If this phenomenon is experimentally confirmed by the measurements, you can try to explain it considering actually two "phases" with different electrical conductivity: the bulk and the grain boundaries themselves. Obviously, in your case, the grain boundaries are more conductive than the bulk (and, therefore, increase in grain size causes decrease in overall material conductivity). Now, you need to study this matter experimentally, namely: to investigate the GB atomic structure, to measure their electrical conductivity, etc...

This is very common phenomena known as pulverization which creates micro cracks in the medium result in increase in resistance and decrease in particle size . you can Compare the SEM before and after related to particle size in cycling.

Thank you Mr Thomas Breuer for your quick response... The compositions studied are single phase perovskite oxides.

Thank you Mr Alexander for the answer. This behaviour is found from the experimental data obtained in the four-probe conductivity measurement of the samples. I would be glad if any references can be provided regarding this discussion.

Thanks in advance.

Thank you Mr Dhananjeyan Manikka for your response. Can you provide any supporting references in this perspective.

Thanks in advance.

To chelluri you can read some metal hydride material specially AB2 alloys which gave 125% expansion pulverize heavily and it was stabilized by adding some selective material . you can also stop expansion and contraction in your system with suitable material will lead to very high stability. Ref. papers -Available in sciencdirect

Dear Chelluri,

I am here assuming your sample is phase pure.

What I guess your materials conductivity is electronic nature (or may be mixed ionic) thus as the grains get develop and densification occurs its electronic conductivity will reduce. While porous and well connected grains give higher electronic conductivity. It can be explained in term of dihedral angle observed which basically lead to competitive variation in Grain boundary energy and surface energy.

Thank you Mr.Pardeep for your answer.

it could be also due to the growth mode. Larger grains could be segregated up to a certain thickness or you could be in a Volmer Weber growth mode... Is it really the grain size that gives this effect or is it thickness? Can you do some kind of surface characterization like AFM to check if there is a change in roughness between these films?

Thank you for your answer Mr.Mihai Gabureac.

Dear sir,

these samples studied were not films. These are sintered bar samples and conductivity measurement is done by four probe method.

Dear Researchers

Kindly comment on how electrical mobility depends upon the grain size of ZnO THIN FILMS

This dependence is best described by a model, brick-layer model (BLM) for grain sizes that take into account space charge layers along the grain boundary. Due to the segregation of space charges of point defects, the ionic partial conductivity decreases. As a consequence, the electronic conductivity should increase with the decrease in grain size for positive space charge regions and vice versa. Article Grain Size Dependence of Electrical Conductivity in Polycrys...

Please, read this paper for this question.