Value Of Thermoelectric Figure Research Articles

Improving the Thermoelectric Properties of the Material and Increasing the Efficiency of Conversion Processes

The area of practical application of thermoelectric materials depends on the value of the thermoelectric figure of merit. The use of semiconductor materials makes it possible to realize the conditions under which the ratio of their parameters ensures the achievement of high values of thermoelectric figure of merit. The achievement of the maximum thermoelectric figure of merit causes an increase in the efficiency of conversion processes due to the improvement of the thermoelectric properties of the material. The position of the maximum value of the thermoelectric figure of merit is predetermined by the scattering parameters and the ratio of the mobilities and effective masses of charge carriers. The nature of the change in electrical conductivity is determined by the behavior of the concentration of charge carriers. Thermal conductivity, like electrical conductivity, is proportional to the concentration of electrons and the mean free path. An increase in thermoelectric efficiency is achieved by optimizing thermoelectric parameters by doping and improving the properties of com¬pounds, which leads to an optimization of the concentration of charge carriers, a change in the density of states, and a decrease in the phonon component of thermal conductivity. The improvement of the thermoelectric properties of the material and the increase in the efficiency of the conversion processes are provided at a certain concentration of charge carriers, which corresponds to the optimal value.

Дефекты межслоевой поверхности и термоэлектрические свойства в слоистых пленках топологических изоляторов n-Bi-=SUB=-2-=/SUB=-Te-=SUB=-2.7-=/SUB=-Se-=SUB=-0.15-=/SUB=-S-=SUB=-0.15-=/SUB=-

Interlayer surface defects and thermoelectric properties in layered films of n-Bi2Te2.7Se0.15S0.15 topological insulators L. N. Lukyanova*, O. A. Usov, M. P. Volkov, V. A. Rusakov Ioffe Institute Russian academy of science, 194021 St.Petersburg, Russia *E-mail: lidia.lukyanova@mail.ioffe.ru Abstract In layered films of n-Bi2Te2.7Se0.15S0.15 topological insulators optimized for temperatures below room temperature, the morphology of the (0001) interlayer surface and thermoelectric properties were studied. On the profiles of the (0001) surface, we identified neutral impurity defects arising from the substitution of Se and S atoms for Te atoms and donor antisite defects of tellurium at bismuth sites, which affect the thermoelectric properties. The average value of thermoelectric figure of merit in n-Bi2Te2.7Se0.15S0.15 films increases to <Z> ≈ 3.0•10-3 K-1 in the range 80 – 215 K, while in bulk solid solution <Z> ≈ 2.0•10-3 K-1. An increase in the thermoelectric figure of merit in films is associated with an increase in the energy dependence of the relaxation time due to an increase in the effective scattering parameter reff. It is shown that in films the Seebeck coefficient, the density of states effective mass m/m0, and the material parameter proportional to the power factor increase, while the lattice κL and electronic thermal conductivity κe decrease, which determines the increase in thermoelectric figure of merit.

The use of materials based on Si3N4 in the composition of composites for the design of high-temperature thermoelectric generators

The possibility of reducing the thermal conductivity of silicon nitride as a basis of high-temperature electrical converters was investigated in the thesis. Also, the values of thermoelectric figure of merit and efficiency of thermoelectric current generator for the case of refractory oxygen-free composites were simulated. During the study, the dependence between the m coefficient, which determines the maximum possible efficiency of the thermoelectric generator and the ZT thermoelectric figure of merit, was determined. It was shown that the coefficient of thermal conductivity of the studied materials ranges from 1,2 to 4·106 m2/s and is characterized by a negative temperature coefficient over the entire temperature range. It was found that the thermal conductivity of Si3N4-based materials varies from 2,1 to 5,1 W/(m·K) depending on the type of sintering activator. The use of Al2O3 as an activator makes it possible to obtain a 25% lower thermal conductivity value comparing to materials with the addition of MgO. For the first time, it was proved that currently it is not possible to achieve an efficiency of 0,5hT in Si3N4-based materials used as a composite basis for high-temperature thermoelectric generators development.

Synthesis and Properties of Highly Efficient Thermoelectric Materials Based on Lead Telluride with Antimony and Silver Impurity

The paper presents the results of research of X-ray diffraction and thermoelectric parameters (thermoelectric coefficient α, electrical conductivity σ and thermal conductivity coefficient k) of materials based on Lead Telluride: PbTe, PbTe:Sb, PbTe-Sb2Te3, Pb18Ag1Sb1Te20, Pb18Ag2Te20 and PbTe-Ag2Te. Established that the highest values of thermoelectric figure of merit have samples of PbTe:Sb (0,3 at.%) and system Pb18Ag1Sb1Te20, Pb18Ag2Te20. For PbTe:Sb is due to a significant increase of the electrical conductivity. For the other two materials is due to a increase the thermoelectric coefficient and a significant decrease of thermal conductivity compared to pure PbTe.

High-temperature thermoelectric properties of the sintered Bi2Sr2Ca1-xYxCu2Oy (x=0-1)

Electrical conductivity and Seebeck coefficient were measured in a temperature range of 320–1073 K for sintered samples of Bi2Sr2Ca1 − xYxCu2Oy (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). It has been found that the conduction behavior changes from n-type metallic to p-type semiconducting with increasing yttrium concentration. The power factors were in a range of 1.7–3.0 × 10−5 Wm−1 K−2 for the sample with x = 0.8, being maximized by the optimization of the yttrium concentration. The thermal conductivity for the sample with x = 0.8 was 0.73 Wm−1 K−1 at 310 K, and decreased with increasing temperature. The values of thermoelectric figure of merit were estimated to be in a range of 3.4–4.8 × 10−5 K−1 at temperatures of 320–673 K for the sample with x = 0.8.