An apparatus for simultaneous measurement of electrical conductivity and thermopower of thin films in the temperature range of 300-750 K

Contributed Review: Instruments for measuring Seebeck coefficient of thin film thermoelectric materials: A mini-review

Thin film thermoelectric materials (TF TEMs) based on organic semiconductors or organic/inorganic composites exhibit unique properties such as low-temperature processability, mechanical flexibility, great freedom of material design, etc. Thus they have attracted a growing research interest. Similar to inorganic bulk thermoelectric materials (IB TEMs), the Seebeck coefficient combined with electrical conductivity and thermal conductivity is a fundamental property to influence the performance of TF TEMs. However, due to the differences in material and sample geometries, the well-established characterization devices for IB TEMs are no longer applicable to TF TEMs. And until now, a universal standard of measuring the Seebeck coefficient of TF TEMs is still lacking. This mini-review presents the development of instruments designed for measuring the Seebeck coefficient of TF TEMs in the last decade. Primary measurement methods and typical apparatus designs will be reviewed, followed by an error analysis induced by instrumentation. Hopefully this mini-review will facilitate better designs for a more accurate characterization of the Seebeck coefficient of thin film thermoelectric materials.

A Simple and Portable Setup for Thermopower Measurements

Thermoelectric energy conversion technology has received significant attention because of its promising applications and environmentally clean nature. The innovative design of efficient thermoelectric materials is assisted by simple and reliable techniques for fast and accurate testing. Here, a simple approach for rapid measurement of the Seebeck coefficient is described using commonly available materials based on hot and cold probes; both probes are heated by built-in microheaters. A spring-loaded sample mounting arrangement provides easy sample loading/unloading. The setup is suitable for measurements on a wide range of materials, such as pellets, films, and even soft surfaces without damage. Several known thermoelectric materials, such as alumel, bismuth, and silicon, yielded values close to reported ones. The setup is very compact, simple, fast, low cost, and reliable to develop as a laboratory characterization tool.

Measurement of the thermoelectric power factor of films over the 10-400 K range

The design and development of a novel apparatus for the simultaneous measurement of electrical resistivity and Seebeck coefficient of films is reported here. Mounting stage is integrated inside a cryostat chamber enabling measurements over the 10-400 K temperature range, intended for organic thermoelectrics. Finite element method was used to analyze the thermo-mechanical response of the sample holder. The apparatus was validated against high purity nickel film, and a very good agreement was found.

High temperature setup for measurements of Seebeck coefficient and electrical resistivity of thin films using inductive heating

We have developed an automated setup for simultaneous measurement of Seebeck coefficient S(T) and electrical resistivity ρ(T) of thin film samples from room temperature to ∼650 °C. S and ρ are extracted from current-voltage (I-V) measurements obtained using a semiconductor parameter analyzer and temperature measurements obtained using commercial thermocouples. The slope and the x-axis intercept of the I-V characteristics represent the sample conductance G and the Seebeck voltage, respectively. The measured G(T) can be scaled to ρ(T) by the geometry factor obtained from the room temperature resistivity measurement of the film. The setup uses resistive or inductive heating to control the temperature and temperature gradient on the sample. Inductive heating is achieved with steel plates that surround the test area and a water cooled copper pipe coil underneath that generates an AC magnetic field. The measurements can be performed using resistive heating only or inductive heating only, or a combination of both depending on the desired heating ranges. Inductive heating provides a more uniform heating of the test area, does not require contacts to the sample holder, can be used up to the Curie temperature of the particular magnetic material, and the temperature gradients can be adjusted by the relative positions of the coil and sample. Example results obtained for low doped single-crystal silicon with inductive heating only and with resistive heating only are presented.

New experimental methodology, setup and LabView program for accurate absolute thermoelectric power and electrical resistivity measurements between 25 and 1600 K: application to pure copper, platinum, tungsten, and nickel at very high temperatures

In this paper we describe an experimental setup designed to measure simultaneously and very accurately the resistivity and the absolute thermoelectric power, also called absolute thermopower or absolute Seebeck coefficient, of solid and liquid conductors/semiconductors over a wide range of temperatures (room temperature to 1600 K in present work). A careful analysis of the existing experimental data allowed us to extend the absolute thermoelectric power scale of platinum to the range 0-1800 K with two new polynomial expressions. The experimental device is controlled by a LabView program. A detailed description of the accurate dynamic measurement methodology is given in this paper. We measure the absolute thermoelectric power and the electrical resistivity and deduce with a good accuracy the thermal conductivity using the relations between the three electronic transport coefficients, going beyond the classical Wiedemann-Franz law. We use this experimental setup and methodology to give new very accurate results for pure copper, platinum, and nickel especially at very high temperatures. But resistivity and absolute thermopower measurement can be more than an objective in itself. Resistivity characterizes the bulk of a material while absolute thermoelectric power characterizes the material at the point where the electrical contact is established with a couple of metallic elements (forming a thermocouple). In a forthcoming paper we will show that the measurement of resistivity and absolute thermoelectric power characterizes advantageously the (change of) phase, probably as well as DSC (if not better), since the change of phases can be easily followed during several hours/days at constant temperature.

