Research On Measurement Techniques And Devices For Thermoelectric Parameters

Thermoelectric materials,which can convert heat directly into electricity by carrier transport or vice versa,have attracted more and more attention in recent years.Therefore it is very important to measure the thermoelectric parameters of these materials accurately.As two essential electrical transport parameters for thermoelectric material,both the Seebeck coefficient and electrical resistivity are related to electrical signal and can be measured integratedly.Therefore,it is very significant to study new measurement method of Seebeck coefficient and resistivity and develop the integration instrument with high accuracy.In the first part of the thesis,the measurement methods for Seebeck coefficient and resistivity have been reviewed respectively,and the proposed instrument geometries have also been discussed.Based on this foundation,we presented a new instrument scheme,with which some problems in traditional measurement methods for Seebeck coefficient can be well solved.Different from the conventional methods,the new geometry adopts a four-point configuration to measure both the Seebeck coefficient and resistivity.It is more accurate and appropriate to take the average value from the four Seebeck coefficients of different two-probe combinations as the measured sample's Seebeck coefficient result than that measured by the two-point method.It can well identify the inhomogeneity of the sample by simply comparing the four Seebeck coefficients of different probe combinations.Furthermore,the four-point configuration makes it also very convenient to measure the resistivity by using the Van der Pauw method.According to the above proposed structure and method,an electric circuit was designed for the above measurement configuration.And the circuit board of PCB was made by using software Altium Designer 14.Combined with the PCB control module tM-C8 and the data acquisition card I-7018Z,which both can communicate with PC by using the 485-UART module,the hardware circuits of Seebeck coefficient and resistivity measurements are implemented.Labview was adopted as the software development tool to program the integrating measurement system.The developed measuring system has merits of friendly interface,easy to operate and stable performance.Through the modular design,the software integrated the functions of Seebeck coefficient and resistivity measurement,data display,result save and output etc,and the measurement accuracy is also enhanced.The validity of this measurement system has been verified with both the constantan alloy and p-type Bi₂Te₃ semiconductor samples,and the measurement results are in good agreement with those measured by commercial available equipment.To verify the advantage of this method in measuring the Seebeck coefficient of the inhomogeneous sample,we drilled a rectangular hole in the same p-type Bi₂Te₃ sample,filled the hole with solder by using a soldering gun.Taking the same Seebeck measurement procedure,the final result shows that the four Seebeck coefficients are different,and the new method is proved to be more accurate and effective.