. Bi2Te3 and their related nanocomposites, the best thermoelectric materials at room temperature, are extensively used for the first thermoelectric devices for commercial Peltier elements.
A polycrystalline p-type Bi0.5 Sb1.5 Te3 bulk nanocomposite fabricated by hot pressing of ball-milled nanopowders, exhibited ZT of 1.2 at room temperature and ZT of 1.4 at 373K, SiGe-based nanocomposites: a significant improvement in ZT was achieved in p-type SiGe nanocomposites, with a peak value about 0.95 at 1173–1223 K through ball milling and hot-pressing
Here (Figure 1), we can see the crystalline structure of potassium feldspar (KAlSi3O8), which consists of corners that share AlO4 and SiO4 tetrahedrons. These tetrahedrons contain either an aluminum or a silicon atom, each connected to four oxygen atoms, and also there are relatively large potassium cations that reside on junctions within the framework.
Barium titanate is chemical compound with formula (BaTiO3) ,has perovskite structure (a group of crystalline material take it name from natural mineral perovskite (CaTiO3) with typical formula ABO3.[35] In barium titanate, (Ba:A) ion has large size (r=1.35 A), it located at the corner of unit cell and it is encompassed by (12) oxygen ion, oxygen are bound to both cation and it located at the center cubic face. While (Ti:B) are small in size (r=0.68 A), occupy the center of unit cell and are surrounded by (6) oxygen ion forming a octahedral site( TiO6). Barium titanate is formed by linking the corners of (TiO6) formed large dodecahedron hole with Ba+2 are fit at the center of the hole.[36]
Figure 2 shows the isothermal entropy changes heating the sample (a), (b) and (c) and (the figure 3 cooling the sample (a), (b) and (c)). The solid curves are due to the variations from atmospheric pressure (P^at) to applied pressure, P=1.5 kbar (fig.2a and fig.3a), P=2.0 kbar (fig.2b and fig.3b), P=2.9 kbar (fig.2c and fig.3c) without applied magnetic field (µ_0 h_0=0 T) for sample heating and cooling, as indicated by the arrows. The open circles and open squares represent 〖ΔS〗_T vs. T experimental data for Gd5Si2Ge2 which are in good agreement with our theoretical curves for sample heating and cooling, respectively [19]. The value was used for this compound in our theoretical curves [28], value that we kept in our model in all theoretical curves. For all pressure changes, th...
surface peak [20], which can be attributed to the reduction in coordination of Fe (i.e. in hexaferrite, Fe is present in five nonequivalent crystallographic sites, three octahedral, one tetrahedral
File:Potassium.jpg. N.d. Wikimedia Commons. Web. 22 Apr. 2014. (This source is credible because it is a picture of potassium that I found).
The molar specific heats of most solids at room temperature and above are nearly constant, in agreement with the Law of Dulong and Petit. At lower temperatures the specific heats drop as quantum processes become significant. The Einstein-Debye model of specific heat describes the low temperature behavior.
An experiment was conducted at the Materials Research Laboratory, at Pennsylvania State University, University Park utilizing a multi ion beam technique to deposit PZT on various unheated substrates. In the experiment a multi ion beam sputtering system was utilized to sputter PZT from separate metals of Pb, Zr, and Ti. This system provides uniformity over large areas, and control over stoichiometry since PZT was broken into single elemental compounds. In the experiment the three metals targets, Pb, Zr, and Ti were placed on adjustable brackets. The brackets were designed to be flexible and adjustable so that they could be placed in any position with respect to the ion beam. Three primary ion sources were focused and adjusted with respect to the targets. The targets were placed a distance of about 11 to 16 cm from the ion source and a shutter was pla...
direct conversion of heat into electric energy, or vice versa. The term is generally restricted to the irreversible conversion of electricity into heat described by the English physicist James P. Joule and to three reversible effects named for Seebeck, Peltier, and Thomson, their respective discoverers. According to Joule’s law, a conductor carrying a current generates heat at a rate proportional to the product of the resistance (R) of the conductor and the square of the current (I). The German physicist Thomas J. Seebeck discovered in the 1820s that if a closed loop is formed by joining the ends of two strips of dissimilar metals and the two junctions of the metals are at different temperatures, an electromotive force, or voltage, arises that is proportional to the temperature difference between the junctions. A circuit of this type is called a thermocouple; a number of thermocouples connected in series is called a thermopile. In 1834 the French physicist Jean C. A. Peltier discovered an effect inverse to the Seebeck effect: If a current passes through a thermocouple, the temperature of one junction increases and the temperature of the other decreases, so that heat is transferred from one junction to the other. The rate of heat transfer is proportional to the current and the direction of transfer is reversed if the current is reversed. The Scottish scientist William Thomson (later Lord Kelvin) discovered in 1854 that if a temperature difference exists between any two points of a current-carrying conductor, heat is either evolved or absorbed depending upon the material. (This heat is not the same as Joule heat, or I2R heat, which is always evolved.) If heat is absorbed by such a circuit, then heat may be evolved if the direction of the current or of the temperature gradient is reversed.