An experimental setup for the simultaneous measurement of thermoelectric power of two samples from 77 K to 500 K

We report on an experimental setup for the simultaneous measurement of the thermoelectric power (TEP) of two samples in the temperature range from 77 K to 500 K using optimum electronic instruments. The setup consists of two rectangular copper bars in a bridge arrangement for sample mounting, two surface mount (SM) chip resistors for creating alternate temperature gradient, and a type E thermocouple in differential geometry for gradient temperature (ΔT) measurement across the samples. In addition, a diode arrangement has been made for the alternate heating of SM resistors using only one DC current source. The measurement accuracy of ΔT increases with the differential thermocouple arrangement. For the calibration of the setup, measurements of TEP on a high purity (99.99%) platinum wire and type K thermocouple wires Chromel and Alumel have been performed from 77 K to 500 K with respect to copper lead wires. Additionally, this setup can be utilized to calibrate an unknown sample against a sample of known absolute TEP.

Multifunctional probes for high-throughput measurement of Seebeck coefficient and electrical conductivity at room temperature

An apparatus capable of rapid measurement of the Seebeck coefficient and electrical resistivity at room temperature is reported. The novel aspect of this apparatus is the use of 4 multifunctional probes that comprise a junction of two conductors at the tip and serve as both thermocouples and electrical contacts. In addition, one of the probes has a built-in heater that can establish a temperature gradient in the sample for the Seebeck measurement. The technique does not require special sample geometries or preparation of contacts and is suitable for bulk and thin film materials. Together with automated sample stage and data acquisition, the equipment is able to measure both the Seebeck coefficient and electrical resistivity in less than 20 s with good accuracy. Less than 5% and 4% relative errors were found for the measurement of the Seebeck coefficient and electrical resistivity, respectively. This makes the apparatus especially useful for high throughput evaluation of thermoelectric materials.

An experimental apparatus for simultaneously measuring Seebeck coefficient and electrical resistivity from 100 K to 600 K

In this paper, we report a fully automated experimental apparatus for measuring Seebeck coefficient and electrical resistivity of a sample simultaneously in a temperature range of 100-600 K. The Seebeck coefficient is measured using a quasi-steady temperature differential method in which two ceramic heaters are employed to alternately heat the sample. The sample holder is designed to reduce temperature disturbance on its base during a measurement cycle. To demonstrate the accuracy and reliability of the experimental setup, we have performed tests on reference materials including constantan and platinum.

Fully automated measurement setup for non-destructive characterization of thermoelectric materials near room temperature

A measurement setup is presented that allows for a complete and non-destructive material characterization of electrochemically deposited thermoelectric material. All electrical (Seebeck coefficient α, electrical conductivity σ), thermal (thermal conductivity λ), and thermoelectric (figure of merit ZT) material parameters are determined within a single measurement run. The setup is capable of characterizing individual electrochemically deposited Bi(2+x)Te(3-x) pillars of various size and thickness down to a few 10 μm, embedded in a polymer matrix with a maximum measurement area of 1 × 1 cm(2). The temperature range is limited to an application specific window near room temperature of 10 °C to 70 °C. A maximum thermal flux of 1 W/cm(2) can be applied to the device under test (DUT) by the Peltier element driven heat source and sink. The setup has a highly symmetric design and DUTs can be mounted and dismounted within few seconds. A novel in situ recalibration method for a simple, quick and more accurate calibration of all sensors has been developed. Thermal losses within the setup are analysed and are mathematically considered for each measurement. All random and systematic errors are encountered for by a MATLAB routine, calculating all the target parameters and their uncertainties. The setup provides a measurement accuracy of ±2.34 μV/K for α, ±810.16 S/m for σ, ±0.13 W/mK for λ, and ±0.0075 for ZT at a mean temperature of 42.5 °C for the specifically designed test samples with a pillar diameter of 696 μm and thickness of 134 μm, embedded in a polyethylene terephthalate polymer matrix.