LSR-3
Seebeck-Coefficient / Resistivity / Harman-Method / ZT of Modules
Description
On point
The Linseis LSR-Platform provides comprehensive characterization of thermoelectric materials, encompassing both solid materials and thin films. In its basic version, the LSR-3, it allows for fully automated and simultaneous measurements of both the Seebeck Coefficient and Electrical Conductivity (or resistivity) of solid materials, with a maximum temperature capability of 1500°C.
The basic version can be enhanced with various options to broaden its range of applications. For instance, the low-temperature option facilitates fully automated measurements with LN2 cooling, reaching temperatures as low as -100°C. By using a specialized thin-film adapter, the measurement range can be extended to include foils and thin layers. An optional camera enables the precise determination of electrical conductivity, and the “high-ohm” option significantly expands the measuring range, accommodating samples with low electrical conductivity.
To calculate the thermoelectric figure of merit, ZT, which is a crucial parameter for assessing the efficiency of thermoelectric materials, knowledge of the material’s thermal conductivity is required, in addition to the Seebeck Coefficient and electrical conductivity. Typically, a separate measuring device, like a LaserFlash, is needed for thermal transport parameter measurements.
To address this challenge, there are two options: either integrating an additional LaserFlash into the Linseis LSR platform (referred to as LZT-Meter) or using a special adapter that enables the characterization of solid materials using the Harman method. The Harman method allows for direct ZT determination, which, when combined with the two original measurements of the Seebeck Coefficient and electrical conductivity, provides insights into the thermal conductivity of the material. An LSR platform equipped with the Harman method is denoted as the LSR-4, offering significant added value.
Through an optional extension of the measuring electronics, the LSR-4 Platform can also determine ZT values for modules (Thermoelectric Generators, TEG) using impedance spectroscopy, following the same fundamental measuring principles.
Principle of Seebeck-Coefficient measurement
A sample, which can be cylindrical, square-shaped, or rectangular, is positioned vertically between two electrodes. The lower electrode block, and optionally the upper electrode block (used for inverting the temperature gradient), contains a heating coil (secondary heater). The entire measurement setup is enclosed in a furnace, which raises the sample’s temperature to the desired level for the measurement.
Once the target temperature is achieved, the secondary heater in the lower electrode generates a predetermined temperature gradient along the sample. Two thermocouples, T1 and T2, make lateral contact with the sample and measure the temperature difference (ΔT = T2 – T1) between the hot and cold contact points on the sample. Additionally, one of the two thermocouple leads is utilized to measure the electromotive force, dE, or thermovoltage, Vth, that is generated during the process.
A unique spring mechanism is employed to ensure optimal electrical contact between the thermocouples and the sample, ensuring highly accurate measurements. With the collected measurement data, the Seebeck Coefficient can be easily calculated using the following formula:
Principle of the resistivity measurement
To determine the specific electric resistance or electrical conductivity of the sample, the DC four-terminal measurement technique is employed. This method effectively suppresses parasitic influences such as contact or wire resistances, leading to a significant enhancement in measurement accuracy.
For measurements under thermal equilibrium conditions (ΔT = 0K), a constant direct current (IDC) is applied to the sample through the two electrodes. Given the dimensions of the electrodes and the sample, it is reasonable to assume nearly ideal one-dimensional current flow within the sample. The resulting voltage drop (VΩ) across a segment of length “t” within the sample is measured using one of the two thermocouple wires.
Using the collected data and the thermocouple distance “t,” the specific resistance and electrical conductivity can be calculated based on the following formulas:
Principle of a Harman measurement
The Harman method is a technique used to calculate the thermoelectric figure of merit, ZT, of a material by analyzing the temporal voltage curve generated when a direct current (DC) is applied to a sample.
In this method, a current is introduced into a thermoelectric sample through two needle contacts. As a result of the Peltier effect, one of the two transitions experiences local heating or cooling. This leads to the establishment of a distinctive temperature profile across the sample, governed by adiabatic boundary conditions. By calculating the ratio of the initial voltage drop (representing the ohmic part without a temperature gradient) to the steady-state voltage drop (which includes the thermal voltage), the dimensionless figure of merit ZT, and consequently the thermal conductivity lambda, can be determined.
