  We analyzed micrometer-scale titanium-niobium-oxide prototype memristors,
which exhibited low write-power (<3 {\mu}W) and energy (<200 fJ/bit/{\mu}m2),
low read-power (~nW), and high endurance (>millions of cycles). To understand
their physico-chemical operating mechanisms, we performed in-operando
synchrotron x-ray transmission nanoscale spectromicroscopy using an
ultra-sensitive time-multiplexed technique. We observed only spatially uniform
material changes during cell operation, in sharp contrast to the frequently
detected formation of a localized conduction channel in transition-metal-oxide
memristors. We also associated the response of assigned spectral features
distinctly to non-volatile storage (resistance change) and writing of
information (application of voltage and Joule heating). These results provide
critical insights into high-performance memristors that will aid in device
design, scaling and predictive circuit-modeling, all of which are essential for
the widespread deployment of successful memristor applications.

Materials Science