As everyone above has said, your loops are indicative of a lossy dielectric. Are you expecting ferroelectric behaviour ? ZnO is piezoelectric, but not ferroelectric. I believe your loops show that after doping, the conductivity may be reduced and permittivity may be slightly increased - but definitely no evidence of ferroelectric behaviour. This wouldn't seem to be the best way to characterize this material - I would recommend impedance spectroscopy.

Those are the typical PE loops of a lossy capacitor (parallel RC circuit). To analyze PE loops, try to have a look into the manual of the instrument you are using. By changing the dielectric constant and the resistivity of the ZnO, you can change the shape of the loop, which depends on the RC values.

Dear Rajagopalan,

Following the Lorenzo's comment idea, which is pretty good, the main characteristic of a elliptical PE loop is the low resistivity behavior of your sample (you have no resistance to saturate the charges under electric field). Since you doped it to reduce the current leakage, the charge motion under applied field, determined by dQ/dV becomes a hysteresis loop. Briefly, I would say you have to complement your measurements by doing a I-V curve, specially because the PE loop hides a lot of information about the fundamental behavior of the material (since it is a calculated loop, according the equation I inserted above).

If you wanna read something about this kind of measurements (specially if you are using the Radiant tester), you can check the link down below:

https://www.ferrodevices.com/1/297/files/Ferroelectric_Properties_and_Instrumentation.pdf

PS. I've checked the values of your data and it seems your measurements were not carried out using the same parameters (mainly because the values of Pr does't decrease with the increase of doping level systematically). I would suggest to be careful with the parameters of the measurements by using the same frequency and the electric field applied on the samples.

Best Regards,

1) What is the thickness of your sample (films/solid), this is not clear in your question, but looks like you have applied nearly 100 volts, but across what thickness.

put a small piece of thin paper (insulating) with proper electrodes on either side, and check what kind of PE loops is your system measuring.

2) put a sample which is a leaky insulator and check again what kind of loop is your system measuring.

3) Since you are doping ZnO with some dopant, do you any evidence of a non-centro symmetric structure formation to support the observation of any ferroelectricity in the prepared samples.

4) Hopefully you have calibrated your system with a good well known ferroelectric (film/ceramic/crystal), and were able to measure good saturating PE loops. This is just to ensure that there is no measurement system generated problems.

But systems a very leaky ferroelectric can also produce the typical loops which you have shown.

As everyone above has said, your loops are indicative of a lossy dielectric. Are you expecting ferroelectric behaviour ? ZnO is piezoelectric, but not ferroelectric. I believe your loops show that after doping, the conductivity may be reduced and permittivity may be slightly increased - but definitely no evidence of ferroelectric behaviour. This wouldn't seem to be the best way to characterize this material - I would recommend impedance spectroscopy.

You may find number of papers having similar P-E loop shape. But there are number of factors contributing to the P-E loop. You can find those in the related papers and also in the link given by Everton Bonturim.

To get information about the intrinsic ferroelectricity you should go for Remanent Polarization measurements.

P-E loops of ferroelectric material doesn't look like what you get.

Thanks

thanks Dr Andrew J bell for pointing out the inclusion of resistance in the film on account of doping. If possible ill try with impedanc spectroscopy. can you suggest some papers in this direction? thanks in advance

thnaks Dr Shreenivas for your answer. the thickness of samples were slighlty differnt from each other but were in the range of 600-1000 micrometer. the thicness was precisely measured with vernier caliper.

Ill check the paper test soon.

Also, regarding the ferro behaviour there are ample reports on that dopant and several papers have claimed a week ferroelectric domains is created after doping.

Journal of Advanced Dielectrics

Vol. 1, No. 1 (2011) 107
118

please read in detail the article cited above,

Best regard, Dr Calderón

Dear Rajagopalan Pandey

Fig (a) shows the Leakey behaviour of the material. This may be due to shorting of the electrodes or may be due to the material properties itself.

Fig (b) to (d) shows the change from Leakey loop to hysteresis loop. However, leakage is again high at higher fields. Only these loops cannot confirm the domain switching or ferroelectric behaviour.

Regards

Dr. Ajeet Kumar

You can refer this Manuscript may you can get some idea

1. These samples seem to be pellets. Which material you are using for the electrode?

2. A variation of dielectric constant with temperature can be tried as suggested by many.

3. A measurement of dc conductivity as a function of doping may be useful.

4. Which set-up you are using for the measurement. Do you have ample options of RC combinations. You can increase RC combinations so that you can get the optimum response at a suitable RC value.

Thanks all respected Prof. Got a lot of information.