Yes. Its called an EverStone and it Prevents The Pokemon That Is Holding On To It From Evolving.
(This is for the person who posted this answer (originally including a derogatory slight towards the person asking the question):
Congratulations. You are under the impression that you are better at *Pokemon* than another person. You are definitely going to die happier and more accomplished than the rest of us...)
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There is 2 ways to stop evolving: During the Pokemon's evolution keep pressing the B button to stop the evolution, also have the Pokemon hold the item everstone no matter what level the Pokemon is it will never evolve if it's holding that item and if it evolves during trade if it's holding the everstone it still will not evolve.
All you get is an evolution item, like metal coat or dragon scale
use a pokemon that is a higher level than the pokemon you are facing and use "mean look".That way,the pokemon can't escape.
When you buy or win an evolution item, you have to go to "My Pokemon" from the Trainer HQ tab, scroll down to the Pokemon you want to evolve, and look at the far right, there should be an option that says "Evolve me!" Click that, then click the "Evolve!" button on the next screen. Hope I helped!
To Stop Evolution:Tap the B Button Repeatedly until Evolution stops (While Evolving)Make your Pokemon hold an Everstone (Does not Evolve while Hold)Note: Trading Pokemon that Evolve can not be stopped.