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Abstract The charge density wave material 1T-TaS2exhibits a pulse-induced insulator-to-metal transition, which shows promise for next-generation electronics such as memristive memory and neuromorphic hardware. However, the rational design of TaS2devices is hindered by a poor understanding of the switching mechanism, the pulse-induced phase, and the influence of material defects. Here, we operate a 2-terminal TaS2device within a scanning transmission electron microscope at cryogenic temperature, and directly visualize the changing charge density wave structure with nanoscale spatial resolution and down to 300 μs temporal resolution. We show that the pulse-induced transition is driven by Joule heating, and that the pulse-induced state corresponds to the nearly commensurate and incommensurate charge density wave phases, depending on the applied voltage amplitude. With our in operando cryogenic electron microscopy experiments, we directly correlate the charge density wave structure with the device resistance, and show that dislocations significantly impact device performance. This work resolves fundamental questions of resistive switching in TaS2devices, critical for engineering reliable and scalable TaS2electronics.
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Abstract BaTiO3heated in an excess of SrCl2at 1150 °C converts to SrTiO3through an ion exchange reaction. The SrTiO3synthesized by ion exchange produces hydrogen from pH 7 water at a rate more than twice that of conventional SrTiO3treated identically. The apparent quantum yield for hydrogen production in pure water of the ion exchanged SrTiO3is 11.4% under 380 nm illumination. The catalyst resulting from ion‐exchange differs from conventional SrTiO3by having ≈2% residual Ba, inhomogeneous Cl‐doping at a concentration less than 1%, Kirkendall voids in the centers of particles that result from the unequal rates of Sr and Ba diffusion together with the transport of Ti and O, and nanoscale regions near the surface that have lattice spacings consistent with the Sr‐excess phase Sr2TiO4. The increased photochemical efficiency of this nonequilibrium structure is most likely related to the Sr‐excess, which is known to compensate donor defects that can act as charge traps and recombination centers.