Effect of thiourea on grain refinement and defect structure of the pulsed electrodeposited nanocrystalline copper

► Grain refinement is due to change in nucleation, growth and defect structure. ► Nucleation mode is changed from instantaneous to progressive with thiourea addition. ► Growth is inhibited by segregation of thiourea at the grain boundaries. ► The copper electrodeposit prepared without addition of thiourea reveals dislocations. ► Grain refinement is due to predominant formation of twins in presence of thiourea.