Impedance
Electrical conductivity and impedance spectroscopy measurements
The electrical conductivity is determined by a modified four point technique (separate measurement of U and I) with two electrodes. The sample is clamped between these two platinum electrodes and the contact between sample and electrode is enhanced by a platinum paste. The measurements can be done within a frequency range of 20 Hz to 1 MHz. For the dc conductivity determination, only the data near 20 Hz is analyzed and in case of the impedance spectroscopy the whole frequency range is used. Within the used sample holders solid samples with dimensions of about 5 mm x 5 mm x 20 mm can be measured between room temperature and T = 1375 °C. The temperature is determined by a type-S thermocouple located at a distance of about 3 mm from the sample position.
Additionally, the gas atmosphere can be controlled by a gas mixing unit and therefore the oxygen partial pressure can be set to a desired value. The atmospheres can be mixed from following gases: oxygen, nitrogen, carbonmonoxide, carbondioxide, argon and hydrogen.
The oxygen content is measured by an oxygen sensor which uses a EMF-cell. In our laboratory there exist two identical furnaces and it is possible to measure two samples in parallel. This is established by a four channel switch, which shares the LCR-meter between the two sample holders.
Sampleholder
Electrical conductivity relaxation measurements (ECR)
After a sudden, step-like change of the applied oxygen fugacity, the time evolution of the electrical conductivity is measured. From this data, the oxygen incorporation or evaporation of the sample can be observed. These results are compared with diffusion limited or reaction kinetic limited theory functions and give information about the diffusion rates, the reaction velocity and the rate determing step.
Instruments:
- HP precision LCR meter 4284A (f = 20 Hz .. 1 MHz)
- Telemeter MTS 4 channel-hf-relais (switching between sampleholders)
- MKS multichannel gas flow controller 647C with 4 mass flow controllers 1259C
- Eurotherm temperature controller 900 series
- 2 horizontal tube furnaces with T(max) = 1375 °C and integrated EMF-cells
- External oxygen sensor Metrotec AN15-N
- Keithley DMM 2000 (U of the thermocouples and the EMF)
- T = 50 °C thermocouple reference point (ice-point) for type-S thermocouples
- NI LabVIEW and turbo pascal based software
Responsible:
Content Manager
Feedback to s.dlugocz@tu-braunschweig.de
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