Unusual structure and properties of germanium under pressure

Abstract

Structural phase transitions in group 14 element germanium (Ge) under high pressure were investigated through first-principle calculations along with unbiased CALYPSO structure prediction method. We successfully reproduced experimental structures Fd-3m, I41/amd, Imma, P6/mmm, Cmca and P63/mmc were in our study on crystal structures. In addition, we found four new high-pressure metastable phases (Fmmm(I) and Cmcm at 75 GPa, Fmmm(II) and Fmm2 at 130 GPa). It was found in electronic density of states (DOS) and electronic band structure diagrams that all predicted new phases were metallic phases. The results of crystal structures, X-ray diffraction and phonon dispersion curve showed that our predicted phases (Cmcm and Fmmm(II)) could be incommensurate modulation structures. The findings of this study enriched the phases of Ge under high pressures and offered fundamental insight for further investigation of structural phase transitions in other group 14 elements under high pressures.