JP7323108B2 - Thermoelectric property evaluation unit, thermoelectric property evaluation device, and thermoelectric property evaluation method - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act (1) Reason for disclosure 1 Meeting name and venue: 2018 79th Japan Society of Applied Physics Autumn Scientific Lecture Exhibition Exhibition date: September 18-21, 2018 (2 ) Reason for disclosure 2 Meeting name, Venue: 39th Japan Symposium on Thermophysical Properties Date: November 13, 2018 (3) Reason for disclosure 3 Meeting name, Venue: 39th Japan Symposium on Thermophysical Properties Exhibition corner Exhibition date: November 13-15, 2018 (4) Reason for publication 4 Publication: THERMOPHYSICAL PROPERTIES 39 The 39th Japan Symposium 2018 Final Program Publication date: November 13, 2018 (5) Reason for publication 5 Publication Material: THERMOPHYSICAL PROPERTIES 39 The 39th Japan Symposium 2018 Publication date: November 13, 2018

The present invention relates to a thermoelectric property evaluation unit, a thermoelectric property evaluation device, and a thermoelectric property evaluation method for measuring electrical resistivity, Seebeck coefficient and thermal conductivity of thermoelectric materials.

Thermoelectric conversion materials that convert heat into electricity utilize the Seebeck effect, in which voltage is generated by creating a temperature difference between both ends of a substance. "Thermoelectric conversion," which can directly convert heat into electric power, is attracting attention as an environmentally friendly power generation technology that does not have moving parts such as turbines and does not emit carbon dioxide.

The performance of thermoelectric materials is generally defined by the figure of merit Z = α2/ρκ. where α is the Seebeck coefficient, ρ is the electrical resistivity, and κ is the thermal conductivity. The higher the value of the figure of merit Z, the better the thermoelectric material (the higher the power generation performance), but the figure of merit Z is also a function of temperature, and takes a maximum value at a certain temperature. Many experiments have been attempted to optimize materials by fine-tuning their thermoelectric performance, resistivity, and thermal conductivity.

The Seebeck coefficient α and the thermal conductivity λ are important factors that determine the thermoelectric figure of merit. That is, in the performance evaluation of thermoelectric materials, it is necessary to quantitatively determine these physical property values at a certain temperature. Generally, the thermoelectric power is determined by the stationary two-terminal method. To evaluate the performance of such a sample that is a thermoelectric material, it is necessary to position two points on the sample with high accuracy and measure the voltage and temperature at the two points.

In addition, in the case of an anisotropic sample whose properties depend on the measurement direction, the direction of the microstructure and the thermal Therefore, it was necessary to prepare the sample in consideration of the flow direction of the gas, and the load of the measurement was heavy.

As a method for measuring the electrical resistivity, Seebeck coefficient and thermal diffusivity of the same sample, for example, Patent Document 1 discloses a method in which two thermocouples are brought into contact with the side surface of a sample with a heater arranged at one end to measure the thermal diffusivity. A method of measuring the Seebeck coefficient and an electric resistivity are also disclosed.

JP 2016-24174 A

In conventional measurement methods such as those described above, the contact between a measurement probe such as a thermocouple and the sample is unstable, and a method of attaching the thermocouple to the sample with conductive paste or the like or a method of pressing the sample with the force of a spring is often used. In these methods, preparation of the sample requires time and effort, it is difficult to adjust the pressing force of the spring, and there is a problem that measurement failure occurs due to poor contact during measurement.

Therefore, the present invention can evaluate thermoelectric properties in the same measurement direction (heat flow direction) using the same measurement sample, has a simple configuration, and can perform highly accurate thermoelectric property evaluation in a short time. An object of the present invention is to provide a thermoelectric property evaluation unit, a thermoelectric property evaluation device, and a thermoelectric property evaluation method.

In order to achieve the above object, the invention according to claim 1 provides a thermoelectric property evaluation unit for evaluating the electrical resistivity, Seebeck coefficient and thermal diffusivity of a plate-shaped object to be measured made of a thermoelectric material, four measuring probes, each equipped with a thermocouple , for contacting an object and measuring the voltage and thermoelectric force from the object to be measured; holding member for supporting and holding the back surface of the object to be measured; pressing means for pressing the measurement probe against the object to be measured; and a heater for generating a temperature difference in the direction of the measurement surface of the object. A technical means is used in which the measuring portion of the measuring probe is arranged in a direction along the current or heat flow flowing through the object to be measured.