The fundamental advantages of the Harman method, in comparison to calculating ZT from individual measurements, are that it necessitates the use of a single instrument, requires the preparation of only one sample, and results in a significantly smaller measurement error for ZT due to direct measurement. However, it’s worth noting that this method is applicable primarily to high-quality thermoelectric materials and is limited to temperatures of up to 400°C.
Adapter for thin films and foils
In recent years, the interest in nanostructured samples, like thin films or nanowires, has grown considerably due to their distinct properties compared to bulk materials. To address the needs of contemporary research, LINSEIS has introduced two distinct sample holders designed for free-standing films, as well as films or coatings applied to a substrate, compatible with the LSR platform. These innovative sample holders are uniquely designed to enable the characterization of a diverse array of samples, varying in coating thickness and production methods, using the LSR system.
Available accessories
Sample holder for disk shaped samples
The LSR-Platform accommodates measurements with different sample geometries, including cylindrical samples (up to ø 6 mm x 23 mm in height), rod-shaped samples (with a footprint of up to 5 mm x 5 mm and 23 mm in height), or disc-shaped samples (10 mm, 12.7 mm, or 25.4 mm in diameter). Ideally, the sample’s footprint area should be equal to or smaller than the surface area of the electrodes to ensure a one-dimensional flow of heat and electricity through the sample.
In the basic configuration, two distinct sample holders are available for measurements. While cylindrical and rod-shaped samples are the typical choice for thermoelectric generators (TEG), thermal conductivity measurements using Laser or Light-Flash systems often require disc-shaped sample geometries. To streamline the measurement process, reduce the need for extensive sample preparation, and minimize potential sources of error from the outset, an optional sample holder (developed in collaboration with the German Aerospace Center, DLR) can be integrated into the LSR platform. This holder facilitates the measurement of the Seebeck Coefficient and Electrical Conductivity for disc-shaped samples.
Thermoelements and Camera-Option
Standard thermocouple: Ideal for the utmost precision.
Sheathed thermocouple: Suited for demanding samples.
Type K/S/C thermocouples:
– Type K for low-temperature measurements
– Type S for high-temperature measurements
– Type C for samples prone to Pt poisoning.
Camera Option: Enables precise probe distance measurements and enhances accuracy in resistivity measurements.
Software Package Included.
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Specifications
All facts on your hand
Key Features:
– Almost ideal one-dimensional (1-D) heat flux through the sample.
– The high-ohm option, along with adjustable thermocouple positioning, ensures reliable measurements even for the most challenging samples.
– Interchangeable furnaces support measurements spanning from -100°C to 1500°C.
– Direct ZT measurement for both individual legs (using the Harman method) and modules (via impedance spectroscopy).
– Thermal conductivity measurement utilizing the Harman method.
– High-speed infrared furnace for exceptional temperature control during measurements, increasing sample throughput.
– A wide variety of thermocouples are available for diverse measurement needs.
– The camera option enhances precision in resistivity measurements.
