Reliability of Thermal Conductivity Measured by Harman Method

1998 ◽  
Vol 545 ◽  
Author(s):  
Y. Shinohara ◽  
Y. Imai ◽  
Y. Isoda ◽  
I. A. Nishida
Keyword(s):  
Thermal Conductivity ◽  
Temperature Difference ◽  
Electron Concentration ◽  
Thermoelectric Materials ◽  
Comparative Method ◽  
Sintered Compact ◽  
Heat Temperature ◽  
Harman Method ◽  
Highly Sensitive ◽  
Standard Value

AbstractThe Harman method was applied to measure thermal conductivity κ of thermoelectric materials, and the reliability of the measured κ was investigated. The quantitative κ requires a highly sensitive technique to measure minute Peltier heat. Temperature difference by Peltier heat pumping was successfully measured by developing the DC method of resistance measurement. κ of n-type Bi2Te3 sintered compact and n-type PbTe boules was measured at 295K by the Harman method. Static comparative method was also applied to obtain the standard value of κ. In the case of Bi2Te3, the κ by the Harman method agreed well with the standard value. In the case of PbTe in the electron concentration ne range <5 × 1024/m3, the κ almost agreed with the standard value. However, PbTe in the ne range ≥1 × 1025/m3 showed a larger κ than the standard value. The Harman method has an error to give the larger κ for the material with a large carrier component κ, of κ This error is due to the fast conduction of Peltier heat by the carrier. The reliable κ can be measured for the material with a small κ,.

COMPARISON OF HARMAN AND COOLING COUPLE METHODS FOR Z DETERMINATION

1966 ◽  
Vol 44 (5) ◽  
pp. 971-985 ◽  
Author(s):  
W. B. Muir
Keyword(s):  
Thermal Conductivity ◽  
Electrical Resistivity ◽  
Temperature Difference ◽  
Thermoelectric Materials ◽  
Figure Of Merit ◽  
Maximum Temperature ◽  
Maximum Temperature Difference ◽  
Type Apparatus

A Peltier–Seebeck or Harman type apparatus has been constructed to measure the Seebeclc coefficient, α, thermal conductivity, κ, electrical resistivity, ρ, and the figure of merit, Z, of thermoelectric materials over the range of temperature 150–300 °K while maintaining the sample in an approximately isothermal environment. Errors in the measured values of ρ, Z, α, and κ have been kept within 1, 1.5, 3, and 5% respectively. A comparison of the maximum temperature difference, ΔTmax, measured in a cooling test and the value of ΔTmax calculated from the values of α, κ, and ρ as a function of temperature measured in the Harman apparatus shows that, for five thermocouples, agreement is obtained within 1.2 °K on the average, with the greatest disparity being 2.5 °K.

scholarly journals The origin of the lattice thermal conductivity enhancement at the ferroelectric phase transition in GeTe

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Đorđe Dangić ◽  
Olle Hellman ◽  
Stephen Fahy ◽  
Ivana Savić
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Phase Transitions ◽  
Thermoelectric Materials ◽  
Ferroelectric Phase Transition ◽  
Lattice Thermal Conductivity ◽  
Ferroelectric Phase ◽  
Structural Phase ◽  
High Symmetry ◽  
Structural Phase Transitions

AbstractThe proximity to structural phase transitions in IV-VI thermoelectric materials is one of the main reasons for their large phonon anharmonicity and intrinsically low lattice thermal conductivity κ. However, the κ of GeTe increases at the ferroelectric phase transition near 700 K. Using first-principles calculations with the temperature dependent effective potential method, we show that this rise in κ is the consequence of negative thermal expansion in the rhombohedral phase and increase in the phonon lifetimes in the high-symmetry phase. Strong anharmonicity near the phase transition induces non-Lorentzian shapes of the phonon power spectra. To account for these effects, we implement a method of calculating κ based on the Green-Kubo approach and find that the Boltzmann transport equation underestimates κ near the phase transition. Our findings elucidate the influence of structural phase transitions on κ and provide guidance for design of better thermoelectric materials.

