Maximum Value Of Thermoelectric Figure Research Articles

Thermoelectric properties of cement mortar doped with steel fiber under heating conditions

In order to supply the multifunctional demand for building materials in modern construction industry, research on the thermoelectric properties of cement mortar mixed with steel fibers (diameter 0.22 mm) for engineering purposes has been carried out in this paper. The self-built thermoelectric response test system is used to collect the thermoelectric power, surface temperature and conductivity of the cement-based composite specimens in real time. Based on the comparative measurement method, the thermal conductivity of large-sized specimens was obtained. The effect of different SF content on thermal conductivity, Seebeck coefficient and ZT of the specimens were investigated. The results show that the specimens doped with steel fiber is p-type thermoelectric material, and the maximum value of thermoelectric figure of merit ZT of the cement mortar doped with 7.5 wt% steel fiber at 50℃ is 0.175. The ZT of cement mortar specimens mixed with steel fibers is relatively low, but it has good application prospects as a low-cost and widely used building material.

Theoretical prediction of thermoelectric properties of n-type binary Zintl compounds (KSb and KBi)

Although a large number of Zintl compounds have shown high thermoelectric efficiency, a very few n-type compounds are reported. Here, we use theoretical models based on Boltzmann transport formalism to determine the electrical and phonon transport properties of Potassium Antimonide (KSb) and Potassium Bismutide (KBi). Electron–phonon scattering rate is calculated based on simple model of Deformation potential and compared with the mode-dependent scattering rates by using Born approximation. The results of the two models are in good agreement. The lattice thermal conductivity is found as 0.83 Wm−1K−1 for KSb and 0.52 Wm−1K−1 for KBi at room temperature. The obtained maximum value of thermoelectric figure of merit (ZT) is 0.96 for KSb and 0.78 for KBi at 600 K by tuning the carrier concentration and temperature reveal these two n-type materials can be used as efficient thermoelectric materials.

First Principles Study of Thermoelectric Properties of Skutterudites: Ir4Sb12 and Ca0.04Ir4Sb12

First – principles calculations to study thermal and electrical properties of pristine and calcium filled skutterudite Ir4Sb12 has been carried out. Density of states (DOS) and band-structure calculations are based on Density Functional Theory (DFT) within Generalized Gradient Approximation (GGA). Transport properties are calculated using BoltzTrap software packages. Volume optimization is carried out on the basis of Murnaghan equation of states. The optimized lattice parameter of pristine Ir4Sb12 is found to be 9.4243 Å and that of calcium filled Ir4Sb12 is found to be 9.4949 Å. Our calculation shows that pristine Ir4Sb12 is a p-type of semiconductor with a narrow PBE-GGA band gap of 0.25 eV. After filling calcium, the band gap is reduced to zero showing the metallic behavior of filled compound. Band structure, density of states, variations of electrical and thermal conductivities with temperature and Seebeck coefficient show that calcium filled Ir4Sb12 has a metallic character. At Fermi level, the maximum value of thermoelectric figure of merit of unfilled Ir4Sb12 compound at temperature 400K is found to be 0.5. At the same temperature thermoelectric figure of merit calcium filled Ca0.04Ir4Sb12 is found to be around 0.03. The maximum value of of Ca filled Ca0.04Ir4Sb12 at 1000K is computed around 0.1.

Composites of Bi2–xSbxTe3 nanocrystals and fullerene molecules for thermoelectricity

New nanocomposite thermoelectric material composed from nanocrystallites of Bi–Sb–Te alloys covered by C60 molecules has been synthesized and studied. An increase of fullerene content leads to the growth of hole concentration in p-type materials and reduction of electron concentration in n-type materials. The fullerene molecules provide additional scattering of phonons reducing lattice heat conductivity. Reduction of heat conductivity exceeds the reduction of electrical conductivity for fullerene content less than 0.5 volume % and essential enhances the thermoelectric figure of merit. The maximum value of thermoelectric figure of merit equals to 1.17 at 450K was observed in Bi0.5Sb1.5Te3 composite containing 0.5 volume % C60 molecules. The experimental results were analyzed in a frame of the model based on the Boltzmann equation. The analysis considers light and heavy electrons and holes and accounts the intervalley scattering of charge carriers. The calculations of the kinetic coefficients shows that the improvement of the thermoelectric figure of merit originates from the reduction of the lattice heat conductivity caused by fullerene molecules. The dependencies of the thermoelectric figure of merit on the acceptor concentration were calculated.

C60‐doping of nanostructured Bi–Sb–Te thermoelectrics

AbstractNew bulk nanocomposite thermoelectric materials composed from nanocrystallites of Bi–Sb–Te alloys covered by C60 molecules have been synthesized and studied. The fullerene molecules provide thermal phonons blocking and particular charge transfer in the nanocomposite. The molecules act as electron traps, and thus decrease the density of free electrons in n‐type semiconductor and generate holes in p‐type materials. The capture of electrons is not accompanied by shifts of the Raman bands in C60 spectra. The density of free charge carriers and their Hall mobility change nonmonotonically with the increase of fullerene content in Bi–Sb–Te–C60 nanocomposites. The maximum value of thermoelectric figure of merit ZT = 1.15 was obtained in p‐type nanocomposite that is 30% higher than in the undoped starting material. The observed phenomenon provides new ways for transport properties optimization of thermoelectric materials and thermoelectric devices efficiency increase.