JP7232513B2 - Seebeck coefficient measuring device and its measuring method - Google Patents

Description

The present invention relates to an apparatus and method for measuring the Seebeck coefficient, which is a performance index of thermoelectric conversion, and more particularly to an apparatus and method for measuring the Seebeck coefficient near the center in the thickness direction of a plate-shaped sample.

Thermoelectric elements are known that convert thermal energy into electrical energy using Seebeck effect, Peltier effect, Thomson effect, and the like. By using such a thermoelectric element, electric power can be obtained from various unused heat sources such as factory waste heat and automobile combustion engine waste heat, and a new electric power source can be easily obtained without power. In one of the property evaluations of thermoelectric materials used in such thermoelectric elements, the Seebeck coefficient, which is a performance index of thermoelectric conversion, is measured. In general, the Seebeck coefficient S=ΔV/ΔT is calculated by measuring the electromotive force ΔV generated between both ends of the sample to be measured while measuring the temperature ΔT at both ends.

Patent Literature 1 discloses a method of determining the Seebeck coefficient by attaching two Peltier elements directly to an object to be measured to give a temperature difference without cutting out a sample for measurement from a large object to be measured. Here, copper electrodes are brought into contact with both end surfaces of an object to be measured as an ingot, Peltier elements are brought into contact with and fixed to the outside thereof, and temperature sensing parts of thermocouples are brought into contact with a plurality of measurement points of the object to be measured. there is Then, with one Peltier element on the heat-generating side and the other Peltier element on the heat-absorbing side, a current is passed through the object to be measured, and the temperature at the measurement point and the thermoelectromotive force between the measurement points are measured to obtain the Seebeck coefficient.

Thermoelectric elements in the form of thin plates have been proposed. When obtaining the Seebeck coefficient of such a plate-like body, it is possible to give a temperature difference (thermal gradient) in the in-plane direction of the plate-like body and measure the electromotive force. On the other hand, when the plate-like body has anisotropy, especially in the thickness direction, and when trying to obtain the Seebeck coefficient based on the thermal anisotropy in this direction, the temperature gradient is It is necessary to measure the electromotive force by applying it in the thickness direction of the plate-like body.

For example, Patent Literature 2 discloses a method of determining the Seebeck coefficient in the thickness direction of a conductive thin film of metal, semiconductor, or the like. Here, the temperature difference in the thickness direction is first calculated from the amount of heat given to the conductive thin film made of a silicon wafer by AC heating and the thermal conductivity of the conductive thin film. Then, the Seebeck coefficient can be calculated from the potential difference measured with respect to the temperature difference.

Japanese Patent Application Laid-Open No. 2004-22912 JP-A-2000-74862

As described above, when trying to obtain the Seebeck coefficient in the thickness direction of a plate-like sample, it is necessary to apply a temperature gradient in the thickness direction of the plate-like sample and measure the electromotive force. However, it is difficult to control such a temperature gradient, and in particular, for a thin plate with a smaller thickness, for example, a plate-like (thin-film) sample with a thickness of about 100 μm or less, it is necessary to It is difficult to stably form a sufficient temperature difference. On the other hand, conductive polymers such as PEDOT/PSS, which have been attracting attention in recent years, are often formed into films with a small thickness. I have a problem.

The present invention has been made in view of such circumstances, and its object is to provide a measuring apparatus and a measuring method capable of accurately measuring the Seebeck coefficient near the center in the thickness direction of a plate-shaped sample. That's what it is.

In the method for measuring the Seebeck coefficient near the center in the thickness direction of a plate-shaped sample according to the present invention, the plate-shaped sample is placed between a high temperature side variable heat source and a low temperature side variable heat source that are arranged opposite to each other and can be independently temperature-controlled. The temperature of the high-temperature side variable heat source and the low-temperature side variable heat source is increased and decreased by the same temperature to obtain the temperature difference in the thickness direction of the plate-shaped sample, and then the electromotive force is measured. The Seebeck coefficient is repeatedly calculated from the relationship between the temperature difference and the electromotive force.

Further, the apparatus for measuring the Seebeck coefficient near the center in the thickness direction of a plate-shaped sample according to the present invention comprises a high temperature side variable heat source and a low temperature side variable heat source which are arranged opposite to each other and whose temperatures can be independently controlled; a measurement unit that sandwiches the plate-shaped sample between the low-temperature side variable heat source and measures the electromotive force of the plate-shaped sample in the thickness direction, wherein the measurement unit includes the high temperature side variable heat source and the low temperature side. The temperature of the variable heat source is increased and decreased by the same temperature to obtain the temperature difference in the thickness direction of the plate-shaped sample, and then the electromotive force is measured. It is characterized by calculating the Seebeck coefficient from the relationship.