Investigation of Thermoelectric Materials: Substitution effect of Bi on the Ag1-xPb18MTe20 (M = Sb, Bi) (x = 0, 0.14, 0.3)

2007 ◽  
Vol 1044 ◽  
Author(s):  
Mi-kyung Han ◽  
Huijun Kong ◽  
Ctirad Uher ◽  
Mercouri G Kanatzidis
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Seebeck Coefficient ◽  
Thermoelectric Materials ◽  
Figure Of Merit ◽  
Lattice Thermal Conductivity ◽  
Substitution Effect ◽  
Dimensionless Figure Of Merit ◽  
The Matrix ◽  
Mass Fluctuation

AbstractWe performed comparative investigations of the Ag1-xPb18MTe20 (M = Bi, Sb) (x = 0, 0.14, 0.3) system to better understand the roles of Sb and Bi on the thermoelectric properties. In both systems, the electrical conductivity nearly keeps the same values, while the Seebeck coefficient decreases dramatically in going from Sb to Bi. Compared to the lattice thermal conductivity of PbTe, that of AgPb18BiTe20 is substantially reduced. The lattice thermal conductivity of the Bi analog, however, is higher than that of AgPb18SbTe20 and this is attributed largely to the decrease in the degree of mass fluctuation between the nanostructures and the matrix (for the Bi analog). As a result the dimensionless figure of merit ZT of Ag1-xPb18MTe20 (M = Bi) is found to be smaller than that of Ag1-xPb18MTe20 (M = Sb).

Intrinsically Low Lattice Thermal Conductivity in Natural Superlattice (Bi2)m(Bi2Te3)n Thermoelectric Materials

2021 ◽  
Vol 33 (4) ◽  
pp. 1140-1148
Author(s):  
Hao Zhu ◽  
Chenchen Zhao ◽  
Pengfei Nan ◽  
Xiao-ming Jiang ◽  
Jiyin Zhao ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermoelectric Materials ◽  
Lattice Thermal Conductivity ◽  
Natural Superlattice

scholarly journals Enhancement of the Thermal Performance of the Paraffin-Based Microcapsules Intended for Textile Applications

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1120
Author(s):  
Virginija Skurkyte-Papieviene ◽  
Ausra Abraitiene ◽  
Audrone Sankauskaite ◽  
Vitalija Rubeziene ◽  
Julija Baltusnikaite-Guzaitiene
Keyword(s):  
Thermal Conductivity ◽  
Thermal Performance ◽  
Comparative Method ◽  
Multiwall Carbon Nanotubes ◽  
Acrylic Resin ◽  
Positive Influence ◽  
Outer Shell ◽  
Ir Camera ◽  
Spacer Fabric ◽  
Thermally Conductive

Phase changing materials (PCMs) microcapsules MPCM32D, consisting of a polymeric melamine-formaldehyde (MF) resin shell surrounding a paraffin core (melting point: 30–32 °C), have been modified by introducing thermally conductive additives on their outer shell surface. As additives, multiwall carbon nanotubes (MWCNTs) and poly (3,4-ethylenedioxyoxythiophene) poly (styrene sulphonate) (PEDOT: PSS) were used in different parts by weight (1 wt.%, 5 wt.%, and 10 wt.%). The main aim of this modification—to enhance the thermal performance of the microencapsulated PCMs intended for textile applications. The morphologic analysis of the newly formed coating of MWCNTs or PEDOT: PSS microcapsules shell was observed by SEM. The heat storage and release capacity were evaluated by changing microcapsules MPCM32D shell modification. In order to evaluate the influence of the modified MF outer shell on the thermal properties of paraffin PCM, a thermal conductivity coefficient (λ) of these unmodified and shell-modified microcapsules was also measured by the comparative method. Based on the identified optimal parameters of the thermal performance of the tested PCM microcapsules, a 3D warp-knitted spacer fabric from PET was treated with a composition containing 5 wt.% MWCNTs or 5 wt.% PEDOT: PSS shell-modified microcapsules MPCM32D and acrylic resin binder. To assess the dynamic thermal behaviour of the treated fabric samples, an IR heating source and IR camera were used. The fabric with 5 wt.% MWCNTs or 5 wt.% PEDOT: PSS in shell-modified paraffin microcapsules MPCM32D revealed much faster heating and significantly slower cooling compared to the fabric treated with the unmodified ones. The thermal conductivity of the investigated fabric samples with modified microcapsules MPCM32D has been improved in comparison to the fabric samples with unmodified ones. That confirms the positive influence of using thermally conductive enhancing additives for the heat transfer rate within the textile sample containing these modified paraffin PCM microcapsules.

