High-Pressure Synthesis of Novel Ternary Transition Metal Chalcogenide Ba2Re6Se11

A novel ternary transition metal chalcogenide Ba2Re6Se11, which crystallizes in the R−3c space group, was synthesized using a high-pressure and high-temperature technique. The lattice is constituted by Re6Se8 cube-octahedral clusters connected by additional apical Se anions via the Re-Se-Re pathway, while the Ba atoms reside in the cavities among the Re6Se8 units. High-pressure synchrotron X-ray diffraction measurements showed that Ba2Re6Se11 maintains a trigonal structure up to a pressure of 60 GPa, with a bulk modulus of 193 GPa. The lattice stability is ascribed to the fully occupied valence bands of the molecular orbital of the Re6Se8 cluster with trivalent Re. This fully occupied orbital configuration also gives rise to the diamagnetic state of Ba2Re6Se11, which was validated through magnetic measurements. The resistivity of Ba2Re6Se11 is as low as several milliohm centimeters, and it follows the thermal activation mechanism at elevated temperatures and the three-dimensional variable-range hopping model at low temperatures, indicating that Ba2Re6Se11 is a semiconductor or insulator in close vicinity to a metal–insulator transition.