Unusual Low-Temperature Phase in VO$_2$ Nanoparticles

TL;DR

This study investigates the crystal, electronic, and magnetic properties of VO$_2$ nanoparticles, revealing an unusual low-temperature phase with structural and electronic modifications, and discusses the role of the Peierls mechanism in the metal-insulator transition.

Contribution

It provides a detailed analysis of the low-temperature phase in VO$_2$ nanoparticles, highlighting structural and electronic changes and proposing the Peierls mechanism's involvement.

Findings

Discovery of an unusual low-temperature phase with elongated V-V pairs

Observation of a narrowed energy gap and paramagnetic contribution

High-temperature rutile structure similar in nanoparticles and microparticles

Abstract

We present a systematic investigation of the crystal and electronic structure and the magnetic properties above and below the metal-insulator transition of ball-milled VO$_2$ nanoparticles and VO$_2$ microparticles. For this research, we performed a Rietveld analysis of synchrotron radiation x-ray diffraction data, O $K$ x-ray absorption spectroscopy, V $L_3$ resonant inelastic x-ray scattering, and magnetic susceptibility measurements. This study reveals an unusual low-temperature phase that involves the formation of an elongated and less-tilted V-V pair, a narrowed energy gap, and an induced paramagnetic contribution from the nanoparticles. We show that the change in the crystal structure is consistent with the change in the electronic states around the Fermi level, which leads us to suggest that the Peierls mechanism contributes to the energy splitting of the $a_{1g}$ state. Furthermore, we find that the high-temperature rutile structure of the nanoparticles is almost identical to that of the microparticles.