Ferroelastic Domain Organization and Precursor Control of Size in Solution- Grown Hafnium Dioxide Nanorods

摘要

We demonstrate that the degree of branching of the alkyl (R) chain in a Hf(OR)_4 precursor allows for control over the length of HfO_2 nanocrystals grown by homocondensation of the metal alkoxide with a metal halide. An extended nonhydrolytic sol-gel synthesis has been developed that enables the growth of high aspect ratio monoclinic HfO_2 nanorods that grow along the [100] direction. The solution-grown elongated HfO_2 nanorods show remarkable organization of twin domains separated by (100) coherent twin boundaries along the length of the nanowires in a morphology reminiscent of shape memory alloys. The sequence of finely structured twin domains each spanning only a few lattice planes originates from the Martensitic transformation of the nanorods from a tetragonal to a monoclinic structure upon cooling. Such ferroelastic domain organization is uncharacteristic of metal oxides and has not thus far been observed in bulk HfO_2. The morphologies observed here suggest that, upon scaling to nanometer-sized dimensions, HfO_2 might exhibit mechanical properties entirely distinctive from the bulk.