Real-time atomistic observation of structural phase transformations in individual hafnia nanorods.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 28497788.
- Also identified by DOI 10.1038/ncomms15316 and PMC identifier 5437304.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
High-temperature phases of hafnium dioxide have exceptionally high dielectric constants and large bandgaps, but quenching them to room temperature remains a challenge. Scaling the bulk form to nanocrystals, while successful in stabilizing the tetragonal phase of isomorphous ZrO<sub>2</sub>, has produced nanorods with a twinned version of the room temperature monoclinic phase in HfO<sub>2</sub>. Here we use in situ heating in a scanning transmission electron microscope to observe the transformation of an HfO<sub>2</sub> nanorod from monoclinic to tetragonal, with a transformation temperature suppressed by over 1000°C from bulk. When the nanorod is annealed, we observe with atomic-scale resolution the transformation from twinned-monoclinic to tetragonal, starting at a twin boundary and propagating via coherent transformation dislocation; the nanorod is reduced to hafnium on cooling. Unlike the bulk displacive transition, nanoscale size-confinement enables us to manipulate the transformation mechanism, and we observe discrete nucleation events and sigmoidal nucleation and growth kinetics.