According to this invention, the temperatures of the high temperature side variable heat source and the low temperature side variable heat source are increased and decreased by equal temperatures to give a temperature difference in the thickness direction of the plate-shaped sample, and then the electromotive force is measured sequentially, It is possible to measure the electromotive force while keeping the temperature constant on the half-thickness surface of the plate-shaped sample. can be changed to measure the Seebeck coefficient in the vicinity of the center in the thickness direction even for a thin plate-shaped sample.

In the invention described above, the calculation may be performed with the electromotive force set to zero when the temperature difference is zero. According to this invention, the Seebeck coefficient near the center in the thickness direction of the plate-shaped sample can be measured with high accuracy and efficiency.

In the invention described above, the electromotive force is measured using two thermocouples interposed between the plate-shaped sample and the high-temperature side variable heat source and the low-temperature side variable heat source, respectively. good too. Further, the high temperature side variable heat source and the low temperature side variable heat source may be Peltier elements. According to this invention, the Seebeck coefficient in the vicinity of the center in the thickness direction of the plate-like sample can be accurately and easily measured.

1 is a measuring device according to the invention; It is a figure which shows the principle of this invention. 4 is a graph illustrating the principle of the invention; 4 is a graph showing the relationship between the temperature difference of the heat source and the electromotive force in the thickness direction of the plate-shaped sample (nickel plate) measured by the measuring device according to the present invention. 4 is a graph showing the relationship of the electromotive force in the thickness direction of a plate-like sample (PEDOT/PSS) with respect to the temperature difference of the heat source measured by the measuring device according to the present invention. It is a figure which shows the application example of this invention.

The present inventors have found a method capable of forming a necessary and sufficient temperature difference for measuring thermoelectric properties in the thickness direction of a film-like sample including a conductive polymer such as PEDOT/PSS. In other words, in organic thermoelectric materials, which have lower thermal conductivity than inorganic (metallic) thermoelectric materials, even if the thickness of the sample is thin, it is possible to form a temperature gradient that can be regarded as linear inside, and as a result, thermoelectric properties are improved. Accurate evaluation is possible.

A Seebeck coefficient measuring apparatus, which is one embodiment of the present invention, will be described in detail below with reference to the drawings.

As shown in FIGS. 1 and 2, an apparatus 1 for measuring the Seebeck coefficient near the center in the thickness direction of a plate-shaped sample 10 includes a high temperature side variable heat source 5 and a low temperature side variable heat source 5 which are arranged opposite to each other and whose temperatures can be independently controlled. including 6.

The high-temperature-side variable heat source 5 and the low-temperature-side variable heat source 6 have heat capacities larger than those of the plate-like sample 10, and are in thermal contact with the respective main surfaces of the plate-like sample 10 so as to control their temperatures. A heater or cooler, preferably a Peltier element whose temperature can be electrically controlled. As will be described later, in the measurement of the organic thermoelectric material, the operating temperature range is from room temperature to about 200° C., so a Peltier element is particularly preferable because it has excellent temperature controllability in this temperature range.

Furthermore, the measuring device 1 sends a signal for controlling the temperature of the high temperature side variable heat source 5 and the low temperature side variable heat source 6, and at a predetermined set temperature, the thickness direction of the plate-shaped sample 10 sandwiched between them includes a measurement unit (central control unit) 30 that measures the electromotive force (voltage) V of The measurement unit 30 raises and lowers the temperature of each of the high temperature side variable heat source 5 and the low temperature side variable heat source 6 by an equal temperature ΔT, thereby setting the surface temperature of the plate-shaped sample 10 to T _H and T _L and This is intended to measure the electromotive force V in the thickness direction of the plate-like sample 10 while maintaining a constant temperature in the 1/2 thickness plane C1 (the center plane in the thickness direction).

The electromotive force V in the thickness direction of the plate-like sample 10 can be measured by known measurement means applied to both main surfaces of the plate-like sample 10 in various forms. For example, one thermocouple 12a is inserted between the plate-shaped sample 10 and the high temperature side variable heat source 5, and the other thermocouple 12b is inserted between the plate shaped sample 10 and the low temperature side variable heat source 6, and these two thermocouples It can be measured as an electromotive force between 12 identical single-sided strands.

Next, the details of the measuring method and principle of the Seebeck coefficient measuring apparatus 1 described above will be described.

First, when the high temperature side variable heat source 5 and the low temperature side variable heat source 6 have the same temperature T= _T0 , there is no temperature difference (temperature gradient) in the thickness direction of the plate-shaped sample 10, so the two thermocouples 12 measure The applied electromotive force V is zero. At this time, as shown in FIG. 3, if the temperature difference is plotted on the horizontal axis and the potential difference V is plotted on the vertical axis, the origin _S0 corresponds.

