Is there any correlation between the frequency range and the overall system resistance?
54 views
Skip to first unread message
erricoilfico
Jan 26, 2018, 7:03:46 AM1/26/18
to Impedance Spectroscopy
Dear all,
I'm doing some impedance measurements on titanium samples in an alkaline solution, actually I'm interested in determining the electronic properties of the titanium oxide before and after anodic polarizations.
According to literature a suitable equivalent circuit is composed by two nested (RC) circuits, lower frequency being attributed to the response of the inner compact oxide layer, while the high frequency response should be correlated to the outer TiOx porous layer.
I'm having very big issues in the fitting of the experimental data... I managed to fit some of the "before anodic polarization" spectra (but not all of them even if they should be very similar) and none of the "after anodic polarization" spectra. Especially in these latter case i got some very huge errors conserning the resistance of the inner layer.
I run my test in frequency range of 10^5 to 10^-2 Hz, and given the fact that even before the anodic polarization the inner layer resistance resulted to be very high ( 10^6 - 10^7 Ohm.cm) I was wondering if the the fitting issues that I'm experiencing could be in some way correlated to the frequency range that I'm using.
In other words the question is: is there any correlation between the system resistance and the optimum scanned frequency range? Is it possible that a highly resistive system measured at not enogh low frequency results in hard-to-fit spectra?
Many many thanks to whom will answer
Kind regards
Enrico Volpi
I'm doing some impedance measurements on titanium samples in an alkaline solution, actually I'm interested in determining the electronic properties of the titanium oxide before and after anodic polarizations.
According to literature a suitable equivalent circuit is composed by two nested (RC) circuits, lower frequency being attributed to the response of the inner compact oxide layer, while the high frequency response should be correlated to the outer TiOx porous layer.
I'm having very big issues in the fitting of the experimental data... I managed to fit some of the "before anodic polarization" spectra (but not all of them even if they should be very similar) and none of the "after anodic polarization" spectra. Especially in these latter case i got some very huge errors conserning the resistance of the inner layer.
I run my test in frequency range of 10^5 to 10^-2 Hz, and given the fact that even before the anodic polarization the inner layer resistance resulted to be very high ( 10^6 - 10^7 Ohm.cm) I was wondering if the the fitting issues that I'm experiencing could be in some way correlated to the frequency range that I'm using.
In other words the question is: is there any correlation between the system resistance and the optimum scanned frequency range? Is it possible that a highly resistive system measured at not enogh low frequency results in hard-to-fit spectra?
Many many thanks to whom will answer
Kind regards
Enrico Volpi
Jacopo Remondina
Feb 27, 2018, 11:50:43 AM2/27/18
to Impedance Spectroscopy
Dear Enrico,
it would be helpful to see one of your spectra so to better understand the problem. Anyway, a good hint that you're monitoring enough slow frequency is the fact that your semicircles close on the real (X) axis, or, in other words, that the immaginary part of your data become negligible. Same idea is still valid for high frequency limit, but here is more difficult (you will always see higher frequency contributions).
Best regards,
Jacopo Remondina
it would be helpful to see one of your spectra so to better understand the problem. Anyway, a good hint that you're monitoring enough slow frequency is the fact that your semicircles close on the real (X) axis, or, in other words, that the immaginary part of your data become negligible. Same idea is still valid for high frequency limit, but here is more difficult (you will always see higher frequency contributions).
Best regards,
Jacopo Remondina
Reply all
Reply to author
Forward
0 new messages