Nano-thermal analysis methods are also known as micro-thermal procedures and they use the principle of characterizing highly localized materials on a micrometer. The characterization is then changed from a micrometer scale to a sub-micrometer scale with the temperature being regulated to the specified units. The application of nano-thermal analysis methods started towards the end of the 20th century. Although it has been applied in several other fields including microelectronics, its application in pharmaceuticals has not been that popular.
23. S. Alwarappan, S. Boyapalle, A. Kumar, C.-Z. Li and S. Mohapatra, J. Phys. Chem. C, 2012, 116, 6556–6559
Crystal Structures are divided into seven systems called lattices. A lattice is the arrangement of points of the atoms, ions, or molecules composing a crystal are centered at. The seven systems crystals are divided into consist of Cubic, Tetragonal, Orthorhombic, Hexagonal, Trigonal, Triclinic, and Monoclinic. The Cubic system is fairly basic. It consists of one lattice point on each corner of the cube, which each lattice point shared equally between eight adjacent cubes. The Tetragonal system is similar to the cubic crystals, but it is longer along one axis. Tetragonal crystal lattices form when stretching has occurred along one lattice vector. As a result, the cube is turned into a rectangular prism with a square base. The Orthorhombic system is like the Tetragonal crystals, but it does not have a square in the cross section. This lattice is formed when stretching has occurred along two lattice vectors, which fo...
Inorganic nanowires often exhibit unique property that is useful for future applications. As the sizes of materials are decreasing down to the nanoscale level, the physical structure and chemical properties of nanomaterials are also diverging away from its bulk form [N&N]. Nanowires display the quantum confinement effect which describes the energy level of electrons as discrete unit [N&N]. For example, the transfer of electrons from the valence band to the conducting band requires a specific amount of energy [N&N]. Additionally, the surface area to volume ratio increases as the particles gets smaller [N&N]. This property supports many of the future application of TiO2 nanowires that requires a large surface a...
This is a technique to study structural details of the samples. By this technique size and shape of the crystal , the average atomic spacing , orientation of the single and ploy crystal are determined.
Advanced materials are classified as completely new materials which have some specific properties and functions. These advance materials have large utility in daily life, hospitality, industries, sports etc. currently scientists and researchers are working and studying their specific functions etc. some great examples of these materials include thin membranes, Composite and hybrid materials, polymers, ceramic and radiation shielding composites; lightweight and nanocomposite, Metals and alloys, Ceramics, Smart materials (Photo-, thermo-, piezo-, tribo- and electro-chromic materials. Thin film coatings. Now a day thermoelectric materials have significant value in scientific world it include temperature measuring devices in furnace, energy harvestings and advance sensor etc. and many more. Here we discuss about thermoelectric and materials used in it.
Dielectric parameters measured in the frequency range of 10Hz to 10MHz at room temperature were shown in respective figures. The measure of the ability to store electric charge is called as Dielectric constant. Figure_____ shows the variation of dielectric constant with frequency. It is evident from the figure that with increase in frequency, the dielectric constant has decreased and finally attains constant value at higher frequency. The decrease in dielectric constant in lower frequency region is very fast and becomes slow with increase in frequency. Dielectric constant of ferrites depends upon the conduction process. The fact responsible for this conduction is hopping of electron between Fe2+ and Fe3+ . The polarization observed at grain boundaries due to local charge displacement is mainly due to this hopping of electrton. Such variation of dielectric constant with frequency in ferrites can be explained by Maxwell-Wagner model [16]. According to this model, the dielectric structure of a ferrite material is a combination of two layers. The first layer consists of large ferrite grains and acts as a conductive layer, the other with the grain boundaries that are poor conductors (offer high resistance). By hopping, the electrons heap up at the grain boundaries due to high resistance and results in polarization. This hopping