I am trying to determine the carrier concentration and mobility of La and Zr substituted bulk BiFeO3. My specimens are in a square/rectangular shape with thickness 0.6-0.8 mm and length/width of less than 10 mm. I have made electrodes at the four corners using silver paste. But the Hall measurement is giving data that is highly unreliable; the voltage values obtained in Van der Pauw method is inconsistent. Even successive measurement runs on the same sample without changing anything at all, is showing completely different results. A sample result is attached. What could possibly be causing this behavior and how can it be overcome?
Could you say more information about contacts deposition? What material (metal) did you use for that? May be such different Hall results can be attributed to weak contacts adhesion with your material. It would be useful try to deposit other contacts.
Contacts were made using silver paste/paint. After applying the paste the samples were heated at 350 C to get good adhesion.
May be you should try to deposit metalic contact by a vacuum sputtering or a chemical deposition and then fix Cu wires by silver paste/or by soldering?
The contact between Ag paste and BiFeO3 may not be ohmic, maybe it is Schottky.
Thanks for the answers.
Here's the thing.I have already measured I-V curves of these samples using the same silver paste (in a sandwich capacitor structure) and the resistivity does not change upon reversing the polarity of the applied voltage. I think that proves that an ohmic contact is formed between Ag paste and BiFeO3? Please corrct me if I am wrong.
The shape of the I-V curve is linear (that is I~V^n, where n is one) ? What the range of voltages was applied? Can you share the IV chart?
There are several criteria for ohmic contacts, only one of them is a linear IV characteristic
Here are two J-E curves belonging to two different compositions. The hall measurement for BLFZO-0 is given in original post and for BLFZO-2 I have attached another picture. As you can see the hall measurement for both compositions show inconsistencies. Note that J-E for BLFZO-0 does not have slope=1 in the log-log plot but the behavior is same regardless of voltage polarity meaning no diode like effect is being observed.
Because of using same material for contacts, the polarity may not be observed. On the other hands, BiFeO3 is magnetic materials. For this type materials, anomalous Hall effetc can occur. So the magnetization effect on total resistivity shoul be take into account [1]. Could you consider this effect?
[1] http://escholarship.org/uc/item/81n084n9#page-70
Well the anomalous hall effect might be present in BiFeO3, that's something I haven't looked into yet. But the fact remains that these measurements were carried out multiple times on the same sample - sometimes without even touching the connectors at all - but they still didn't give the same result. The variation was to an extent such that even the polarity of the hall coefficient was found to be reversed on subsequent measurements.
- Badges
- Science topic