On the other hand, the measuring unit 30 raises the temperature of the high temperature side variable heat source 5 by ΔT ₁ to T _H =T ₀ +ΔT ₁ , and lowers the temperature of the low temperature side variable heat source 6 by ΔT ₁ to T _L =T ₀ -. Let ΔT be ₁ . That is, from the balance between the amount of heat input and the amount of heat extraction, the temperature at the half-thickness plane C1 at the center in the thickness direction of the plate-shaped sample 10 is constant at T= _T0 . Then, the temperatures of both principal surfaces of the plate-shaped sample 10 in contact with the high temperature side variable heat source 5 and the low temperature side variable heat source 6 change by +ΔT ₁ and −ΔT ₁ respectively, and T _H =T ₀ +ΔT ₁ and T _L =T ₀ −ΔT ₁ . In other words, the plate-like sample 10 has a temperature difference of _2ΔT1 in the thickness direction. The measurement unit 30 measures the electromotive force V= _V1 in the thickness direction of the plate-shaped sample 10 with respect to this temperature difference with the two thermocouples 12 . This time corresponds to the measurement point _S1 in FIG.

Similarly, the measuring unit 30 raises the temperature of the high-temperature side variable heat source 5 from the initial temperature T= _T0 by _ΔT2 to T _H = _T0 + _ΔT2 , and raises the temperature of the low-temperature side variable heat source 6 to Then, the temperature T is lowered by ΔT ₂ from the initial temperature T=T ₀ to give T _L =T ₀ +ΔT ₂ . At this time as well, the temperature at the 1/2 thickness plane C1 at the center in the thickness direction of the plate-shaped sample 10 is constant at T= _T0 in the same manner as described above. Then, when the electromotive force V= _V1 in the thickness direction of the plate-shaped sample 10 when a temperature difference of _2ΔT2 is given in the thickness direction is measured by two thermocouples 12, it corresponds to the measurement point _S2 in FIG. do.

By the way, since the Seebeck coefficient S is a potential difference with respect to a temperature difference, it corresponding to S ₁ and S ₂ in FIG. 3 is represented by V ₁ /2ΔT ₁ and V ₂ /2ΔT ₂ respectively. These are Seebeck coefficients S obtained at the same temperature and with varying temperature gradients in the vicinity of the center in the thickness direction of the plate-shaped sample 10, and should be the same value. That is, since V ₁ /2ΔT ₁ = _{V 2} / _{2ΔT 2} , V ₁ /V ₂ =ΔT ₁ /ΔT ₂ , and as shown in _FIG . It is above.

As described above, the temperatures of the high-temperature-side variable heat source 5 and the low-temperature-side variable heat source 6 are adjusted so as to keep the temperature constant in the vicinity of the center in the thickness direction of the plate-shaped sample 10, the half-thickness plane C1 (see FIG. 2). respectively increasing and decreasing by equal temperatures can change only the temperature gradient. When the electromotive force V in the thickness direction _of the plate-shaped sample 10 is measured in _this manner, the potential difference V is proportional to the temperature _difference . This gradient corresponds to the Seebeck coefficient near the center in the thickness direction of the plate-like sample 10 and can be calculated. By increasing the number of measurement points, the calculation error of the Seebeck coefficient can be reduced.

As described above, the temperatures of the high temperature side variable heat source 5 and the low temperature side variable heat source 6 are increased and decreased by the same temperature, respectively, and only the temperature gradient is maintained without changing the temperature near the center in the thickness direction of the plate-shaped sample. The Seebeck coefficient in the vicinity of the center in the thickness direction of the plate-like sample 10 in various forms such as sheet (film) and plate-like can be measured with high accuracy by changing and successively performing measurements a plurality of times. In particular, the thinner the thickness of the plate-shaped sample 10, the less heat enters and exits from its side surfaces, so the temperature gradient as described above can be accurately obtained, and the Seebeck coefficient near the center in the thickness direction can be accurately measured. It becomes possible.

The above-described measurement method in which only the temperature gradient is changed without changing the temperature near the center in the thickness direction of the plate-shaped sample can be applied to other than the measurement of the Seebeck coefficient.

Figure 6 shows an application to a method for measuring the thermal anisotropy of a conductive polymer film by the four-terminal method using ring electrodes (see ACS Macro Lett., 2014, 3, pp 948-952.). . That is, a pair of ring-shaped electrodes 120a and 120b are provided with the thin plate sample 110 vertically sandwiched therebetween, and a pair of disc electrodes 130a and 130b are similarly provided in the annular interior thereof with the thin plate sample 110 vertically sandwiched therebetween. At this time, by changing the distance d between the ring-shaped electrodes 120a, 120b and the disc electrodes 130a, 130b, electrical conductivity can be measured, for example.

