Watching Ions Hop in Superionic Nanomaterials

March 2013 SSRL Science Summary by Lori Ann White, SLAC Office of Communications

For the first time, ultrafast x-ray scattering and spectroscopic measurements carried out at SSRL, the Advanced Light Source (ALS) and the Advanced Photon Source (APS) captured the atomic-level dynamics of a superionic nanocrystal as it transformed.

Superionic materials are multi-component solids which can simultaneously display characteristics of both a solid and a liquid: Above a critical temperature associated with a structural phase transition, one atomic species in the material exhibits liquid-like ionic conductivities and dynamic disorder within the rigid crystalline structure of the other. Applications such as electrochemical storage materials and resistive switching devices follow from this abrupt change in ionic mobility, but the atomistic pathways associated with this phase transition and the related functional properties that emerge at the nanoscale have been largely unknown and unexplored.

Measurements carried out on copper sulfide (Cu₂S) nanodiscs using x-ray spectroscopy at ALS, temperature-dependent x-ray spectroscopy SSRL Beam Line 13-3, and hard x-ray scattering at SSRL Beam and at the APS characterized the short- and long-range structural changes associated with the phase transition with time resolution extending down to femtosecond time scales. Together, these measurements showed that the intrinsic time for the transformation is governed by the ionic hopping time in these systems, identifying a transition state in which diffusional motion of the ions leads to the formation of the superionic crystallographic phase. They also indicated that the transition can occur on picosecond time-scales, identifying the possibility of nanoscale superionic-based switching devices controllable by light and operating with speeds orders of magnitude faster than previously demonstrated.

Research supported by the Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.

 

Primary Citation

T. A. Miller, J. S. Wittenberg, H. Wen, S. Conner, Y. Cui, A. M. Lindenberg, "The Mechanism of Ultrafast Structural Switching in Superionic Copper (I) Sulphide Nanocrystals", Nature Communications 4,1369 (2013).

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Contact

Aaron Lindenberg, PULSE/SSRL/Stanford University