It is reported that several important pervoskites like SrTiO3, BaTiO3 have surface layers that are structurally different from the interior of crystal. Further, it can show transition similar to that of crystal at some different temperature. Can anyone please tell me how to differentiate the grain boundaries, grains, and surface layer contribution in complex modulus spectrum i.e., plot between M" vs M'?
there are many old paper dealing with surface layer effects in polycrystalline ceramics and single crystals.
When you are preparing powders of varying size, by cryshing them, later compacting them to form ceramics, you will form, grain and grain boundaries. Later when you polish ceramics to a certain thickness, by mechanical grinding, lapping, and polishing you can always form defective surface layers due to mechanical friction which generates a lot of heat. Same may apply to single crystals in case you are trying to mechanically grind/lap/polish them to a given thickness.
these surface layers are dead layers which can have some lattice defects, or intrusion of impurities. Their electrical properties can be totally different from the bulk of the polycrystalline ceramic/crystal underneath the dead surface layer. For exapmple the dielectric constant, tan delta, dc conductivity can be different in the surface layer region, and moreover the thickness of the surface layer that is formed can also influence your results.
You should there try to anneal them out. After the final polishing, removing all the residual impurities such as your polishing/lapping materials, grease, and particles. A high temperature anneal in the right ambient may reconstruct/transform your dead surface layers. therefore a lot of care should be taken when you are trying size your samples.
I would say simple dielectric dispersion analysis where you study the response of the measured dielectric constant with frequency can reveal a lot of information. Later you can also do the complex impedance analysis, which can reveal the effect of surface layers (if any). I am not sure if the modulus spectroscopy will help you much in this regard to understand the surface layer affects.
K. Sreenivas
Thank you sir for your detail explanation. I did the dielectric dispersion analysis, but unable to differentiate the surface layer contribution from grains and grain boundaries contribution. Please tell me how to differentiate using dielectric dispersion analysis.
Dear Bipul Deka,
inform us please, about exp. details (and give a plot of your initial results). A relatively high (contact) res. Rc may hide most of the infos (below Rc value) you are looking for.
Dear Samaras Sir,
In which region of frequency the effect of skin layer will be noticed?
Dear Bipul Deka,
the skin effect may appear at the higher frequency part (>50kHz). Give us, please, a plot of your initial results.
Dear Bipul Deka,
your results seem to have a contribution from the electronic circuits (Zecthat is parallel to your specimen's Zs) of your meas. system and some cap. Zsh from the specimen's holder, also. You may try to correct the graphs of Zmeasured (Zs//Zec//Zsh). in order to get your sample properties Zs , only, i.e. the material properties.
Notes for Zec : 1) Check your meas. system specs for Z-input , or e-mail to manufacturer (better) for Z-input. If neither works then,
2)measure (at least one) a simple commercial Resistor R (500kOhm to 1MOhm, p>0.5W) and find a hint for the (model) corrections.
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