According to the invention of claim 2, in the thermoelectric property evaluation unit of claim 1, the heater is arranged so as to be able to contact the holding member at one end of the object to be measured. Use

In the invention according to claim 3, in the thermoelectric property evaluation unit according to claim 1 or 2, the pressing means includes a push rod mechanism, and a contact pressure adjustment member attached to each of the measurement probes; driving means for linearly driving the measurement probe toward the object to be measured via the contact pressure adjustment member, wherein the contact pressure adjustment member is configured such that the measurement portion of each measurement probe corresponds to the After contacting the object to be measured, a technical means is used in which the displacement by the driving means is absorbed and a pressing force is generated by the measurement unit against the object to be measured.

In the invention according to claim 4, the thermoelectric property evaluation unit according to any one of claims 1 to 3, and based on a signal that controls the thermoelectric property evaluation unit and is sent from the thermoelectric property evaluation unit and a control means for measuring the electrical resistivity, Seebeck coefficient and thermal diffusivity of the object to be measured.

The invention according to claim 5 is a thermoelectric property evaluation method using the thermoelectric property evaluation device according to claim 4, and a thermoelectric property evaluation method using the thermoelectric property evaluation device according to claim 4, a step of contacting each of the measurement probes with an object to be measured using the thermoelectric property evaluation unit; and applying a current to the object to be measured by the measurement probe, and measuring a voltage between two different points by another measurement probe. and calculating the Seebeck coefficient based on the electromotive force generated by the temperature difference between two different points measured by the measuring probe while steadily heating the object to be measured by the heater. and periodically heating the object to be measured by the heater, obtaining temperature waveform data at two different points with the measurement probe, and using the reference temperature waveform data generated by the control means to measure the difference between the two different points. calculating the phase difference of the periodic temperature changes, and calculating the thermal diffusivity based on the frequency dependence of the phase differences of the periodic temperature changes; using the technical means of

According to the first aspect of the present invention, it is possible to evaluate three thermoelectric properties in the same measurement direction (heat flow direction) using the same measurement sample with one measurement apparatus. The pressing means can reliably bring the measurement probe into contact with the evaluation sample with an appropriate pressure, so that measurement can be performed in a good contact state, and measurement accuracy and reproducibility can be improved.

By arranging the heater as in the second aspect of the invention, the heater can be brought into a contact state in which it can sufficiently supply heat to the evaluation sample, so good heating can be performed, and measurement accuracy can be improved. and reproducibility can be improved. In addition, in the thermal diffusivity measurement, by arranging the heater so as to heat the evaluation sample from the back side, the temperature wave is stabilized, so that the measurement accuracy and reproducibility can be improved.

According to the third aspect of the invention, all the measurement probes can be reliably brought into contact with the evaluation sample with an appropriate pressure by operating the driving means instead of operating each measurement probe individually. .

According to the fourth aspect of the invention, it is possible to configure a thermoelectric property evaluation device that includes a thermoelectric property evaluation unit and control means.

As in the fifth aspect of the invention, the thermoelectric property evaluation apparatus of the fourth aspect can be used to sequentially measure electrical resistivity, Seebeck coefficient and thermal diffusivity in a short time. In particular, in thermal diffusivity measurement, the time required to measure thermal diffusivity is greatly reduced. In addition, it is possible to simplify the equipment configuration required for the measurement.

1 is an overall side view of a thermoelectric property evaluation unit; FIG. In the following description, the upper side of FIG. 1 will be referred to as "upper" and the lower side as "lower". FIG. 2 is an overall plan view of the thermoelectric property evaluation unit of FIG. 1 viewed from above; It is a side view which shows the structure near a sample holder. FIG. 4 is an explanatory diagram schematically showing a state in which a measurement probe is brought into contact with a predetermined evaluation sample; It is an explanatory view showing a schematic structure of a sample holder. FIG. 4 is a plan explanatory view showing the configuration of the sample holder when viewed from the measurement probe side; It is an explanatory view for explaining composition of support means and contact pressure adjustment means. FIG. 7A is an explanatory diagram viewed from above, and FIG. 7B is an explanatory diagram viewed from a side. It is a block diagram which shows the structure of a thermoelectric property evaluation apparatus. It is explanatory drawing which shows the measurement principle of an electrical resistivity. It is an explanatory view showing the principle of measuring the Seebeck coefficient. It is explanatory drawing which shows the measurement principle of a thermal diffusivity. FIG. 4 is an explanatory diagram showing a signal processing method in thermal diffusivity measurement; It is explanatory drawing which shows the result of having changed the heating frequency and performed heat conversion factor measurement.

(Thermoelectric property evaluation unit)
A thermoelectric characterization unit of the present invention will now be described with reference to FIGS. 1-7.

