Epitaxial ${\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Ti}{\mathrm{O}}_3$ thin films grown on the (001) $\mathrm{La}\mathrm{Al}{\mathrm{O}}_3$ substrates with a ferroelectric transition at about $250\mathrm{K}$ have been investigated by TEM and off-axis electron holography. Cross-sectional TEM observations show that the $350\text{−}\mathrm{nm}$-thick ${\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Ti}{\mathrm{O}}_3$ film has a sharp interface with notable misfit dislocations. Off-axis electron holographic measurements reveal that, at low temperatures, the ferroelectric polarization results in a remarkable positive potential on the interface and a negative potential on the film surface, and, at room temperature, certain charges could only accumulate at the interfacial dislocations and other defective areas.

• Received 30 September 2004

DOI:https://doi.org/10.1103/PhysRevB.71.115419