scholarly journals Thermoelectric Materials for Textile Applications

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3154
Author(s):  
Kony Chatterjee ◽  
Tushar K. Ghosh
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Seebeck Coefficient ◽  
Thermoelectric Materials ◽  
Figure Of Merit ◽  
Inorganic Materials ◽  
Peltier Effect ◽  
Electronic Textiles ◽  
Heating And Cooling ◽  
Recent Attention

Since prehistoric times, textiles have served an important role–providing necessary protection and comfort. Recently, the rise of electronic textiles (e-textiles) as part of the larger efforts to develop smart textiles, has paved the way for enhancing textile functionalities including sensing, energy harvesting, and active heating and cooling. Recent attention has focused on the integration of thermoelectric (TE) functionalities into textiles—making fabrics capable of either converting body heating into electricity (Seebeck effect) or conversely using electricity to provide next-to-skin heating/cooling (Peltier effect). Various TE materials have been explored, classified broadly into (i) inorganic, (ii) organic, and (iii) hybrid organic-inorganic. TE figure-of-merit (ZT) is commonly used to correlate Seebeck coefficient, electrical and thermal conductivity. For textiles, it is important to think of appropriate materials not just in terms of ZT, but also whether they are flexible, conformable, and easily processable. Commercial TEs usually compromise rigid, sometimes toxic, inorganic materials such as bismuth and lead. For textiles, organic and hybrid TE materials are more appropriate. Carbon-based TE materials have been especially attractive since graphene and carbon nanotubes have excellent transport properties with easy modifications to create TE materials with high ZT and textile compatibility. This review focuses on flexible TE materials and their integration into textiles.

Metal phosphide CuP2 as a promising thermoelectric material: an insight from first-principles study

2021 ◽  
Author(s):  
Un-Gi Jong ◽  
Chol-Hyok Ri ◽  
Chol-Jin Pak ◽  
Chol-Hyok Kim ◽  
Stefaan Cottenier ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermoelectric Material ◽  
Thermoelectric Materials ◽  
First Principles ◽  
Lattice Thermal Conductivity ◽  
Metal Phosphide ◽  
First Principles Study ◽  
Metal Phosphides ◽  
Large Lattice

In the search for better thermoelectric materials, metal phosphides have not been considered to be viable candidates so far, due to their large lattice thermal conductivity. Here we study thermoelectric...

Electronic Structure and Transport Properties of La2Zr2O7 Pyrochlore from First Principles

2018 ◽  
Vol 281 ◽  
pp. 767-773
Author(s):  
Zheng Li ◽  
Wei Pan
Keyword(s):  
Thermal Conductivity ◽  
Transport Properties ◽  
Electron Concentration ◽  
Boltzmann Transport ◽  
Principle Calculation ◽  
First Principle Calculation ◽  
Electronic Thermal Conductivity ◽  
Transport Calculation ◽  
Scattering Time ◽  
High Temperature Electronic

The first principle calculation as well as the Boltzmann transport calculation have been employed to study the high temperature electronic transport properties of pyrochlore La2Zr2O7. Combing constant scattering time approximation and experiment data, the electronic thermal conductivity and electron concentration are calculated as a function of temperature. The electronic thermal conductivity is 2.6×10-4 W/(m.s) at 1270K and 7.2×10-3 W/(m.s) at 1770K. The electron concentration increase rapidly with when the temperature is above 1600K.

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