The thermoelectric property evaluation unit 1 includes a measurement probe 10, a sample holder 30 that holds an evaluation sample M that is an object to be measured, a support means 40 that supports the measurement probe 10 in a predetermined arrangement, and a measurement probe 10 attached to the evaluation sample M. and a contact pressure adjusting means (hereinafter referred to as a contact pressure adjusting member 60) for adjusting the contact state of the measuring portion at the tip of the measuring probe 10 with the evaluation surface of the evaluation sample M. ing. Here, the support means 40, the drive means 50, and the contact pressure adjustment member 60 constitute a pressing means for pressing the measurement portions of the plurality of measurement probes 10 against the evaluation sample M to contact them. As the evaluation sample M, a plate-shaped sample made of a thermoelectric material can be used.

As the measurement probe 10, a first measurement probe 11, a second measurement probe 12, a third measurement probe 13 and a fourth measurement probe 14 are used. It is preferable that the measurement probe 10 be configured to be able to measure from room temperature to 1000° C. and to be usable in a vacuum atmosphere.

The first measurement probe 11 includes a thermocouple 15 and a support tube 16. The support tube 16 is internally fixed such that the measurement portion 15a at the tip of the thermocouple 15 is exposed.

The second measurement probe 12 includes a thermocouple 17 and a support tube 18. The support tube 18 is internally fixed such that the measurement portion 17a at the tip of the thermocouple 17 is exposed.

The third measurement probe 13 has the same configuration as the second measurement probe 12, and includes a thermocouple 19 and a support tube 20. The support tube 20 is arranged so that the measurement portion 19a at the tip of the thermocouple 19 is exposed. It is fixed inside.

The fourth measurement probe 14 has the same configuration as the first measurement probe 11, and includes a thermocouple 21 and a support tube 22. The support tube 22 is arranged so that the measurement portion 21a at the tip of the thermocouple 21 is exposed. It is fixed inside.

The first measurement probe 11, the second measurement probe 12, the third measurement probe 13, and the fourth measurement probe 14 are arranged in parallel at equal intervals by support means 40, which will be described later.

The support tubes 16, 18, 20, 22 are made of an insulating material with high heat resistance, and for example, an alumina tube or the like can be suitably used.

Considering the measurement at high temperatures, the thermocouples 15, 17, 19, and 21 can preferably be R thermocouples.

Measurement parts 11a, 12a, 13a, and 14a at the tips of the first measurement probe 11, the second measurement probe 12, the third measurement probe 13, and the fourth measurement probe 14 are directly brought into contact with the evaluation sample M as probes. . Therefore, a good contact state can be obtained, and the heat capacity is formed so as not to be too large. The tip of the thermocouple is usually spherical, but the measurement parts 11a, 12a, 13a, and 14a are formed so that the contact parts with the evaluation sample M are flat. As a result, the contact areas of the measuring portions 11a, 12a, 13a, and 14a with respect to the evaluation sample M can be increased, so that the measurement accuracy can be improved.

The sample holder 30 includes a holding member 31 that holds the evaluation sample M facing the measurement probe 10, and a heater 32 configured to generate a temperature gradient in the evaluation sample M.

The holding member 31 is a block-shaped member that supports and holds the back surface of the evaluation sample M, and has a holder shaft 33 extending from a flange portion 70 for attaching the thermoelectric property evaluation unit 1 to heating means such as an electric furnace. Thus, the held evaluation sample M is arranged so as to face the measuring section at each tip of the measuring probe 10 .

The holding member 31 is preferably made of a low thermal conductive material in order to reduce the influence of the temperature wave applied to the evaluation sample M in measuring the thermal diffusivity. In addition, it is preferable to efficiently prevent heat leakage through the holding member 31, which causes measurement errors, such as by increasing the porosity while maintaining the mechanical strength.

The heater 32 is a heating source capable of constant heating and periodic heating for heating the evaluation sample M from one end in order to measure thermophysical properties (Seebeck coefficient, thermal diffusivity).

The heater 32 is embedded in the holding member 31 so as to heat the evaluation sample M held by the holding member 31 from the back surface near one end. In this embodiment, it is arranged corresponding to the position pressed by the first measurement probe 11 . That is, the first measurement probe 11 is arranged at a position where it contacts the evaluation sample M on the rear side of the position where the evaluation sample M is contacted.

The support means 40 includes support members 41 that support the other ends of the measurement probes 10 and probe guides 42 that guide the measurement probes 10 .

The supporting means 40 is arranged in the plane direction of the evaluation sample M in the direction away from the heater 32 in the order of the first measuring probe 11, the second measuring probe 12, the third measuring probe 13, and the fourth measuring probe 14 at predetermined mounting intervals. Deploy.

