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The discovery of analog LixNbO2 memristors revealed a promising new memristive mechanism wherein the diffusion of Li+ rather than O2− ions enables precise control of the resistive states. However, directly correlating lithium concentration with changes to the electronic structure in active layers remains a challenge and is required to truly understand the underlying physics. Chemically delithiated single crystals of LiNbO2 present a model system for correlating lithium variation with spectroscopic signatures from operando soft x-ray spectroscopy studies of device active layers. Using electronic structure modeling of the x-ray spectroscopy of LixNbO2 single crystals, we demonstrate that the intrinsic memristive behavior in LixNbO2 active layers results from field-induced degenerate p-type doping. We show that electrical operation of LixNbO2-based memristors is viable even at marginal Li deficiency and that the analog memristive switching occurs well before the system is fully metallic. This study serves as a benchmark for material synthesis and characterization of future LixNbO2-based memristor devices and suggests that valence change switching is a scalable alternative that circumvents the electroforming typically required for filamentary-based memristors. 

Abstract Straining the vanadium dimers along the rutilec‐axis can be used to tune the metal‐to‐insulator transition (MIT) of VO₂but has thus far been limited to TiO₂substrates. In this work VO₂/MgF₂epitaxial films are grown via molecular beam epitaxy (MBE) to strain engineer the transition temperature (T_MIT). First, growth parameters are optimized by varying the synthesis temperature of the MgF₂(001) substrate (T_S) using a combination of X‐ray diffraction techniques, temperature dependent transport, and soft X‐ray photoelectron spectroscopy. It is determined thatT_Svalues greater than 350 °C induce Mg and F interdiffusion and ultimately the relaxation of the VO₂layer. Using the optimized growth temperature, VO₂/MgF₂(101) and (110) films are then synthesized. The three film orientations display MITs with transition temperatures in the range of 15–60 °C through precise strain engineering.