The ac conductivity decreases on 1 wt % doping than the undoped one. But when it is increased to 3 wt %, it increases more than the undoped one. Can anyone give the explanation or reference?
Dear Dr. Ghosh
A.c conductivity is observed when dielectric loss occurs due to lag of polarization with respect to a.c. field applied. The frequency range and frequency dependence of dielectric constant and loss are important to know what type of polarization is responsible for a.c. conductivity. Unless these details are known, the effect of dopant concentration on a.c. conductivity can not be explained. Please see whether you get similar behaviour in d. c. Conductivity. Different dopant may also have different effect on d.c. and a.c. conductivity.
Dear Ghosh,
I agree with Dr. Kumar, additionally 1wt% you supposed to have added,but it does not mean it actually doped, it is too less to explain, I assure you when you will repeat including synthesis your result may be as for 3wt% , try at 2wt% too only then some trend can be visible.
If what you have observed is real, this means that you have at least 2 mechanisms competing with each other, the 1st one corresponding to the matrix, the 2nd one induced by the dopant. But I agree with former answers that you have to confirm this with more data, as only 2 points may mistake you if only one measurement can't be reproduced.
Alain
I fully agree with the observations and analysis of Alain Celzard
You have a critical amount of dopant which is decreasing the conductivity (whether dc or ac), and beyond the critical amount the conductivity goes up. This is possible, and largely depends on the dopant in host (ZnO).
You have not revealed the dopant to fully analyse the cause. It depends on the Valency state, the ionic radius of the dopant and its substitution into the host ZnO lattice.
In dc measurements your conductivity will decrease and resistivity goes up.
In ac measurement your dielectric loss (tan delta) should go down at the critical content of your dopant (1 wt %).
there are two competing mechanisms.
Maybe the dopant is compensating for the oxygen vacancies which can cause the conductivity, or restrain the formation of the oxygen vacancies upto the critical amount. Beyond the critical amount, the dopant substitution mechanism needs to be analysed, in order to answer the question why the conductivity is going up.
such kind of the results have been observed in many other ceramic compositions which indicate a critical amount of the dopant is effective for reducing the conductivity.
K. Sreenivas
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