Thereby, the measurement probe 10 is arranged in the direction along the electric current or heat flow flowing through the evaluation sample M, and each physical property can be measured in the same direction.

The support member 41a supports the end of the first measurement probe 11, the support member 41b supports the end of the second measurement probe 12, the support member 41c supports the end of the third measurement probe 13, and the support member 41c supports the end of the third measurement probe 13. 41d supports the end of the fourth measurement probe 14;

Attached to the holder shaft 33 is a probe guide 42 which guides the first measurement probe 11, the second measurement probe 12, the third measurement probe 13 and the fourth measurement probe 14 for positioning and advancing and retreating. ing. Here, the holder shaft 33 and the probe guide 42 are preferably made of quartz from the viewpoint of heat resistance.

The driving means 50 includes a driving device 51 for linear driving and a driving member 52 for linearly driving the measurement probe 10 by the driving device 51 .

The drive device 51 includes a drive portion 51a and a drive shaft 51b, and a drive member 52 is attached to the tip of the drive shaft 51b. Further, guide members 53 each having a groove for guiding one end of the support member 41 in the front-rear direction are provided.

In this embodiment, a dial gauge that converts rotation of the dial into linear drive is used as the drive device 51, but various devices can be employed as long as they are capable of linear drive.

Further, a contact pressure adjusting member 60 is attached to the driving member 52 for adjusting the contact state of the measurement portion at the tip of the measurement probe 10 with the evaluation sample M. As shown in FIG.

The contact pressure adjusting member 60 is a cylindrical member with an internal spring. When pressed from one side, the internal spring contracts to shorten the overall length and has a push rod mechanism that biases in the direction opposite to the pressing direction. .

The contact pressure adjusting member 60 is connected to each supporting member 41 so that the pressing direction is parallel to each measuring probe 10 .

The first measurement probe 11 has a contact pressure adjusting member 60a via a supporting member 41a, the second measuring probe 12 has a contact pressure adjusting member 60b via a supporting member 41b, and the third measuring probe 13 has a supporting member 41c. The contact pressure adjusting member 60c is connected to the contact pressure adjusting member 60c via the , and the contact pressure adjusting member 60d is connected to the fourth measurement probe 14 via the supporting member 41d.

A method of linearly driving the measurement probes 10 and bringing the measurement portion at the tip of each measurement probe 10 into contact with the evaluation sample M will be described.

First, the driving device 51 is operated in a state in which the measurement portion at the tip of each measurement probe 10 is separated from the evaluation sample M, and the driving member 52 is advanced toward the evaluation sample M. As shown in FIG.

When the drive member 52 advances toward the evaluation sample M, the first measurement probe 11, the second measurement probe 12, the third measurement probe 13, and the fourth measurement probe 14 simultaneously move through the contact pressure adjustment member 60 and the support member 41. Move forward with respect to the evaluation sample M.

At this time, since the first measurement probe 11, the second measurement probe 12, the third measurement probe 13, and the fourth measurement probe 14 advance while being guided by the probe guide 42, they advance while being positioned at predetermined intervals. .

When the measuring portions at the tips of the first measuring probe 11, the second measuring probe 12, the third measuring probe 13, and the fourth measuring probe 14 contact the evaluation sample M, the contact pressure adjusting member 60 operates.

Even after the measurement portion at the tip of the measurement probe 10 contacts the evaluation sample M, the support member 41 can be moved by a distance that the spring contained in the contact pressure adjustment member 60 can be displaced, and the displacement by the driving means 50 can be absorbed. can. At this time, the measurement part at the tip of the measurement probe 10 presses the evaluation sample M with an appropriate pressing force.

Since the contact pressure adjusting member 60 is provided for each of the first measurement probe 11, the second measurement probe 12, the third measurement probe 13, and the fourth measurement probe 14, the above operation is performed for each individual measurement probe 10. will be As a result, even when only the measurement portions at the tips of some of the measurement probes 10 are in contact with the evaluation sample M, all the measurement probes 10 can be moved closer to the evaluation sample M by driving the driving member 52 linearly. The measurement portion at the tip of the measurement probe 10 can be reliably brought into contact with the evaluation sample M with an appropriate pressing force. In this way, all the measurement probes 10 can be reliably brought into contact with the evaluation sample M by operating the driving means 50 instead of operating each measurement probe 10 individually.

