Seebeck-Coefficient & Resistivity
Using the Linseis LSR-Platform, thermoelectric materials in the form of bulk materials and thin films can be characterized in an easy and comfortable manner. In the basic version – LSR-1, both the Seebeck-Coefficient and the Electric Resistance can be measured fully automatically and simultaneously from -160°C up to 200°C.
The basic version of the LSR-1 (RT up to 200°C) can be combined with various options to expand the range of applications. For example, the low-temperature option allows fully automatic measurements with LN2-cooling down to -160°C as well as quench cooling to 80 K (resistivity only). An optional high temperature probe stage allows resistivity measurements up to 600°C. With the illumination option it is possible to perform thermoelectric measurements under a defined influence of light, using a 3-Wavelength LED light source on the LSR-1.
The LSR-1 System permits the characterization of metallic and semiconducting samples according to the well-known Van-der-Pauw (Resistivity) as well as static DC and slope Seebeck-Coefficient measurement technique.
The compact desktop setup allows a fully automatic and software controlled operation. The comprehensive Windows based software provides an easy to use user interface, including wizards for setting up a measurement profile, feedbacks for the reliability of the measurement data and an integrated measurement data evaluation and storage the vacuum tight measurement chamber in combination with a selection of gas dosing systems ensures that all fields of application can be covered.
Principle of Seebeck-Coefficient measurement
- The sample temperature as well as temperature gradient are controlled by a heater embedded inside the sample holder.
- The environmental temperature can be cooled down to about -160°C. That makes Seebeck coefficient measurement possible up to 180°C mean sample temperature. Resistivity can be measure down to -160°C.
- Enhanced precision temperature measurement: The single TC wires touch the sample suface orthogonally to the direction of temperature gradient. Both contact spots share the same temperature. Using this method the sample surface temperature is measured instead of the temperature of a TC bead pressed to the sample surface. This way it is also irrelevant if the temperature of the sample surface is affected by the TC wires transferring heat from/towards the sample.
- Enhanced precision thermovoltage measurement: The Seebeck voltage is measured between both negative TC wires, which allows the most accurate spatial allocation between temperature and thermovoltage measurement. So the Seebeck voltage occurs in the exact same spots where temperature is measured.
- Seebeck voltage is recorded along with the temperature gradient whilst the gradient heater power is linearly increased. The duration of a single measurement-sweep is about 30 to 90s incl. high speed sampling rate. Values are samples once a second.
- The slope of the Thermovoltage over Delta T is fitted with a linear polynomial regression. Thanks to this dynamic evaluation method, occuring offsets in temperature gradient measurement can be neglegted and the measurement accuracy is increased. Due to the short duration of the actual measurement, offset drifts have very low impact on the result.
Principle of the resistivity measurement
In order to determine the specific electric resistance (or the electrical conductivity) of the sample, the Van der Pauw measurement technique is used. As a result, samples of arbitrary shape can be analyzed and parasitic influences such as contact or wire resistances are suppressed and the measurement accuracy can be significantly increased.
For the Van der Pauw measurement, the sample needs to be connected with four electrodes directly on the edge. In the first step of the routing, a current is caused to flow along two contacts at one edge of the sample and the voltage across the other two contacts on the opposite edge is measured. From these two values, a resistance can be found using Ohm’s law. In the second step, the contacts are cyclically switched and the measurement will be repeated. The sheet resistance of the sample can then easily be calculated by inserting the two measured resistances (horizontal and vertical) into the Van der Pauw formula and solving it.
Based on the measured data and the thermocouple distance “t”, the specific resistance and the electrical conductivity can be calculated according to the following formulas:
All facts on your hand
- Modular system design. Can be upgraded with gas dosing system, illumination and Cryo-option.
- Vacuum tight measurement chamber for measurements under defined atmospheres.
- Easy to use and exchangeable sample holders, with integrated primary and secondary heater.
- Integrated state of the art measurement electronics provides most accurate results for challenging samples.
- The unit can be used for simultaneous measurement of both Seebeck Coefficient and Electric Resistance (Resistivity).
- The sample holder uses a special contact mechanism for easy sample preparation and permits measurements of high reproducibility.
- V-I plot measurement can be made to judge if the sensor is in good contact with the sample.
- The system allows fully automatic, software controlled measurements with pre-defined temperature and measurement profiles.
- Measured raw data is stored on disc and can be exported in multiple data formates for post processing in Microsoft Excel or Origin.
- System comes with Constantan Reference incl. tables and certificate.
|Temperature range:||Basic unit: RT to 200°C*
Cryo option: -160°C to +200°C*
|Principles of measurement:||Seebeck-Coefficient measurement range: 0 to 2.5 mV/K – Temperature gradient up to 10K
Seebeck Voltage measurement: range +-8 mV
|Atmospheres:||Inert, reducing, oxidizing, vacuum
Low pressure helium gas, recommended
|Sample holder:||Integrated PCB Board with Primary and Secondary Heater|
|Sample size (Seebeck):||L: 8 mm to 25 mm; W: 2 mm to 25 mm; T: thin film to 2 mm|
|Sample size (Resistivity):||L: 18 mm to 25 mm; W: 18 mm to 25 mm; T: thin film to 2 mm|
|Heating rate:||0.01 – 100 K/min|
|Temperature precicion:||±1,5 °C oder 0,0040 ∙ | t ||
|Electric Resistivity:||10 nOhm|
|Thermovoltage:||0.5 nV/K (nV = 10-9 V)|
Make values visible and comparable
The powerful, Microsoft® Windows® based LINSEIS thermal analysis software performs the most important function in the preparation, execution and evaluation of thermoanalytical experiments, in addition to the hardware used. With this software package, Linseis offers a comprehensive solution for programming all device-specific settings and control functions, as well as for data storage and evaluation. The package was developed by our in-house software specialists and application experts and has been proven for years.
- Automatic evaluation of the Seebeck-Coefficient and the Electrical Conductivity
- Automatic control of sample contacting
- Creating Automatic Measurement Programs
- Creating temperature profiles and temperature gradients for the Seebeck measurement
- Real-time color rendering
- Automatic and manual scaling
- Representation of the axes freely selectable (e.g. temperature (x-axis) versus delta L (y-axis))
- Mathematical calculations (e.g. first and second derivative)
- Database for archiving all measurements and evaluations
- Multitasking (different programs can be used at the same time)
- Multi-User Option (user accounts)
- Zoom options for curve cuts
- Any number of curves can be loaded on top of each other for comparison
- Online Help Menu
- Free labeling of curves
- Simplified export functions (CTRL C)
- EXCEL® and ASCII export of measurement data
- Statistical trend evaluation (mean value curve with confidence interval)
- Tabular expression of the data</li>
Application example: Evaluation acquired data through linear regression
Seebeck voltage/temperature gradient (blue) measured while sweeping gradient heater power together with the linear regression (red).
Seebeck coefficient is determined by the slope of the linear regression.
Application example: Data evaluation
By this method the Seebeck coefficient is measured relative to Alumel. In order to calculate the absolute Seebeck coefficient Platinum is measured relative to the Alumel wire over temperature.>> Application
Application example: Seebeck coefficient vs. temperature
Seebeck coefficient measurement example of constantan.