Negative dielectric loss was observed in the sample at higher temperatures for all frequencies. Dielectric constant has a sharp anomaly before this temperature and we did not observe any negative capacitance . Can anyone explain the significance and physics behind this?
Dear Venkat,
Without knowing the test arrangement, some possible reasons:
-At higher temperatures the conductivity of the material increases and if the conductivity is enough high, the test circuit becomes inductive and your equipment displays negative loss factor and capacitance.
-Breakdown in material also increases the conductivity and you can see similar results.
DC resistance measurement at higher temperatures can help.
There are some difference in loss and loss factor. I hope you are talking about loss (is negative). It means effective conductance is negative. Of course it is possible that it may be behaving as an inductive circuit. However, I hope it is likely that some how instrument is not able to read the sample characteristics as such. If you upload dielectric spectrum with name of the instrument with which it is being measured a definite conclusion can be made. You can go through the following paper and if needed we can discuss
An impedance model to improve the higher frequency limit of electrical measurements on the capacitor cell made from electrodes of finite resistances, Ravindra Dhar, Ind. J. Pure & Appl. Phys., 42, 56-61, 2004.
If you measure a negative loss factor it may also be the result of a 'low-quality' reference capacitor. Usually these devices are insulated by a compressed insulated gas, eg. SF6, which have a low but not an infinite small gas conductivity. If the electric conductivity at AC voltage of your DUT is smaller than the one or your reference capacitor, then you measure a neg. loss factor.
I observed this effect with low conductivity insulation fluids myself. I am therefore in the process of building a C_ref myself. When I tested the prototype versus a standard C and measured also a 'neg. loss factor' I know that I am on the right way for 'precise measurements' with my device.
Ravindra Dhar thank you, the explanation of inductive circuit is helpful.