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 VO2 nanoparticles and VO2 microparticles. For this research, we performed a Rietveld analysis of synchrotron radiation x-ray diffraction data, O K x-ray absorption spectroscopy, V L3 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 a1g state. Furthermore, we find that the high-temperature rutile structure of the nanoparticles is almost identical to that of the microparticles.
@article{arxiv.1006.1943,
title = {Unusual Low-Temperature Phase in VO$_2$ Nanoparticles},
author = {Y. Ishiwata and S. Suehiro and M. Hagihala and X. G. Zheng and T. Kawae and O. Morimoto and Y. Tezuka},
journal= {arXiv preprint arXiv:1006.1943},
year = {2015}
}