Pressure-Induced Amorphization in Single-Crystal Ta<sub>2</sub>O<sub>5</sub> Nanowires: A Kinetic Mechanism and Improved
Electrical Conductivity
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Abstract
Pressure-induced
amorphization (PIA) in single-crystal Ta<sub>2</sub>O<sub>5</sub> nanowires
is observed at 19 GPa, and the obtained amorphous Ta<sub>2</sub>O<sub>5</sub> nanowires show significant improvement in electrical conductivity.
The phase transition process is unveiled by monitoring structural
evolution with <i>in situ</i> synchrotron X-ray diffraction,
pair distribution function, Raman spectroscopy, and transmission electron
microscopy. The first principles calculations reveal the phonon modes
softening during compression at particular bonds, and the analysis
on the electron localization function also shows bond strength weakening
at the same positions. On the basis of the experimental and theoretical
results, a kinetic PIA mechanism is proposed and demonstrated systematically
that amorphization is initiated by the disruption of connectivity
between polyhedra (TaO<sub>6</sub> octahedra or TaO<sub>7</sub> bipyramids)
at the particular weak-bonding positions along the <i>a</i> axis in the unit cell. The one-dimensional morphology is well-preserved
for the pressure-induced amorphous Ta<sub>2</sub>O<sub>5</sub>, and
the electrical conductivity is improved by an order of magnitude compared
to traditional amorphous forms. Such pressure-induced amorphous nanomaterials
with unique properties surpassing those in either crystalline or conventional
amorphous phases hold great promise for numerous applications in the
future