PbTe – A Thermoelectric Material Heat Capacity and Thermal Conductivity

Introduction

Thermoelectric substances are promising materials for waste heat harvesting. Examples of this would be the generation of electric energy by converting the heat of automobile exhaust, or from cooling devices used in power plants. Important physical properties to consider are the so-called Seebeck coefficient (S) and Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity δ). The well-known figure of merit (Z) describes the efficiency of such materials: 

ZT = (S2 λ-1

with 

σ= DensityThe mass density is defined as the ratio between mass and volume. density 
T = temperature 

From the formula, it can be concluded that for a high Z value, the material should have a high Seebeck effect and a low Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity value. 

PbTe is a potential candidate for such applications as it has a moderate Seebeck coefficient and a relatively low Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity

1) Heat capacity (Specific Heat Capacity (cp)Heat capacity is a material-specific physical quantity, determined by the amount of heat supplied to specimen, divided by the resulting temperature increase. The specific heat capacity is related to a unit mass of the specimen.cp) values for PbTe

Results and Discussion

The specific heat of PbTe samples were measured with the NETZSCH DSC 204 F1 Phoenix® in the temperature range from RT to 300°C using the ratio method. 

Figure 1 depicts the cp curve of the PbTe sample. The specific heat values are in the range of 0.15 J/(g*K) to 0.16 J/(g*K) which is typical for this material. 

The Thermal DiffusivityThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity of PbTe was measured with the NETZSCH LFA 457 MicroFlash®. The Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity can be calculated by applying the following formula: 

λ(T) = a(T) ∙ cp(T) ∙ ρ(T) 

with 

cp = specific heat 
ρ = DensityThe mass density is defined as the ratio between mass and volume. density 
λ = Thermal DiffusivityThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity

Figure 2 shows the Thermal DiffusivityThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity, specific heat and Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity curves.

2) Thermal conductivity, Thermal DiffusivityThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity and specific heat curves of PbTe