Barrier is a type of shield, but only biotics use them. The blue bar will specifically say barrier instead of shields. You, or a squad member, have to deal the finishing blow to the barrier bar with the Warp power 25 times to earn the achievement. Asari (Eclipse mercenaries) and occasionally krogan will have them. The Collector’s, assassins and harbingers specifically, also use them quite often. Thane and Samara’s recruiting missions both have a good amount of biotics that will use barriers for you to remove.
Note: Find a group of enemies using barriers and destroy them all using warp. Then reload your checkpoint. It will keep your progress and you can repeat the process until you get the achievement.