With the above configuration, the measurement parts at the tips of the first measurement probe 11, the second measurement probe 12, the third measurement probe 13, and the fourth measurement probe 14 are accurately positioned, and the evaluation sample can be obtained without using silver paste or the like. It is possible to reliably contact M with an appropriate pressure. As a result, the thermoelectric property measurement can be performed with the measurement probe 10 in a good contact state, so that the measurement accuracy and reproducibility can be improved.

When retracting the measurement probe 10 from the evaluation sample M, the opposite operation may be performed.

(Thermoelectric property evaluation device)
As shown in FIG. 8, the thermoelectric property evaluation apparatus 2 of the present invention controls the thermoelectric property evaluation unit 1, the thermoelectric property evaluation unit 1, and based on the signal sent from the thermoelectric property evaluation unit 1, the electric resistance of the evaluation sample M. A control means 100 for measuring the modulus, the Seebeck coefficient and the thermal diffusivity, and a heating means 200 for raising the temperature of the evaluation sample M to the evaluation temperature.

The control means 100 includes a digital multimeter 110, a DC voltage/current generator 113, a function generator 114, a heater heating power source 115 for sending a control current to the heater 32, and a control device 116 such as a personal computer. ing.

The digital multimeter 110 includes a first switch card 111 that measures temperature, voltage, and resistance from between the measurement probes, and a second switch card that controls the DC current and AC signal supply circuits when measuring electrical resistivity and thermal diffusivity. 112 is built in. The digital multimeter 110 performs temperature measurement and electromotive force (voltage) measurement using the first measurement probe 11 and the fourth measurement probe 14 when measuring the Seebeck coefficient.

The first switch card 111 is connected with the first measurement probe 11 , the second measurement probe 12 , the third measurement probe 13 , the fourth measurement probe 14 , and the control device 116 .

Connected to the second switch card 112 are the first measurement probe 11 and the fourth measurement probe 14, a heater heating power source 115, a DC voltage/current generator 113, a function generator 114, and a control device 116. there is

A DC voltage/current generator 113 applies a DC current during electrical resistivity measurement and a constant heating current during Seebeck coefficient measurement.

The function generator 114 generates an AC voltage signal having an arbitrary frequency and waveform for periodically heating the heater 32 from the heater heating power supply when measuring the thermal diffusivity.

The DC voltage/current generator 113 and the function generator 114 are connected to the control device 116 .

As the heating means 200, a heating means such as an electric furnace, which is normally used for high temperature measurement, can be used.

The thermoelectric property evaluation unit 1 can also be provided with a sample chamber 210 attached to the flange portion 70 . The sample chamber 210 covers the measurement probe 10, the sample holder 30, and the like, and is formed as a chamber whose atmosphere can be controlled. For example, measurement under an inert atmosphere or a vacuum atmosphere is possible. Here, if the measurement is performed in a vacuum state, heat leakage from the evaluation sample M can be suppressed, so the measurement accuracy can be improved.

(Thermoelectric property evaluation method)
A method for measuring electrical resistivity, Seebeck coefficient and thermal diffusivity using the thermoelectric property evaluation device 2 will be described.

First, the evaluation sample M is attached to the holding member 31 of the sample holder 30 so that the heater 32 is in contact with the back surface near one end. Next, the thermoelectric property evaluation device 2 is operated to bring the measurement portion at the tip of the measurement probe 10 into contact with the evaluation sample M. As shown in FIG. After the control device 116 confirms that the measurement probe 10 is in good contact with the ohmic contact, the temperature is raised to the measurement temperature by the heating means 200, and then the measurement of the thermoelectric characteristics is started.

When the software of the controller 116 executes the measurement instruction, the electrical resistivity, the Seebeck coefficient, and the thermal diffusivity are measured once each in this order, and the measured data are stored in the controller 116 .

According to the thermophysical property evaluation method of the present invention, the thermoelectric properties necessary for obtaining the figure of merit in the development of thermoelectric materials, the electrical resistivity, the Seebeck coefficient, and the thermal diffusivity, are evaluated using an evaluation sample M of one. It can be evaluated by an evaluation device.

Moreover, since each physical property is measured by the measurement probe 10 brought into contact with the same surface of the evaluation sample M, the physical property in the same direction can be measured.

Temperature dependence of each physical property can be evaluated by setting a plurality of levels of temperature by the heating means 200 and performing measurement. Here, when the measurement temperature is raised by the heating means 200, the measurement probe 10 expands. A good contact state can be maintained without stress being applied.

A digital multimeter 110, a first switch card 111, a second switch card 112, a DC voltage/current generator 113, and a controller 116 are mainly used for measuring electrical resistivity. FIG. 9 shows the measurement principle. Circled circles 1-4 in the figure indicate contact points (measurement points) of the first measurement probe 11, the second measurement probe 12, the third measurement probe 13 and the fourth measurement probe 14, respectively. The same applies to FIGS. 10 and 11 as well.

