High voltage feedthroughs allow experiments with ferro- and piezoelectric materials. We can deliver ProboStats with feedthroughs that tolerate >10 kV DC. The final tolerance in the sample compartment depends on the sample, pressure, atmosphere, and temperature. The high voltage feedthroughs can be fitted to new ProboStat base units; normally two of the normal outer chamber feedthroughs ("HC" and "LC") are replaced by high voltage feedthroughs, and the BNC connectors are replaced by a high voltage version. Cost is estimated to be ca. 600 USD higher than for the standard ProboStat base unit.
We can now deliver ProboStat in a version where 2 feedthroughs are of high-voltage type, tolerating up to 10 kV DC.
The final limiting breakdown voltage in the sample compartment may of course be further limited by the electrode and sample geometries, temperature, pressure and atmosphere, and the sample itself. We have tested the setup at various total pressures and temperatures using a 20 mm diameter, 3 mm thick alumina disk sample, and confirmed that the breakdown voltage follows mainly Paschen's formula. At atmospheric pressure the breakdown voltage is then limited to 5-9 kV DC by the distance between the electrodes. At elevated temperatures or lower pressures, the breakdown voltage decreases and plasma discharge arises. At further lowering of the pressure into the low-vacuum the breakdown voltage again rises (as predicted by Paschen's formula), and it is again possible to reach voltages exceeding 10 kV DC, also at elevated temperatures. This may be done by pumping on the normal base unit gas connections. For faster pumping it may be desirable to pump through a vacuum flange that can be attached to an open end enclosing tube.
Normally, it is the two outer chamber feedthroughs ("HC" and "LC") that are replaced by high voltage versions. The two corresponding BNC connectors are also replaced by high voltage connectors. Some changes from the normal ProboStat are done in the wiring of shields, but otherwise the remaining feedthroughs are left as they are in the normal ProboStat, so that one may use up to three thermocouples or use the cell much as a normal ProboStat for normal low-voltage measurements. We may add one or two more high-voltage feedthroughs to the outer chamber, or one to the inner chamber, at special order.
The feedthroughs are made with brass conductors in the cold end of the base unit, insulated with fully dense (AL23) 99.7% alumina tubes through the base unit, and with two layers of insulating high-voltage-tolerant plastic in the hexagon connection box. In the sample chamber, the brass wires are terminated in male mini-contacts, standing on a 2 cm length of the alumina insulating tube. Contact to the high temperature zone is done with detachable wires made of, for instance, Pt or Au, soldered onto female mini-contacts, and insulated in an alumina capillary. The mini-contact zone is covered with a slide-on wider alumina tube. As said above, this construction withstands >10 kV DC in air at atmospheric pressure at room temperature.
Samples and electrode contacts may be held in place by using our standard alumina-based spring-loads.
The high- voltage feedthroughs can be fitted to new orders of ProboStat base units. (Retrofit is possible, but we do not recommend it.)
Cost for a ProboStat with two high-voltage feedthroughs is estimated at ca. 600 USD higher than for a corresponding standard ProboStat, including male connectors to the high voltage external contacts and spare female mini-contacts for making custom electrode contacts. We can make electrode contacts from e.g. Pt, Au, or Ni at customer's request.
The high-voltage version allows polarization (poling) experiments with ferroelectric materials. It is compatible with connections and operations of for instance aixACCT Systems Gmbh.
The optical port that can be included in a vacuum flange at an open-ended enclosing tube gives possibility to access the sample with a laser interferometer. Other types of experiments enabled by the high-voltage feedthroughs comprise plasma electrodics (e.g. MS-studies of ion extraction from ionic conductors).
When using a thermocouple in a cell carrying high voltages, the thermocouple should be covered by the envelope alumina tube that we supply. This will prevent high-voltage discharge to the thermocouple.
Naturally, the user is responsible for all further precautions required to protect users and connected instrumentation toward possible high-voltage discharges.
