ionic Conductivity will increase or decrease if we decrease the size of grains(approaching nm) in solids?
Hello,
this is a complicated question that can not be answered straight forward. For instance, there has been an ongoing debate about the behavior of the oxygen-ion conductivity of YSZ and other rare-earth oxides on the nm-scale for around 20 years. To give you some insight:
- It always depends on the bulk and grain boundary conductivity of the specific material. Knowing your microstructure and morphology (grain-size distribution, texture especially in thin films, etc.) in detail you may estimate and even predict the overall conductivity (depending on which type of conductivity dominates)
- But, you have to be very careful interpreting data because having much more grain-boundary area available in nm-grained ceramics, your impurities (present in the material, especially at the grain boundaries) are also "better" destributed (much lower local concentration). This might have a severe impact especially on the grain-boundary conductivity that can change by several orders of magnitude.
- Furthermore, the complete conduction process may change if space-charge areas at grain-boundary play a crucial role and start overlapping as you approach a certain grain size.
The is much literature available about those different issues!
To answer your question in more detail, you will have to specify at least the type of material (better the detailed composition) and the type of ions you are interested in.
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