By using the digital multimeter 110, the − side wire of the first measurement probe 11 and the − side wire of the fourth measurement probe 14 are energized to flow a current on the surface of the evaluation sample M, and the − side wire of the second measurement probe 12. and the voltage between the - side strands of the third measuring probe 13 is measured. Then, based on the obtained measurement data, the electrical resistivity ρe is calculated by the following formula. Here, the correction coefficient f ₁ is a value that depends on the sample thickness t [m] and the heater-sensor distances d ₁ and d ₂ [m], and the correction coefficient f ₂ is the heater-sensor distance d ₁ , It is a value that depends on d ₂ [m] and the length l [m] of the sample in the transverse direction.

Digital multimeter 110, first switch card 111, second switch card 112, DC voltage/current generator 113, heater heating power source 115, and controller 116 are mainly used for measuring the Seebeck coefficient. FIG. 10 shows the measurement principle.

A DC voltage/current generator 113 applies a DC voltage to the heater 32 via a heater heating power supply 115 to steadily heat the evaluation sample M. FIG. The electromotive force generated by the temperature difference between the contact portions is measured by the first measurement probe 11 and the fourth measurement probe 14 . Then, the Seebeck coefficient is calculated by the following formula based on the obtained measurement data.

A digital multimeter 110, a first switch card 111, a second switch card 112, a function generator 114, a heater heating power supply 115, and a controller 116 are mainly used for measuring the thermal diffusivity. The measurement principle is shown in FIGS. 11 and 12. FIG.

First, the evaluation sample M is cyclically heated by periodically applying a voltage to the heater 32 via the heater heating power supply 115 by the function generator 114 . The respective temperatures (temperature 2 and temperature 3) are measured by the second measurement probe 12 and the third measurement probe 13, and temperature waveform data is taken into the controller 116. FIG. Then, from the waveforms of temperature 2 and temperature 3, the temperature response difference (phase difference) between the second measurement probe 12 and the third measurement probe 13 and the frequency dependence of this phase difference are used to lower the thermal diffusivity a. Calculated by the formula.

When the evaluation sample M is pressed by the first measurement probe 11 , the heater 32 is pressed from the rear surface of the evaluation sample M with a constant contact pressure. As a result, the heater 32 can sufficiently supply heat to the evaluation sample M, so that good heating can be achieved, and measurement accuracy and reproducibility can be improved. Further, by arranging the heater 32 so as to heat the evaluation sample M from the rear surface, the temperature wave is stabilized, so that the measurement accuracy and reproducibility can be improved.

In the measurement of the thermal diffusivity, the use of the inner two second measurement probes 12 and the third measurement probe 13 makes it easy to obtain the amplitude of the temperature wave from the heater 32, and the heat conduction of the evaluation sample M in the thickness direction of the sample. is negligible and can be treated as heat conduction only in the surface direction (heat flow direction).

In the conventional periodic heating method, when the sample is heated by laser heating,
・Problems due to differences in light absorption of the sample ・It is difficult to focus the light ・The equipment configuration is complicated There were some problems.

In addition, in the method of heating the test sample by contacting the heater block with one end, it is difficult to generate a temperature change at a high frequency due to the large heat capacity of the heater. However, the range of measurable thermal diffusivities of materials is severely limited.

The heater 32 is small and has a small heat capacity, and the heat generated by the heater 32 is surrounded by the holding member 31 having a small thermal conductivity. be. This makes it possible to generate temperature changes in the sample at high frequencies. Moreover, since the time difference can be reduced even in the case of low frequencies, the measurement accuracy can be improved.

The method for measuring the thermal diffusivity of the present invention will be described in detail below.

The heater 32 starts cyclic heating of the evaluation sample M, and the temperature waveform data of the second measurement probe 12 near the heater 32 and the temperature waveform data of the third measurement probe 13 far from the heater 32 are measured by the digital multimeter 110. Then, the controller 116 takes in two waveform data.

The measurement signal is multiplied by a signal in phase with the measurement signal and a signal phase-shifted by 90° from the measurement signal, respectively, to detect the frequency component equal to that of the measurement signal. A reference signal (reference temperature waveform data generated by the controller 116) is obtained from the in-phase component X of the measurement signal and the quadrature component Y of the measurement signal, which are obtained by passing each of the obtained detection signals through a low-pass filter. The phase difference .theta. of the measured signal with respect to is obtained from .theta.=arctan(Y/X).

