There are many reports which say that oxygen vacancy in BiFeO3 ceramics arises due to bismuth evaporation (Volatile nature of bismuth) during high temperature synthesis.What may be the proper causes for which bismuth is volatile in nature?
Hi Abhishek, I guess this is primarily due to the very low melting point of bismuth which would give rise to a high vapour pressure when heated to high temperature during synthesis.
The answer to this is very difficult and comes down to the structural and electronic properties of the material. The melting point, boiling point, and volatility are all related because they relate to overcoming an energetic barrier to transition from a lower entropy state to a higher entropy state. This energetic barrier is smaller when the interatomic bonding is weaker (based on its electronic configuration, coordination number, atom size, etc). There is no single property that dictates boiling point or volatility but my guess for bismuth is that it interacts weakly with surrounding atoms because it's a very large atom with its valence electrons in the p-shell, and it probably has a low coordination number (though I looked up the crystal structure from 4 references and got 4 wildly different answers).
As for the above answer, the melting point is related, but is not the cause. For example, Al and Mg have basically the same melting temperature, but Mg is much more volatile. Boiling point is more related to volatility since it deals with the transition to a gas, but still is not the cause of its volatility, just another result of its interatomic bond strength.
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