ABSTRACT
The octahedral symmetry in ionic crystals can play a critical role in atomic nucleation and migration during solid-solid phase transformation. Similarly, octahedron distortion, which is characterized by Goldschmidt tolerance factor, strongly influences the exsolution kinetics in the perovskite lattice framework during high-temperature annealing. However, a fundamental study on manipulating the exsolution process by octahedron distortion is still lacking. In this study, we accelerate Ni metal exsolution on the surface of perovskite stannates by increasing the [BO6] octahedron distortion in the lattices. Decreasing the A-site ionic radius (rBa2+ = 161 pm â rSr2+ = 144 pm â rCa2+ = 134 pm) increased the density of exsolved Ni nanoparticles by up to 640% (i.e., 47 particles µm-2 of Ba(Sn, Ni)O3 â 304 particles µm-2 of Ca(Sn, Ni)O3) after the identical exsolution process. Based on the theoretical calculation and experimental characterization, the decrease in crystal symmetry by octahedral distortion promoted the Ni exsolution owing to the boosted Ni migration by weakening the bond strength and generating domain boundaries. The findings highlight the importance of octahedral distortion to control atomic migration through the perovskite lattice framework and provide a strategy to tailor the density of uniformly populated nanoparticles in nanocomposite oxides for multifunctional material design.
ABSTRACT
Mott threshold switching, which is observed in quantum materials featuring an electrically fired insulator-to-metal transition, calls for delicate control of the percolative dynamics of electrically switchable domains on a nanoscale. Here, we demonstrate that embedded metallic nanoparticles (NP) dramatically promote metastability of switchable metallic domains in single-crystal-like VO2 Mott switches. Using a model system of Pt-NP-VO2 single-crystal-like films, interestingly, the embedded Pt NPs provide 33.3 times longer 'memory' of previous threshold metallic conduction by serving as pre-formed 'stepping-stones' in the switchable VO2 matrix by consecutive electical pulse measurement; persistent memory of previous firing during the application of sub-threshold pulses was achieved on a six orders of magnitude longer timescale than the single-pulse recovery time of the insulating resistance in Pt-NP-VO2 Mott switches. This discovery offers a fundamental strategy to exploit the geometric evolution of switchable domains in electrically fired transition and potential applications for non-Boolean computing using quantum materials.
ABSTRACT
Programmable optoelectronic devices call for the reversible control of the photocarrier recombination process by in-gap states in oxide semiconductors. However, previous approaches to produce oxygen vacancies as a source of in-gap states in oxide semiconductors have hampered the reversible formation of oxygen vacancies and their related phenomena. Here, a new strategy to manipulate the 2D photoconductivity from perovskite stannates is demonstrated by exploiting spatially selective photochemical reaction under ultraviolet illumination at room temperature. Remarkably, the ideal trap-free photocurrent of air-illuminated BaSnO3 (≈200 pA) is reversibly switched into three orders of magnitude higher photocurrent of vacuum-illuminated BaSnO3 (≈335 nA) with persistent photoconductivity depending on ambient oxygen pressure under illumination. Multiple characterizations elucidate that ultraviolet illumination of BaSnO3 under low oxygen pressure induces surface oxygen vacancies as a result of surface photolysis combined with the low oxygen-diffusion coefficient of BaSnO3 ; the concentrated oxygen vacancies are likely to induce a two-step transition of photocurrent response by changing the characteristics of in-gap states from the shallow level to the deep level. These results suggest a novel strategy that uses light-matter interaction in a reversible and spatially confined way to manipulate functionalities related to surface defect states, for the emerging applications using newly discovered oxide semiconductors.
