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ZT-METER-870K: REALTIME MEASUREMENT
OF THE FIGURE-OF-MERIT

Developed by Fraunhofer- IPM

Frauenhofer
 
Dimension IPM-ZT-Meter-870K  
standard samples, optional sample shapes and sizes
up to 2.5cm on request.
Measurement setup  

 

Fraunhofer IPM is one of the leading research institutes in the fi eld of thermoelectrics with know-how in advanced materials research, simulation, metrology, and systems. As a specialist in thermoelectric metrology we offer an extensive support for in-house thermoelectric characterization and for turn-key, tailor-made systems development.

Thermoelectric figure of merit: ZT value

The ZT value, a dimensionless figure of merit, describes the efficiency of thermoelectric materials. It can be calculated from the so-called Seebeck coefficient (S) and the electrical (σ) and thermal conductivity (λ) of the material using the following equation, wherein the numerator S² σ  is called the power factor:

ZT= S²  σ T / λ

The parameters S, σ and λ cannot be optimized independently of one another, as heat transport and production of electrical power are reciprocally proportional. The quality factor ZT has stagnated at a value of 1 for decades; in the meantime higher ZT-values on nanostructured materials have been reported. A ZT of 1.5 would be sufficient for comercial applications. For further developments on these new materials the correct measurement of the ZT-value is important. Therefore all parameters have to be determined simultaneously and temperature dependent within one single measurement.

The Fraunhofer IPM-ZT meter

Although so-called ZT meters are available commercially for determination of the ZT value in the low and moderate temperature ranges, to date there are no suitable measuring instruments for hightemperature materials (up to 870 K).

Therefore Fraunhofer IPM has developed the first setup which allows for the determination of all parameters defining the figure-of-merit of thermoelectric materials simultaneously within one single measurement up to 870 K. In principle, the geometry is restricted to disk type samples with a diameter of 10 mm. The height of the disc is fixed to 5 mm. However, other geometries can be investigated on request.

The temperature gradient on the sample is measured by so-called differential thermocouples. This ensures a very accurate measurement of the Seebeck coefficient even at elevated temperatures. The measurement system is delivered including reference samples with known thermoelectric properties.

Specifications

Measurement range (typical)
  • Seebeck coefficient: 10 - 500 μV/K
  • electrical conductivity: 5 - 50,000 S/cm
  • thermal conductivity: 1 -15 W/mK
Measurement accuracy (typical)
  • Seebeck coefficient < ± 5%
  • electrical conductivity < ± 10%
  • thermal conductivity < ± 10%
  • figure of merit ± 25%

Options

  • measurement of customized samples
  • development of ZT meter instruments for other sample geometries
    (up to 2.5 cm)
  • variable axial mechanical stimulation

Scope of Performance

Measured material classes:

  • Skutterudites up to 820 K

  • Bi 2 Te 3 up to 520 K

  • TAGS up to 720 K

  • PbTe up to 720 K

  • Half Heuslers up to 820 K

  • FeSi up to 870 K

   
 
    Diagramm
PM-ZT-METER-870K  
Two consecutive ZT-measurements of the same sample. IPM-ZT-Meter-870K, full view.  
     
PM-ZT-METER-870K    
Measurement setup.    
     
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