Located in Ch.2 before leaving for Banora Village. The Materia room is on the same floor as the training room so no moving floors. You must do this in Ch.2 If you dont its unattainable and requires a second playthrough.
Go in the materia room and talk to the scientist directly in front of you. Should have a orange talk option on him. If not go do the training room clears for Hojo then head to the materia room. The scientist will ask you for something give it to him then watch what they do with the materia. The achievement should unlock immediatley or when you start the next cutscene.