Search

Domain boundaries in perovskite oxides often exhibit abundant physical properties and phenomena. Here, epitaxial LaTiO3 thin films on (100) SrTiO3 substrates are prepared by pulsed-laser deposition. X-ray diffraction and transmission electron microscopy investigations reveal that the epitaxial LaTiO3 thin films have good crystallinity but a high density of domain boundaries. Atomic-scale scanning transmission electron microscopy observations reveal that two types of domain boundaries are formed in the LaTiO3 thin films. The type I domain boundaries are formed on the {100} crystal planes, while the type II domain boundaries on the {110} crystal planes. Electron energy-loss spectroscopy analyses suggest that the valence states of Ti ions at the type I domain boundaries are +3, while those at the type II domain boundaries are +4. First-principles calculations reveal that the bandgap decreases at both domain boundaries compared to the bulk. The carrier concentration at the type I domain boundaries is significantly higher than that of the bulk, while the carrier concentration at the type II domain boundaries is lower. These findings suggest that domain boundaries play an important role in tailoring the electrical properties of the LaTiO3 thin films, thereby promoting the potential applications and property modulation of related materials and devices. [ABSTRACT FROM AUTHOR]

Elemental doping at coherent interfaces is very difficult and rarely used to improve the interfacial properties since coherent interfaces have low interfacial energies and lack open space for trapping dopant atoms. Exploring universally applicable strategies for elemental doping at coherent interfaces represents an important progress in interface science and engineering. In this study, Nb atoms are successfully doped at coherent (001) LaAlO 3 /anatase-TiO 2 interfaces, which enhances greatly the efficiency of photocatalytic hydrogen production from water. Transmission electron microscopy investigations reveal that both LaO- terminated and AlO 2 -terminated LaAlO 3 /anatase-TiO 2 interfaces can trap two layers of Nb atoms, which accompanies with the formation of La vacancies between them. First-principles calculations suggest that Nb atoms segregate at the interfaces under the action of potential gradient, which increases significantly the strength of the built-in electric field in TiO 2 , thereby facilitating the separation of photogenerated carriers and improving the photocatalytic performance. The H 2 production of the Nb doped coherent interface is about 4 times that of the pristine coherent interface. Since potential gradient widely exists at various interfaces including the coherent ones, elemental doping by potential gradient should be an universally applicable fabrication method for tuning the properties of interfaces and heterostructures. [Display omitted] [ABSTRACT FROM AUTHOR]

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 /LaTiO 3 /LaTiO 3.5 sandwich heterostructures by transmission electron microscopy and first-principles calculations. This reveals that Sr atoms prefer to segregate in LaTiO 3 by replacing La atoms rather than LaTiO 3.5 . The Sr concentration in LaTiO 3 increases with the thickness of the LaTiO 3 layer and exhibits an obvious gradient distribution. First-principles calculations suggest that the electrostatic potential drives Sr atoms from LaTiO 3.5 to LaTiO 3 . The low Sr concentration at the interfaces is induced by an interfacial strain. The sandwiched LaTiO 3 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.

Nanotwinned materials have recently attracted intense interest since they often exhibit excellent mechanical properties that are far superior to those of the corresponding single crystals. However, how nanotwinned structures affect the physical properties of functional materials remains almost unexplored. In this study, we demonstrate ferrimagnetism in a nanotwinned antiferromagnetic Cr 2 O 3 thin film. The Cr 2 O 3 thin film grown on the SrTiO 3 substrate comprises high-density nanotwins and exhibits an obvious room-temperature ferrimagnetic property, though the bulk Cr 2 O 3 is intrinsically antiferromagnetic. Aberration-corrected transmission electron microscopy investigations reveal that the twin boundaries (TBs) of Cr 2 O 3 are stoichiometric and have two types of atomic structures (i.e., denoted by type I and type II). First-principles calculations suggest that the type I TB exhibits an antiferromagnetic nature without a net magnetic moment, while the type II TB is ferrimagnetic and has a net magnetic moment of 3.0 μ B /f.u. These findings suggest that nanotwins in functional materials can generate physical properties distinct from those of single crystals, thereby providing an efficient strategy for material design and performance control.

Domain walls affect significantly ferroelectric and magnetic properties of magnetoelectric multiferroics. The stereotype is that the ferroelectric polarization will reduce at the domain walls due to the incomplete shielding of depolarization field or the effects of gradient energy. By combining transmission electron microscopy and first-principles calculations, we demonstrate that the ferroelectric polarization of tail-to-tail 180° domain walls in ε-Fe 2 O 3 is regulated by the bound charge density. A huge enhancement (43%) of ferroelectric polarization is observed in the type I domain wall with a low bound charge density, while the ferroelectric polarization is reduced to almost zero at the type II domain wall with a high bound charge density. The magnetic coupling across the type I and type II ferroelectric domain walls are antiferromagnetic and ferromagnetic, respectively. Revealing mechanisms for enhancing ferroelectric polarization and magnetic behaviors at ferroelectric domain walls may promote the fundamental research and potential applications of magnetoelectric multiferroics., (© 2024. The Author(s).)