Microstructural Defects and Their Formation Mechanisms in Ba_(0.75)Sr_(0.25)TiO_3 Epitaxial Film

Ba0.75Sr0.25TiO3 film was epitaxially grown on a(001) LaAlO3 substrate using single-target pulsed laser deposition.The microstructure of the epitaxial film was investigated by high-resolution transmission electron microscope(HRTEM),and the formation mechanism of microstructural defects was explored.It was shown that misfit and threading dislocations existed in the epitaxial Ba 0.75 Sr 0.25 TiO 3 film.Apart from the dislocations,two different kinds of antiphase boundaries,straight and zig-zagged,were observed.For misfit dislocations,they were formed due to the lattice mismatch between LaAlO 3 and Ba 0.75 Sr 0.25 TiO 3 which could dissociate into several partial dislocations.For the threading dislocations,it was found that their dissociation usually coexists with stacking faults.The formation mechanism of the antiphase boundaries is attributed to the terrace or step on the surfaces of LaAlO 3 substrate.If the nucleation site is just on the terrace,straight antiphase boundaries will be formed.However,if the nucleation site is not just on the terrace but a little far away from the terrace,zig-zagged antiphase boundaries will be produced.The results could shed light on the microstructural defects in other perovskite epitaxial films.