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Seebsys - Combined Seebeck coefficient and resistance measurement system description

SeebSys

The SeebSys is a system for automated measurements of Seebeck coefficient and electrical resistance on small samples at high temperatures and under various atmospheres. The full system consists of sample holder, furnace, measurement instrument, power supply and internal heater, computer and measurement software. All instruments are controlled by software running on the computer.

SeebSys is no 'simple push-button-get-results' instrument. It is a modular system allowing the end user to tweak any aspect of the setup to their specific own needs. This means steeper learning curve, elevated need for user involvement and skill but as said, offers great flexibility as well.

Brief system description

Sample (DUT) is mounted in ProboStat sample holder with electrodes, thermocouples and resistance heater. The sample holder is inserted into a furnace. The software instructs the furnace to reach target temperature, and controls the measurement instruments and the power supply for connected to the internal heater

The internal heater is used to alter the gradient over the sample and the multimeter is used to measure sample voltage, thermocouple voltages, sample resistance and thermistor resistance at thermocouple cold junction. The software automatically calculates all relevant properties and takes predefined actions to automate the process.

 The system can also be expanded for fully automated Van der Pauw measurement method on disc samples.

Specifications for individual components

ProboStat™

ProboStat is a sample holder with 16 electrical connections to the sample area. Standard electrodes are platinum and thermocouples are S-type. The hot zone area of ProboStat is built with high purity alumina parts. Inside volume can be filled and flushed with desired atmosphere (inert, oxidizing, reducing, corrosive) or pumped to low vacuum.

The sample is suspended between two current electrodes in vertical position using a spring load setup. Two additional voltage probe electrodes for 4-point resistance measurements are applied to the sample.

ProboStat™ offers flexibility and expandability in terms of alternative methods for other types of measurements (additional parts required): Conductivity vs T, pO2, pH2O, etc., impedance spectroscopy, Dielectric properties, loss, etc., Disk, van der Pauw, and bar geometries, 2, 3, and 4 electrodes, Ionic transport number, Proton transport number, I-V-characteristics, Fuel cell components and single cell testing, Electrode kinetics, H/D isotope effects, Electrochemical pumping, gas permeation and electrocatalysis with gas analysis (e.g. GC or MS) on outlets, Sensor testing, and so forth. See http://www.norecs.com/index.php?page=11&p=all for references.

Furnace

Vertical split furnace specially designed for ProboStat, 1700W, single phase, maximum temperature for the standard version 1200°C

Instruments

Digital multimeter and digital power source are built into one encasing with connections on the back side. The instruments communicate with the computer through USB cable. The BNC cables carrying sample signals connect to the ProboStat sample holder.

The digital multimeter with signal switching under computer control will continuously measure all required properties automatically:

  • 1 x Sample resistance with forward current (4 electrode method)
  • 1 x Sample resistance with reverse current (4 electrode method)
  • 1 x Thermistor temperature for cold junction compensation (2 electrode method)
  • 2 x Thermocouple voltage (2 electrode method)
  • 1 x Sample voltage (2 electrode method)

The software will convert and calculate all necessary steps to display Seebeck coefficient and electrical resistivity. The thermo voltage in the platinum electrodes over temperature gradient is automatically subtracted from sample voltage.

Computer and software

A pre-configured laptop computer with latest Windows operating system and all required cables to connect to the devices. The included software allows control of all aspects of the experiment:

  • Furnace heating and cooling to desired temperature. Reading and plotting the general temperature of the experiment
  • Power source control for internal heater to achieve separate gradients automatically in same general temperature zone
  • Constantly reading (and plotting) the temperatures at the top and the bottom of the sample
  • Constantly reading (and plotting) the sample voltage
  • Correcting for the Seebeck voltage over the platinum wire for the same gradient the sample is exposed to
  • Constantly reading (and plotting) the sample 4 point resistance, automatically eliminating the effect of the Seebeck voltage over sample.
  • Exporting the data to text file

Optional: Laser printer.

 

Specifications

 

Sample size

Bar shaped samples are limited to maximum of 10 mm cross section. The maximum length of the sample is about 50 mm. We recommend minimum of 5 mm cross section and 30mm length. The voltage electrode contacts can be point contact, per face contact or wrapped fully around the sample when oxides form on sample surface.

Smaller samples are possible, but on the expense of measurement accuracy:

  • Regardless of the sample size the sum of all measurement errors remain same. With small or tiny sample the 'error to real value' -ratio is always worse than for a big sample.
  • Mounting electrodes on a small sample is more challenging: For the four point conductivity measurement it is required to establish two voltage electrode contacts along the bar, and to define the exact distance between them.
  • For the Seebeck coefficient measurement a temperature gradient needs to be established. The smaller the sample the smaller the possible temperature gradient is.

Please refer to chapter ‘electrode preparation and measurement accuracy’ for more details.

Thin film samples

Same measurements may be possible for thin films on non-conductive substrates, but sample and electrode preparation will be more critical than on normal samples. Please consult NorECs AS for details (please explain your thin film and substrate in detail)

As preliminary info

Millimeter scale wires can be hard to connect to less than micrometer thick thin film in a way that can be properly measured (since the distances are important). For best results it is often required for the user to add intermediate electrode between the wire electrode and the thin film, for example as described in this picture:

These intermediate electrodes need to be prepared by the end user by means of for example sputtering, vapor deposition, painting or spraying.

Atmospheres

The sample holder cell has two ingoing gas connects and two outgoing gas connections allowing for example measurements as function of oxygen partial pressure (gas supply system not included).

Vacuum definition: The leakage rate of air into the cell is typically 0.01 mbar/min.

The standard version of ProboStat can be used with oxidizing, inert, and reducing atmospheres, as well as wet (or dry) gases.

Optional for atmospheres

The stainless steel version can be used also with many corrosive gases, such as ammonia, wet acidic exhaust gases, etc.

The system can be equipped with an enclosing high-temperature steel tube the cell can operate at high pressures (up to 15 bar of air or inert gas) but this requires use of another type of furnace.

 

Instruments

Digital multimeter

 

Property

Value (24 hours)

Value (1 year)

 

Voltage resolution

10 nV

 

 

Voltage accuracy

10 ppm of reading +/- 1.2 µV

37 ppm of reading +/- 1.2 µV

 

Resistance resolution

1 µΩ

 

 

Resistance accuracy

9 ppm of reading +/- 0.14 mΩ

72 ppm of reading +/- 0.14 mΩ

More accurate versions on request.

Power supply

Programmable 20V / 5A / 100W power supply

Other considerations

Electrode preparation and measurement accuracy

The volume specific conductivity is calculated from raw data and the accuracy of the result depends on user provided measurements of sample cross section and voltage electrode distance.

The need for possible on-sample electrodes depend heavily on the user and sample specific challenges. In many cases it is enough just to spring load and tie the electrodes provided to the sample, but in some more challenging cases the user needs to prepare on-sample electrodes by screen printing, hand painting, sputtering, sintering a piece of thin Pt wire or by any other suitable method. The manual has examples on sample preparation and NorECs is happy to provide help on any user specific challenge.

Alternatives

Ulvac ZEM-3

Linseis LRS-3

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