Strain-Induced Gradient Distribution of Dopants at a Perovskite Interface

Interfaces often trap dopants for segregation and significantly affect the material properties. Because interfacial segregation sometimes is harmful, revealing mechanisms to reduce the extent of interface segregation is important. Here we investigate the Sr segregation behavior in LaTiO_3.5/LaTiO₃/LaTiO_3.5 sandwich heterostructures by transmission electron microscopy and first-principles calculations. This reveals that Sr atoms prefer to segregate in LaTiO₃ by replacing La atoms rather than LaTiO_3.5. The Sr concentration in LaTiO₃ increases with the thickness of the LaTiO₃ layer and exhibits an obvious gradient distribution. First-principles calculations suggest that the electrostatic potential drives Sr atoms from LaTiO_3.5 to LaTiO₃. The low Sr concentration at the interfaces is induced by an interfacial strain. The sandwiched LaTiO₃ layer changes from n-type conduction to insulation and to p-type conduction with an increase in Sr concentration. The finding that the strain concentration sometimes reduces the extent of interface segregation provides a new approach for the design and regulation of material interfaces.