Hydrogen diffusion and stabilization in single-crystal VO2 micro/nanobeams by direct atomic hydrogenation

Area of Science:

• Materials Science
• Solid-State Physics
• Nanotechnology

Background:

• Vanadium dioxide (VO2) exhibits a metal-to-insulator transition near room temperature.
• Understanding hydrogen diffusion in VO2 is crucial for its applications.
• Atomic hydrogen doping is a potential method for tuning VO2 properties.

Purpose of the Study:

• To measure the diffusion of atomic hydrogen in single crystalline VO2 micro/nanobeams.
• To investigate the effect of atomic hydrogenation on the phase transition of VO2.
• To determine the kinetics of hydrogen diffusion in different VO2 phases.

Main Methods:

• Direct exposure of VO2 micro/nanobeams to catalytically generated atomic hydrogen at 373 K.
• Optical characterization to observe hydrogen diffusion fronts.
• Estimation of hydrogen diffusion constants based on diffusion front movement.
• Ab initio calculations for theoretical validation.

Main Results:

• Atomic hydrogenation stabilizes the metallic phase of VO2 down to 2 K.
• Hydrogen atoms preferentially diffuse along the c-axis of rutile VO2 (a-axis of monoclinic VO2) through oxygen channels.
• The diffusion constant of hydrogen along the c-axis of rutile VO2 at 373 K is 6.7 × 10⁻¹⁰ cm²/s, approximately 38 times higher than in TiO2.
• Diffusion in the monoclinic phase is at least 3 orders of magnitude slower than in the rutile phase.

Conclusions:

• Atomic hydrogen diffusion in VO2 is highly anisotropic, strongly favoring the rutile phase.
• The significant difference in diffusion kinetics between rutile and monoclinic phases is attributed to channel distortion.
• These findings suggest the potential for developing switchable membranes for hydrogen transport based on VO2.