Why cant u anneal the films in oxygen environment for some time and do immeadiately the measurements. This is just the guess for possible conductivity.

What about your old samples? Do they still show the P-E loops as before?

Dear Sir, 

Thank you very much for reply. Sorry for late reply. I don't get notification for this. Now also I am able to get  well saturated P-E loop on the old samples.  But new samples are totally conducting.

Clearly you have a problem with the film preparation. Only you could check if every parametet was carefully reproduced for the preparation of films and also for the target preparatoin.

Increase Bi content just a bit over stoichiometry (2%) and anneal before top electrode and after. You have non stoichiometric grain boundaries and surface-meaning oxygen vacancies. Now, a bit of Cr or Dy (1%) may oxidize your GB and Surface. But, BiO is a fast diffuser and diffuses out, leaving such vacancies. Also, it may form a layer at the surface which is a Bi/Pt (electrode) alloy. So, you must increase oxygen flow and anneal before and after electrode deposition. The BiO will react with the oxygen strongly and maitain stiochiometry - you will get better films.

Dear Sir,

Thank you very much for your suggestion. I will surely try this. 

BFO is considered to be quite a leaky material. Don't know the exact reason what cause the conductivity. In the literature many dopants hve been attempted both in bulk and thin film form, and till now the high leakage problem in the case of BFO has not been solved comfortably.

there can be loss of bismuth, and this can cause oxygen vacancies. doping to some extent will help, but does not show significant improvements. This leakage problems is currently being investigated by many researchers.

In your question please make the correction, a conducting sample will show you a circular loop. If you put a piece of paper you will see a straight line typical of a linear dielectric.

A highly resistive sample with asymmetry in the crystal structure will show you the typical P-E. hysteresis loop. 

To see ferroelectricicty you must have the composition (stoichiometry) correctly controlled, and sencondly you should have the right crystallographic phase. If any or both these things are missing, you will not be able to measure the HY loop.

somewhere your composition control is getting out of control. If you solve this problem you will be able to regain your previous made films.

Also look at the laser pulse shot energy. Try to re calibrate your laser output. this can disturb the stoichiometry of the ablated specie. As you said you changed the target, but how about laser deposition conditions.

K. Sreenivas

Dear Sir,

Thank you very much for your answer. If I measure today my old optimized films show high-quality P-E loop. But after one year using same target I could not able to achieve P-E loop at any condition. I tried with changing Pressure, substrate temperature, new PLD target, new oxygen gas cylinder, energy density. On suspicion, I also tried by change vacuum gauge but it showing same pressure as old. After all this  I could not get good quality films. I think my target get degraded or something terrible might  have happen to PLD chamber. The sample color also changes drastically.  Do you have any suggestion over this. Your help in this regard is highly appreciated. 

Regards,

Jayant

You findings confirm what people have experienced since a long time. 

Target surface composition changes after a few ablations. Normally one removes the target, scrapes it off, and obtain a smooth surface, mount it back and start ablating it again.

Use the same old conditions, and with a fresh target surface, (preferably every time) if possible, then you should be able to reproduce the properties in your deposited films also.

K. Sreenivas

Dear Sir,

Thank you very much for your  suggestion. I will surely try this before taking next deposition. I hope I will get good quality thin films.