Oxygen vacancy formation in the SrTiO₃ Σ5 [001] twist grain boundary from first‐principles

Abstract

The SrTiO3 normalΣ5 [001] twist grain boundary (GB) is studied using first‐principles density functional theory calculations. Three types of GB structures, SrO/SrO (S/S), SrO/TiO2 (S/T), and TiO2/TiO2 (T/T), are modeled and their relative thermodynamic stabilities are examined. Our calculations show that the S/S and S/T structures can be formed within appropriate synthesis conditions, with the S/S structure thermodynamically favored over the S/T structure within a wide range of chemical potentials, while the T/T structure is unlikely to form. The segregation behavior of oxygen vacancies is also investigated by calculating oxygen vacancy formation energies with respect to the distance from GB plane. In the S/S system, oxygen vacancies tend to segregate to the layer adjacent to the GB layer, while in the S/T system, oxygen vacancies tend to segregate to the GB layer itself. In both S/S and S/T systems, oxygen vacancy formation energy is lower than that in bulk SrTiO3. To clearly show the experimental conditions necessary to promote oxygen vacancy formation in the 2 GB systems, we also generate grain boundary phase diagrams for oxygen vacancy with respect to synthesis temperature and oxygen partial pressure. Our calculations reveal different segregation behaviors and distributions of oxygen vacancies in the S/S and S/T systems, providing a possible avenue for GB engineering.

Thermally stimulated relaxation and behaviors of oxygen vacancies in SrTiO3 single crystals with (100), (110) and (111) orientations

“…Strontium titanate (SrTiO 3 ) is a well-known versatile, low-cost perovskite oxide. It has been widely applied into capacitors, varistors, thermistors and semiconductor photocatalyst owing to its high dielectric and incipient ferroelectric response, good thermal and chemical stability, and photocorrosion resistibility [3][4][5][6]. The primary defects considered in ABO 3 perovskite are singly and doubly ionized acceptor dopants A′, A″ and shallow donors oxygen vacancies V O ·· , rather than electronic carriers [7].…”

“…The oxygen vacancies with relatively low formation energies can also play a critical role in determining the surface and electronic properties of SrTiO 3 . Experimental and theoretical studies have proved that the lowest energy charge state for oxygen vacancies with chemical stability is +2 in the vast majority of conditions [5,14,15]. Based on the assumption that oxygen vacancies in SrTiO 3 carry positive charges, Chiang et al proposed that oxygen vacancies provide the dominant contribution to tilting grain boundaries by the positive core charge in SrTiO 3 [13].…”

Generating Periodic Grain Boundary Structures: Algorithm and Open-Source Python Library

“…5,6 As one common planar defect, grain boundaries can control microstructural evolution and significantly change the mechanical, electronic, and other properties of polycrystalline materials. [7][8][9][10][11] Investigating the influence of grain boundaries on the materials properties has been an important research subject in materials science. [12][13][14] For instance, grain boundaries in solid electrolytes can often have ionic conductivities that are several orders of magnitude lower than that of bulk, thereby limiting the overall ionic conductivity and severely lowering the device performance.…”