| Model | LSR-3 |
|---|---|
| Temperature range: | Infrared furnace: RT to 800°C/1100°C Resistance furnace: RT to 1500°C Low temperature furnace: -100°C to 500°C |
| Principles of measurement: | Seebeck-Coefficient: Steady state DC-method / Slope-method Resistivity: DC Four Terminal measurement |
| Atmospheres: | Inert, reducing, oxidizing, vacuum Low pressure helium gas recommended |
| Sample holder: | Vertical between two electrodes Optional adapter for thin films and foils |
| Sample size (Cylindric or Rectangular): | 2 to 5 mm footprint and max. 23 mm long up to 6 mm in diameter and max. 23 mm long |
| Sample size (Disc-shaped): | 10, 12.7, 25.4 mm |
| Adjustable probe distance: | 4, 6, 8 mm |
| Watercooling: | required |
| Measurement range Seebeck-Coefficient: | 1µV/K to 250mV/K (static dc method) Accuracy ±7% / Reproducibility ±3,5% |
| Current source: | Excellent long term stability from 0 up to 160 mA |
| Electrode material: | Nickel (-100 up to 500°C) / Platinum (-100 up to +1500°C) |
| Thermocouples: | Type K/S/C |
| ADDON | LSR-4 UPGRADE |
|---|---|
| DC Harman-Method: | Direct ZT-Determination on thermoelectric legsC |
| AC Impedance-Spectroscopy: | Direct ZT-Determination on thermoelectric modules (TEG/Peltier-Module) |
| Temperature range: | -100 up to +400°C RT up to +400°C |
| Sample holder: | Needle contacts for adiabatic measurement conditions |
| Sample size: | 2 to 5 mm (rectangular)and max. 23 mm long up to 6 mm in diameter and max. 23 mm long Modules up to 50mm x 50mm |
Software
Make values visible and comparable
The LINSEIS thermal analysis software is a powerful, Microsoft® Windows®-based solution that plays a pivotal role in the preparation, execution, and evaluation of thermoanalytical experiments, complementing the hardware used. This software package, developed by our in-house software specialists and application experts, has a proven track record over the years.
Key Features:
– Automatic evaluation of the Seebeck Coefficient and Electrical Conductivity
– Automatic control of sample contacting
– Creation of automatic measurement programs
– Establishment of temperature profiles and gradients for Seebeck measurements
– Optional automatic evaluation of Harman measurements
– Real-time color rendering
– Options for automatic and manual scaling
– Freedom to choose axes representation (e.g., temperature on the x-axis and delta L on the y-axis)
– Mathematical calculations, including first and second derivatives
– Database for archiving all measurements and evaluations
– Multitasking support (multiple programs can run simultaneously)
– Multi-user option with user accounts
– Zoom options for curve analysis
– Capability to overlay and compare any number of curves
– Online Help Menu
– Custom labeling of curves
– Streamlined export functions, including CTRL C
– EXCEL® and ASCII export of measurement data
– Ability to calculate zero curves
– Statistical trend evaluation, including mean value curve with a confidence interval
– Tabular data presentation
Applications
Application example: Constantan (High-temperature reference)
Unlike the NIST Bi2Te3 reference sample (SRM 3451)™, which is limited to a temperature range up to 390 K, our alternative constantan reference sample serves as a high-temperature reference up to 800°C. The presented measurement illustrates a typical acceptance curve well within the specified tolerances.
Application example: ZT-Determinaton of the NIST Bi2Te3 reference sample using the Harman-Method
This measurement involves the NIST (SRM 3451)™ Bi2Te3 reference sample and employs the Harman method for direct ZT measurement with the LINSEIS LSR-Platform. The figure shows the characteristic voltage distribution of the measurement, and the evaluation is based on the resistive component of the voltage in relation to the thermoelectric voltage. The presented measurement is a single data point at room temperature.
Application example: SiGe-alloy
Silicon germanium alloys are thermoelectric materials with high-temperature stability, often used in demanding environmental conditions, such as space missions or for waste heat recovery at elevated temperatures. The measurement presented here aims to assess the low-temperature behavior of a newly developed alloy.
External Applications:
– Thermoelectric properties of Al-substituted tetrahedrite (published in the Journal of Applied Physics)
– Study on the magnetocaloric and thermoelectric application potential of the ferromagnetic compound CeCrGe3 (published in the Journal of Applied Physics)
– Microstructure and mechanical properties of pure copper wire produced by shear-assisted processing and extrusion (published in The Journal of The Minerals, Metals & Materials Society)
– Magnon drag effect in Fe-Co alloys (published in the Journal of Applied Physics)
Are you intrigued by the LSR?
Do you require further details?
Feel free to get in touch with our knowledgeable application experts!
Downloads
Everything at a glance
LSR Product Brochure (PDF)
