Pressure-Induced Changes in the Crystal Structure and Electrical Conductivity of GeV₄S₈

Lacunar spinels, represented by AM₄X₈ compounds (A = Ga or Ge; M = V, Mo, Nb, or Ta; X = S or Se), form a unique group of ternary chalcogenide compounds. Among them, GeV₄S₈ has garnered significant attention due to its distinctive electrical and magnetic properties. While previous research efforts have primarily focused on studying how this material behaves under cooling conditions, pressure is another factor that determines the state and characteristics of solid matter. In this study, we employed a diamond anvil cell in conjunction with high-energy synchrotron X-ray diffraction, Raman spectroscopy, four-point probes, and theoretical computation to thoroughly investigate this material. We found that the structural transformation from cubic to orthorhombic was initiated at 34 GPa and completed at 54 GPa. Through data fitting of volume vs pressure, we determined the bulk moduli to be 105 ± 4 GPa for the cubic phase and 111 ± 12 GPa for the orthorhombic phase. Concurrently, electrical resistance measurements indicated a semiconductor-to-nonmetallic conductor transition at ∼15 GPa. Moreover, we experimentally assessed the band gaps at different pressures to validate the occurrence of the electrical phase transition. We infer that the electrical phase transition correlates with the valence electrons in the V₄ cluster rather than the crystal structure transformation. Furthermore, the computational results, electronic density of states, and band structure verified the experimental observation and facilitated the understanding of the mechanism governing the electrical phase transition in GeV₄S₈.