Configurable Crack Wall Conduction in a Complex Oxide

Abstract

Mobile defects in solid-state materials play a significant role in memristive switching and energy-efficient neuromorphic computation. Techniques for confining and manipulating point defects may have great promise for low-dimensional memories. Here, we report the spontaneous gathering of oxygen vacancies at strain-relaxed crack walls in SrTiO 3 thin films grown on DyScO 3 substrates as a result of flexoelectricity. We found that electronic conductance at the crack walls was enhanced compared to the crack-free region, by a factor of 10 4 . A switchable asymmetric diode-like feature was also observed, and the mechanism is discussed, based on the electrical migration of oxygen vacancy donors in the background of Sr-deficient acceptors forming n + −n or n−n + junctions. By tracing the temporal relaxations of surface potential and lattice expansion of a formed region, we determine the diffusivity of mobile defects in crack walls to be 1.4 × 10 −16 cm 2 /s, which is consistent with oxygen vacancy kinetics.

Nanoscale Enhancement of the Local Optical Conductivity near Cracks in Metallic SrRuO3 Film

“…The vertical length scale (depth) of the nanocracks varies from 17 to 53 nm (Figure S5), which means that the nanocracks in the investigated films are deeper than the film thickness. Similar penetration of nanocracks into the substrates has been reported in the earlier oxide thin film studies. , …”

“…Similar penetration of nanocracks into the substrates has been reported in the earlier oxide thin film studies. 14,16 This depth variation suggests that most nanocracks, which are originally generated inside the SRO/STO bilayer, penetrate the STO buffer and propagate into the top region of the KTO substrate. This behavior can be understood by considering the thermal expansion coefficients of the constituting materials, namely, SRO (α L = 1.13 × 10 −5 K −1 ), STO (α L = 9.4 × 10 −6 K −1 ), and KTO (α L = 4.027 × 10 −6 K −1 ), at room temperature.…”

“…Similar penetration of nanocracks into the substrates has been reported in the earlier oxide thin film studies. 14 , 16 …”

“…15 Yeo et al reported that the electrical conductivity near the STO crack wall could be enhanced by a factor of 10 4 by the migration of oxygen vacancies. 16 Most of these works can be interpreted in terms of the microscopic charge redistribution in the insulating oxides near the nanocrack regions. On the other hand, there are still few studies on nanocracks in metallic thin films, where the charge redistribution should be screened by the free carriers.…”

“…Recently, there have been several reports on an emergent phenomena from nanocracks in insulating oxide materials. − For examples, Abdollahi et al . theoretically predicted the relationship between the direction of the polar axis and crack propagation in the piezoelectric material .…”