Regarding the above phase difference θ, if the phase difference obtained by the second measuring probe 12 closer to the heater 32 is θ1, and the phase difference obtained by the third measuring probe 13 farther from the heater 32 is θ2, the phase difference between the two points is It is obtained by θ2-θ1.

Repeat the above procedure for measurement in the specified frequency range, and end the measurement. Then, from the values recorded in the control device 116, the phase difference between the second measuring probe 12 and the third measuring probe 13 for each frequency is calculated, and the least squares method is obtained from the plot of the phase difference against (frequency) ^1/2 . The thermal diffusivity is obtained from the slope of the first-order approximation formula derived using

In the conventional thermal diffusivity measurement, the following method is used.

The evaluation sample is cyclically heated with a heater, and the phase difference and amplitude between the thermophysical property measurement probe near the heater and the modulation voltage of the function generator supplied to the heater are measured with a lock-in amplifier. When the phase difference stability condition is satisfied, the value of the phase difference is recorded. Next, the value input to the lock-in amplifier is switched from the thermophysical property measuring probe closer to the heater to the thermophysical property measuring probe farther from the heater, the same measurement is performed, and the value of the phase difference is recorded. Then, from the recorded values, the phase difference between the two points of the thermophysical property measurement probe is calculated for each frequency, and the first-order approximation formula derived using the least squares method from the plot of the phase difference against (frequency) ^1/2 The thermal diffusivity is obtained from the slope of (For example, I. Hatta, K. Fujii, A. Sakakibara, F. Takahashi, Y. Hamada and Y. Kaneda: Jpn. J. Appl. Phys., 38 (1999) 2988.)

Since the signal strength of thermoelectric materials is small, the conventional thermal diffusivity measurement has the disadvantage that lock-in takes a long time and the measurement time is long.

According to the thermal diffusivity measurement of the present invention, the temperature waveform data of the second measurement probe 12 and the temperature waveform data of the third measurement probe 13 are generated inside the control device 116 after the two waveform data are taken into the control device 116. Since arithmetic processing is performed using the obtained signal waveform, measurement is possible even if the signal strength from the evaluation sample M is small, and there is no need to wait until lock-in occurs as in conventional measurement methods, and a lock-in amplifier is used. The time required to measure the thermal diffusivity is greatly shortened. In addition, it is possible to simplify the equipment configuration required for the measurement.

The heater 32 can also be installed via a planar member on which the evaluation sample M can be placed on the surface of the holding member 31 .

The heater 32 can also be configured so as to be able to contact one end of the evaluation sample M from the measurement surface side, for example, as a structure in which a push rod type heater is pressed from the measurement surface side.

Instead of the heater 32, it is also possible to employ a cooling unit that cools one end of the evaluation sample M to generate a temperature difference.

(Effect of Embodiment)
According to the thermoelectric property evaluation unit 1, the thermoelectric property evaluation device 2, and the thermoelectric property evaluation method of the present invention, one measurement device uses the same evaluation sample M, and the electrical resistivity and Seebeck coefficient are measured in the same measurement direction (heat flow direction). and thermal diffusivity can be measured. The contact pressure adjusting member 60 can reliably bring the measurement probe 10 into contact with the evaluation sample M with an appropriate pressure, thereby improving measurement accuracy and reproducibility.

Using the thermoelectric property evaluation device 2, electrical resistivity, Seebeck coefficient and thermal diffusivity can be sequentially measured in a short period of time. In particular, in thermal diffusivity measurement, the measurement time can be significantly shortened as compared with the case where a lock-in amplifier is used, and the device configuration required for measurement can be simplified.

The measurable frequency of thermal diffusivity was investigated. Thermal diffusivity was measured at room temperature in the atmosphere for a thin plate-like thermoelectric conversion element (bismuth tellurium Bi ₂ Te ₃ ). Based on (Formula 3), the heating frequency f is in the range of 0.01 to 1.0 [Hz], the distance between sensors d ₂ - _{d 1} is 3 [mm], and the phase delay difference φ ₂ - φ ₁ [deg] was measured. Also, the power of the heater was set to about 0.37 [W]. FIG. 13 shows an example of thermal diffusivity measurement results. The horizontal axis represents the square root f ^1/2 [Hz ^1/2 ] of the heating frequency, and the vertical axis represents the phase delay difference φ ₂ -φ ₁ [deg]. From this result, the slope of the first-order approximate straight line calculated by the method of least squares corresponds to the denominator ((φ ₂ −φ ₁ )/f ^1/2 )) of (Formula 3), so the thermal diffusivity can be obtained. can.