At the same time, when the temperatures of the high-temperature side heater and the low-temperature side heater arranged above and below the thin plate sample 110 are raised and lowered by equal temperatures as described above, the temperature at the central portion in the thickness direction of the thin plate sample 110 is kept constant. , only its temperature gradient can be changed. By providing the disk electrodes 130a and 130b with thermocouples, it is possible to simultaneously measure the electric conductivity (conductivity) and the Seebeck coefficient.

Measurement examples in which the Seebeck coefficients of various plate-like materials were measured by the above-described measurement method are shown below.

FIG. 4 shows the result of measuring a thin nickel plate with a thickness of 1 mm by the method described above, with the temperature near the center in the thickness direction set to 25°C. It can be seen that a plurality of measurement points are on a straight line passing through the origin. From this relationship (the slope of the straight line), the Seebeck coefficient can be obtained as -21 μV/K. The Seebeck coefficient near the center in the thickness direction can be obtained with high accuracy even for a thin metal plate with good thermal conductivity.

FIG. 5 shows the results of measurement of a 100 μm-thick PEDOT/PSS film by the method described above, with the temperature near the center in the thickness direction set to 25°C. Again, the measurement points are on a straight line passing through the origin. From this relationship (the slope of the straight line), the Seebeck coefficient can be determined to be 16 μV/K. Even for a thin plate with strong anisotropy, the Seebeck coefficient near the center in the thickness direction can be obtained with high accuracy. In organic thin films, which generally have lower thermal conductivity than metal materials, the temperature gradient can be controlled more accurately even with thinner samples. can be measured.

Although embodiments according to the present invention have been described above, the present invention is not necessarily limited thereto, and a person skilled in the art can make various modifications without departing from the spirit of the present invention or the scope of the appended claims. Alternate embodiments and modifications may be found.

1 Measuring device 5 High temperature side variable heat source 6 Low temperature side variable heat source 10 Plate-shaped sample 12 Thermocouple 30 Measurement part C1 1/2 thickness surface

Claims (8)

A method for measuring the Seebeck coefficient near the center in the thickness direction of a plate-shaped sample, comprising:
Between a high temperature side variable heat source and a low temperature side variable heat source which are arranged opposite to each other and whose temperature can be controlled independently, a temperature difference between the high temperature side variable heat source and the low temperature side variable heat source creates a linear temperature gradient in the thickness direction. The plate-shaped sample is sandwiched so as to be formed inside , and the temperatures of the high-temperature side variable heat source and the low-temperature side variable heat source are raised and lowered by the same temperature, respectively, without changing the temperature near the center in the thickness direction. A method for measuring a Seebeck coefficient, comprising: measuring an electromotive force after changing a linear temperature gradient ; repeating this measurement; and calculating the Seebeck coefficient from the relationship between the electromotive force and the temperature difference. 2. The method of measuring the Seebeck coefficient according to claim 1, wherein when the temperature difference is zero, the electromotive force is assumed to be zero to check the accuracy of the calculation. 2. The electromotive force is measured using two thermocouples interposed between the plate-shaped sample and the high temperature side variable heat source and the low temperature side variable heat source, respectively. 2. The method for measuring the Seebeck coefficient according to 2. 4. The method for measuring the Seebeck coefficient according to claim 1, wherein the high temperature side variable heat source and the low temperature side variable heat source are Peltier elements. A device for measuring the Seebeck coefficient near the center in the thickness direction of a plate-shaped sample,
a high-temperature-side variable heat source and a low-temperature-side variable heat source which are arranged opposite to each other and whose temperatures can be independently controlled;
Between the high temperature side variable heat source and the low temperature side variable heat source, the plate-shaped heat source is formed so that a temperature difference between the high temperature side variable heat source and the low temperature side variable heat source forms a linear temperature gradient in the thickness direction. a measuring unit that sandwiches a sample and measures the electromotive force in the thickness direction of the plate-shaped sample,
The measuring unit raises and lowers the temperatures of the high-temperature-side variable heat source and the low-temperature-side variable heat source by the same temperature, respectively, to change the linear temperature gradient without changing the temperature near the center in the thickness direction. An apparatus for measuring the Seebeck coefficient, characterized in that the electromotive force is measured repeatedly in the above-described step, and the Seebeck coefficient is calculated from the relationship between the electromotive force and the temperature difference. 6. The Seebeck coefficient measuring apparatus according to claim 5, wherein when the temperature difference is zero, the electromotive force is assumed to be zero to check the accuracy of the calculation. 7. The measuring unit according to claim 5, wherein the measuring unit includes two thermocouples interposed between the plate-shaped sample and each of the high temperature side variable heat source and the low temperature side variable heat source. A device for measuring the Seebeck coefficient. 8. The Seebeck coefficient measuring apparatus according to claim 5, wherein said high temperature side variable heat source and said low temperature side variable heat source are Peltier elements.

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