Sandip, have you tried to make the contact directly on the pellet using silver ink? I have a colleague who have studied the electrical properties of new materials for varistor aplications. He usually makes the contacts on both sides of pellets by applying the silver ink directly on the copper wires ends placed on the pellet surface (previously cleaned). As far I know, the experiments have been successful...

Hello Sandip,

Silver paints vary in quality so much that it is hard to rely on as you have found out. You can try In-Ga, which is a mercury-like liquid at room temperatures. In place of silver paint, you can dip probes in In-Ga in a way Walter Folly has suggested.

Good idea, Kanad!!

Sandip , I mostly use silver paste , but how to control thickness is tricky and need some time and experimentation and Kanad's answer is useful for you.

What about 4-point probe techniques - if you apply two contacts on each face of the pellet (eventually using the same silver-ink drop for both contacts, then you can measure the current and the voltage with two individual pairs of connections, and the influcence (ohmic drop etc) of the contacts are minimized. Good luck

Ag paint might be a good idea but it is better to make a thermal treatment.

At least, in an oven at 200°C. Ideally a short treatment at 600-700°C.

Over this temperature, Ag electrodes start to degrade.

Au or Pt inks are also good choice but they need high temperature tretament:

typically 800-850°C for gold, 900-1000°C for Pt (during typically 0.5h-2h).

Many providers:.

Electroscience is one of them, metallor etc...

In all cases you can verify the quality of the electrode by measuring laterally the

resistance on one given side of your sample with two probes connected to multimeter. This does not allow you identifying if the material/interface is good but that the lateral resistance is minimal (typically less than 1 ohm). Then, once the lateral resistance is much smaller than your sample resistance, you can come with a punctal wire/contact on the electrode.

You havent mentioned the dimension of the pellets & its electrical nature. If its conductivity is too low it is difficult to do electrical characterization despite you use Ag paste or something. You can use keithley/agilent source measure unit instead of four probe. Otherwise you can deposit on a substrate using sputtering/PLD in nanoscale and measure easily using four probe

Thank you all for your helpful answers. I am trying to figure out what can be the best possible way. The Ag film on both sides of the pellet is coz of conducting purposes. Now I sandwich the pellet between copper plates after putting a thin silver film. Now is it advisable. Is there a way that I can take a contact (say a copper wire) from the two surfaces of the pellets. If so how?

Kannad Sir I will try out your Suggestion as well. Its seems to be a good idea. Ravi sir my material is SnO2. Conductivity is appreciably high. I am infact using a Kethley Electrometer for the electrical characterization. But making contacts on both sides of the pellet is my main concern. As putting the pellets within copper plates for probe contact is a doubtful issue, thats what I felt.

Help please..

Walter Sir how is the copper wires ends placed on the pellet surface? Is it pasted?

Supposing you have constant thickness plate like pellets and you want to place two contacts on the faces of the samples. Try making two frames with soldered contacts. The frames are then fixed on the sample's surface with a mechanical pressure based method. |The silver paste goes between the metalic frames and the probe. The pressure rests applied all the time during the measurement. a set of wires solered on the frames are your electrodes. The frames are for constant contact surface on all your samples and the constant pressure is for safety your contacts (also for good alignement). The frames can be machined from 0.1 mm thick copper foil , with ring - like (or quadratic) shape.

If you are using keithley, then the sample holder will give you more better results than any other methods you follow. We have tried 7 years back and without specific sample holder for keithley (which can be purchased separately) the results may not reproducible. Of course the sample holders are costly. Try the method given by Mircea pop. We have done similar approach seven years back.

Thank u

We measure the resistivity in PPMS using the pellet by four probe method. Two contacts for current flow and two contacts for voltage application. The contacts are made with conducting Ag paste. Very thin Copper wires are used for making contacts.

thank u Dinesh ji.. can u pls tell me how are those copper wire contacts pasted on the surface of the pellets?

I do not know what kind of arrangement you people have in your lab to place the pellet for the measurement. We have resistivity puck and pellet is placed in the space provided within that. Then we paste the copper wires on the respective contacts (current and voltage) on the puck just keeping wires straight.

i m not getting the supplier for In-Ga in India. can any one help me out from this problem.?