In the Wikipedia article on crystallographic defects, a type of point defect known as an interstitial defect is described as follows:
Interstitial defects are atoms that occupy a site in the crystal structure at which there is usually not an atom. They are generally high energy configurations. Small atoms (mostly impurities) in some crystals can occupy interstices without high energy, such as hydrogen in palladium.
What is meant here by "high energy configurations"? If these defects possess a "high energy configuration", then it sounds like they would be difficult to come about? If so, then how do these defects come about (where do they gain the energy from to occur)?
I would greatly appreciate it if people would please take the time to clarify this.