Since a thermoelectric conversion element generally has a low thermal conductivity, the amplitude of the temperature wave detected by the thermocouple tends to decrease as the heating frequency f increases, making it impossible to accurately detect the phase delay difference φ ₂ -φ ₁ . From FIG. 13, in the present embodiment, in the region where the heating frequency f is about 0.025 to 0.22 Hz, the square root of the heating frequency f ^1/2 [Hz ^1/2 ] and the phase delay difference φ ₂ −φ ₁ [deg ], the thermal diffusivity was calculated within this range. As a result, the thermal diffusivity a was estimated to be 1.83 mm ² /s, and it was confirmed that a general thermoelectric material can be measured. Moreover, since the measurable frequency changes depending on the thermal conductivity of the material to be measured, the power of the heater, etc., it is necessary to appropriately set appropriate conditions.

REFERENCE SIGNS LIST 1 thermoelectric property evaluation unit 2 thermoelectric property evaluation device 3 control means 10 measurement probe 11 first measurement probe 12 second measurement probe 13 third measurement probe 14 fourth measurement probe 15 first thermocouple 15a... Measuring part 16... First supporting tube 17... Second thermocouple 17a... Measuring part 18... Second supporting tube 19... Third thermocouple 19a... Measuring part 20... Third supporting tube 21... Fourth thermocouple 21a... Measurement part 22 Fourth support tube 30 Sample holder 31 Holding member 32 Heater 33 Holder shaft 40 Supporting means 41 Supporting members 41a, 41b, 41c, 41d Supporting member 42 Probe guide 50 Driving means 51 Driving device 51a Driving unit 51b Driving shaft 52 Driving member 53 Guide member 60 Contact pressure adjusting members 60a, 60b, 60c, 60d Contact pressure adjusting member 70 Flange 100 Control means 110 Digital multimeter Reference Signs List 111 First switch card 112 Second switch card 113 DC voltage/current generator 114 Function generator 115 Heater heating power source 116 Control device 200 Heating means 210 Sample chamber M Evaluation sample

Claims (5)

A thermoelectric property evaluation unit that evaluates the electrical resistivity, Seebeck coefficient and thermal diffusivity of a plate-shaped object to be measured made of a thermoelectric material,
four measurement probes, each equipped with a thermocouple, for contacting the object and measuring the voltage and thermoelectric force from the object;
a holding member that supports and holds the back surface of the object to be measured, which is opposite to the measurement surface on which the object to be measured contacts the measurement probe;
pressing means for pressing each of the measurement probes against an object to be measured;
a heater for steadily heating or cyclically heating one end of the object to be measured to generate a temperature difference in the direction of the measurement surface of the object;
with
Each of the measurement probes is configured such that a thermocouple is passed through a support tube made of an insulator and a tip thereof protrudes as a measurement portion. A thermoelectric property evaluation unit, characterized in that it is arranged in 2. The thermoelectric property evaluation unit according to claim 1, wherein the heater is arranged so as to be in contact with the holding member at one end of the object to be measured. The pressing means is
a contact pressure adjusting member having a push rod mechanism and attached to each of the measurement probes;
driving means for linearly driving the measurement probe toward the object to be measured via the contact pressure adjusting member;
In each measurement probe, the contact pressure adjusting member absorbs the displacement caused by the driving means after the measurement unit contacts the object to be measured, and causes the measurement unit to generate a pressing force against the object to be measured. The thermoelectric property evaluation unit according to claim 1 or 2, characterized by: A thermoelectric property evaluation unit according to any one of claims 1 to 3;
a control means for controlling the thermoelectric property evaluation unit and measuring the electrical resistivity, Seebeck coefficient and thermal diffusivity of the object to be measured based on signals sent from the thermoelectric property evaluation unit;
A thermoelectric property evaluation device comprising: A thermoelectric property evaluation method using the thermoelectric property evaluation device according to claim 4,
a step of contacting each of the measurement probes with an object to be measured using the thermoelectric property evaluation unit;
A step of applying a current to the object to be measured by the measurement probe and calculating an electrical resistivity based on a voltage between two different points measured by another measurement probe;
a step of steadily heating the object to be measured by the heater and calculating a Seebeck coefficient based on an electromotive force generated by a temperature difference between two different points measured by the measurement probe;
The object to be measured is cyclically heated by the heater, the temperature waveform data of two different points are obtained by the measurement probe, and the reference temperature waveform data generated by the control means is used to cyclically heat the object to be measured between the two different points. calculating a phase difference of temperature changes, and calculating a thermal diffusivity based on the frequency dependence of the phase differences of periodic temperature changes based on the frequency dependence of the phase differences of periodic temperature changes; A method for evaluating thermoelectric properties, comprising:

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