High pressure crystalline phases of tellurium

Recent investigations of the pressure induced structural evolution in several elements (mostly Chalcogens and Halogens like S, Se, Te, I, and Br) have provided evidence for the onset of a high pressure (HP) incommensurately modulated (IM) lattice arrangement and a connection of the IM phase with an electronic instability. In this context, Te is a prototype system well suited for an experimental and theoretical investigation of the crystalline and electronic structure stability under pressure. A room temperature study of the high pressure phases of crystalline Te was carried out by combining Raman spectroscopy and Density Functional Theory (DFT) based calculations.

Normalized and background subtracted Raman spectra of Te, collected using NaCl and methanol/ethanol are shown in Fig.1.9 at selected pressure values. The Raman spectrum shows remarkable pressure dependence albeit the three-peaks structure is basically preserved over the whole pressure range and the pressure dependence of the experimental phonon spectrum reveals the occurrence of IM phase transitions. The DFT calculations well reproduce the experimental data and show that the metallization transition, occurring at 4 GPa, is driven by an intra- to inter-chain charge transfer, due to charge-bridges between atoms belonging to adjacent chains (Fig.1.10).