Phase segregation on the nanoscale in Na2C60

TL;DR

This study investigates nanoscale phase segregation in Na2C60 using multiple spectroscopic and scattering techniques, revealing distinct insulating and metallic regions that merge upon heating due to sodium ion diffusion.

Contribution

It provides detailed experimental evidence of phase segregation and its temperature-dependent behavior in Na2C60, which was previously not well understood.

Findings

Nanoscale phase segregation of 3-10 nm regions identified

Presence of insulating C60 phase and metallic Na3C60 confirmed

Phase separation disappears above ~460 K due to sodium ion jump diffusion

Abstract

Na2C60 is believed to be an electron-hole counterpart of the Mott-Jahn--Teller insulator A4C60 salts. We present a study of infrared, ESR, NMR spectroscopy, X-ray diffraction, chemical composition and neutron scattering on this compound. Our spectroscopic results at room temperature can be reconciled in a picture of segregated, separate regions of the size 3--10 nm. We observe a significant insulating C60 phase and at least two more phases, one of which we assign to metallic Na3C60. The separation disappears on heating by jump diffusion of the sodium ions, which we followed by neutron scattering. Above ~460 K we see infrared spectroscopic evidence of a Jahn--Teller distorted (C60)2- anion.