The stability of B6 octahedron in BaB6 under high pressure

Abstract

We have performed in situ synchrotron X-ray diffraction and first-principles calculations to explore the compression behavior of barium hexaboride (BaB₆) under high pressure. No phase transitions in our experiment are observed up to 49.3 GPa at ambient temperature. It is found that the ambient cage structure (Pmm) is still stable with a basic covalent network during the experimental pressure run. The results of our theoretical calculations show that the ambient structure might transform into three dynamically stable structures (Cmmm, Cmcm and I4/mmm) at 78 GPa, 97 GPa and 105 GPa respectively. The energy band calculations indicate that the sample is still a semiconductor with a narrow gap at 50 GPa.